The Effect of Caffeine Supplementation on Muscular Endurance in Recreationally Active College Age Males

University of Rhode Island University of Rhode Island

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2016

The Effect of Caffeine Supplementation on Muscular Endurance in The Effect of Caffeine Supplementation on Muscular Endurance in

Recreationally Active College Age Males Recreationally Active College Age Males

Mark Gauvin

University of Rhode Island

, mark_gauvin@my.uri.edu

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College Age Males" (2016).

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THE EFFECT OF CAFFEINE SUPPLEMENTATION ON MUSCULAR

ENDURANCE IN RECREATIONALLY ACTIVE COLLEGE AGE MALES

MARK GAUVIN

A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE

REQUIREMENTS FOR THE DEGREE OF

MASTER OF SCIENCE

NUTRITION AND FOOD SCIENCES

UNIVERSITY OF RHODE ISLAND

2016

MASTER OF SCIENCE THESIS

MARK R. GAUVIN

APPROVED:

Thesis Committee:

Major Professor Kathleen Melanson

Ingrid Lofgren

Disa Hatfield

Nasser H. Zawia

DEAN OF THE GRADUATE SCHOOL

UNIVERSITY OF RHODE ISLAND

2016

ABSTRACT

Objective: Caffeine is a drug consumed regularly by approximately 90% of adults

worldwide, primarily due to its ability to reduce fatigue and increase wakefulness. The

benefit of caffeine consumption on athletic performance in large doses (3-9 mg/kg

body weight or BW) is frequently documented in aerobic athletes. The benefits of

caffeine supplementation in resistance training variables, such as muscular endurance,

has shown mixed results, partially due to the inconsistency of testing variables.

Furthermore, while caffeine supplementation shows promising ergogenic effects in

muscular endurance in elite athletes, it is unknown if this effect translates to the

recreational athlete. Therefore, the purpose of this study is to observe the potential

ergogenic effect caffeine supplementation may have in recreational athletes and to

consider how caffeine habituation may influence individuals’ response to a high

dosage of 7 mg/kg BW.

Design: This study used a randomized, double-blind crossover design. Subjects

performed bench press and Smith machine squat repetitions to failure using 60% of

their respective one repetition maximum (1RM), vertical jump, and isometric squat

tests. Subjects consumed either caffeine equivalent to 7 mg/kg BW or placebo 60

minutes prior to testing. Test sessions were separated by 7 days. Number of complete

bench press and Smith machine squat repetitions, vertical jump height, and isometric

power were evaluated. Rating of perceived exertion (RPE) was also recorded and

assessed. A repeated measures analysis of variance (ANOVA) was used to determine

differences between treatments.

Subjects: Subjects were healthy college age males with at least 6 months of prior

strength training experience (n=23, 22.0±2.2 years).

Results: There was no effect of treatment order. There was a significant increase in

bench press repetitions to failure between caffeine (18.9±3.7) and placebo (17.3±3.7,

p=0.002). There was a significant increase in Smith machine squat repetitions to

failure between caffeine (17.2±4.7) and placebo (15.3±4.5, p=0.018). No significant

difference was found in vertical jump or isometric force plate tests between

treatments. RPE was not statistically different between treatments.

Conclusions: This study suggests that acute caffeine supplementation equivalent to 7

mg/kg BW has an ergogenic effect in recreationally trained males in resistance

training exercises. RPE was not statistically different between treatments, indicating

that caffeine supplementation may also reduce perception of exertion relative to the

amount of work performed immediately following a bout of high-intensity resistance

exercise to failure.

ACKNOWLEDGEMENTS

First and foremost, I would like to give my greatest thanks to my major

professor, Dr. Kathleen Melanson. The enthusiasm you demonstrated sports nutrition

is why I found such an interest in your research lab, and I am forever grateful to have

been a part of it for the past four years.

I would also like to recognize my thesis committee members. Thank you to Dr.

Ingrid Lofgren for challenging me more than anyone else in the department, and for

being one of the most influential people in both my undergraduate and graduate

career. Also, thank you to Dr. Disa Hatfield for sharing your expertise and assistance –

without you and the kinesiology department, I surely would not have found the

success I have. Last but not least, thank you to Dr. Matt Delmonico for serving as my

defense chair and providing insightful questions; because of you, I now know why

plants make caffeine.

Thank you to Linda Sebelia and Cathy English for the many opportunities that

have been provided to me over the years. I am fortunate enough to have had the

pleasure to be both a student and a worker for you both, and the experiences I have

gained are incomparable to any other.

To the dietetic interns - Chelsea, Greg, Jacqueline, Laura, and Kelsi – working

and learning alongside all of you has been the greatest experience, and I believe we

have grown together immensely in such a short time. To Mike Macarthur, I hope to

one day be able to help another with statistics the way you have helped me. To Eric

Nelson, our competition as undergraduates is partially the reason why I am here today,

so I thank you. I also extend my thanks to all of the other graduate students, as you

have made this seemingly endless process not only endurable, but enjoyable.

Additionally, I would like to thank my parents, Lenora and Ron, and my

grandfather, Ray, who have supported and encouraged me since day one. I would also

like to thank my brothers, Adam and Jeff, who have helped make me who I am today.

Last but not least, to my girlfriend Michelle, I thank you especially - for being by my

side for the past eight years and believing in me every step of the way.

Finally, I would like to thank both my grandmother, Ruth, and my uncle,

Rusty, to whom I dedicate this to. I wish you were both here to celebrate this moment

with me, and I can only be so lucky that you were such a monumental part of my life.

PREFACE

This thesis was written to comply with the University of Rhode Island Graduate

School Manuscript Thesis Format. This thesis contains one manuscript entitled “The

Effect of Caffeine Supplementation on Muscular Endurance in Recreationally Active

College Age Males”. This manuscript has been written in a form suitable for

publication in The Journal of Strength and Conditioning Research.

vii

TABLE OF CONTENTS

ABSTRACT…………………………………………………………………………..ii

ACKNOWLEDGEMENTS………………………………………………………....iv

PREFACE…………………………………………………………………………….vi

TABLE OF CONTENTS…………………………………………………………...vii

LIST OF TABLES…………………………………………………………………...ix

LIST OF FIGURES………………………………………………………………......x

MANUSCRIPT……………………………………………………………………….1

ABSTRACT…………….…………….…………….…………….……………3

INTRODUCTION…………….…………….…………….………………….. 4

METHODOLOGY…………….…………….…………….………………….. 5

RESULTS………………….…………….…………….…………….……….11

DISCUSSION. …………….…………….…………….…………….……….11

PRACTICAL APPLICATIONS…………….…………….………………….18

REFERENCES…………….…………….…………….…………….………..20

APPENDICES……………………………………………………………………….27

APPENDIX 1: REVIEW OF THE LITERATURE…………….…………….27

APPENDIX 2: CONSENT FORM…………….…………….……………….46

APPENDIX 3: STUDY TIMELINE…………….…………….………….…..50

APPENDIX 4: TEST DAY TIMELINE……………………………………...51

APPENDIX 5: PRE-SCREENING QUESTIONNAIRE…………………….52

APPENDIX 6: PERSONAL HEALTH HISTORY QUESTIONNAIRE……53

APPENDIX 7: CAFFEINE FREQUENCY QUESTIONNAIRE………...….56

viii

APPENDIX 8: BORG CR-10 SCALE…………….…….……………….…..58

APPENDIX 9: ADDITIONAL TABLES AND FIGURES..………..……….59

APPENDIX 10: FLYER…………….…………….…………….……………67

BIBIOLOGRAPHY…………………………………………………………………68

LIST OF TABLES

TABLE PAGE

Table 1: Subject Characteristics………………………………………………………26

Table 2: Correlations Between Exercise Performance with Caffeine Based on Lean

Body Mass and Self-Reported Habitual Consumption……………………………….59

Table 3: Mean±SD of RPE Before and After Bench Press and Smith Machine Squat

Tests with Caffeine and Placebo Treatments…………………………………………60

LIST OF FIGURES

FIGURE PAGE

Figure 1: Number of Bench Press and Squat Repetitions by Treatment...……….......23

Figure 2: Calculated Vertical Jump Height in cm by Treatment……………………..24

Figure 3: Force Generated During Isometric Force Test by Treatment…………...….25

Figure 4: Relationship Between 1RM Squat and 1RM Bench Press…………………61

Figure 5: Proportion of Subjects Receiving Varying Dosages of Caffeine Based on

Lean Body Mass………………………………………………………………………62

Figure 6: Difference in Individual Number of Bench Press Repetitions to Failure in

Subjects Identified as Low Caffeine Consumers……………………………………..63

Figure 7: Difference in Individual Number of Bench Press Repetitions to Failure in

Subjects Identified as High Caffeine Consumers…………………………………….64

Figure 8: Difference in Individual Number of Smith Machine Repetitions to Failure in

Subjects Identified as Low Caffeine Consumers……………….…………………….65

Figure 9: Difference in Individual Number of Smith Machine Repetitions to Failure in

Subjects Identified as High Caffeine Consumers…………………………………….66

MANUSCRIPT INTRODUCTION PAGE

MANUSCRIPT – 1

To be submitted to the Journal of Strength and Conditioning Research

The Effect of Caffeine Supplementation on Muscular Endurance

in Recreationally Active College Age Males

Mark R. Gauvin, Ingrid E. Lofgren, Disa L. Hatfield, Kathleen J. Melanson

Corresponding Author: Kathleen Melanson, PhD, RD, LDN

Department of Nutrition and Food Sciences

Energy Balance Lab

The University of Rhode Island

41 Lower College Rd, 117D Fogarty Hall

Kingston, RI 02881

Phone: 401.874.4477

Email: [email protected]

The Effect of Caffeine Supplementation on Muscular Endurance

in Recreationally Active College Age Males

ABSTRACT

Caffeine is a substance consumed regularly by approximately 90% of adults

worldwide, primarily due to its ability to reduce fatigue and increase wakefulness. The

benefit of caffeine consumption on athletic performance in moderate doses (3-9 mg/kg

body weight or BW) is frequently documented in cardio-respiratory endurance

athletes. The benefits of caffeine supplementation in resistance training variables, such

as muscular endurance, have shown mixed results, partially due to the inconsistency of

testing variables. Whether recreational athletes experience ergogenic results in

resistance activity from caffeine supplementation is currently unknown. This study

evaluated caffeine’s potential effects at 7 mg/kg BW on resistance training variables in

recreational athletes.

Male subjects (n=23, 22.1±2.2 years) were recruited for this randomized, double-blind

crossover trial. Subjects performed bench press and Smith machine squat repetitions to

failure using 60% 1RM, vertical jump, and isometric squat tests. Subjects consumed

either caffeine equivalent to 7 mg/kg BW or placebo 60 minutes prior to testing.

Number of complete bench press and Smith machine squat repetitions, vertical jump

height, isometric power, and rating of perceived exertion (RPE) were assessed.

Repeated measures ANOVA was used to determine differences between treatments.

Significance was set at p≤0.05. There was no effect of treatment order. There was a

significant increase in bench press repetitions (p=0.002) and Smith machine squat

(p=0.018). This study suggests that acute caffeine supplementation equivalent to 7

mg/kg BW has an ergogenic effect in recreationally trained males in these two

resistance training exercises.

Key words: resistance exercise, repetitions to failure, ergogenic aid

INTRODUCTION

Caffeine, a drug sought for its ability to increase wakefulness and reduce

fatigue, is one of the most widely consumed drugs in the world (29). Caffeine is found

in products such as coffee and tea, soda and energy drinks, ice cream, chocolate, and

nutrition supplements. Evidence suggests caffeine consumption may have an

ergogenic effect in a wide variety of athletic performance, including cardiorespiratory

endurance events and high-intensity, short-duration activities (2, 13, 14, 22, 27). While

the effects of caffeine on aerobic performance have been investigated extensively in

exercises such as running, cycling, and rowing, the effect of caffeine in resistance

training variables such as muscular endurance are inconclusive (5, 13).

A common method of measuring muscular endurance in caffeine trials is by

having subjects perform repetitions to failure using a percentage of their maximum

lifting ability, or 1-repetition maximum (1RM) (10). A study by Woolf, et al. (34)

found no significance between treatments in bench press to fatigue in caffeine-naïve

collegiate football athletes using 5 mg/kg, while Duncan, et al. (11) found significance

in bench press repetitions to failure using the same dosage in University-level rugby,

football, and basketball players. A study by Astorino, et al. (2) found no differences

between treatments in resistance-trained men who ingested caffeine equivalent to 6

mg/kg. While a limited amount of literature exists evaluating lower doses of caffeine,

the consensus suggests there is not an ergogenic effect in muscular endurance at 5-6

mg/kg body weight (BW) (2, 10).

The majority of existing research focuses on subjects of elite athletic status,

often with several years of experience in resistance training exercise. Less research has

been performed on the impact of acute caffeine ingestion on strength and endurance in

the average individual who participates in light to moderate consistent physical

activity. Therefore, in our study, we had recreationally trained athletes perform a

combination of resistance exercises incorporating large muscle groups in both upper

and lower body while ingesting a dose of caffeine equivalent to 7 mg/kg of body

weight. Our primary hypothesis is that acute caffeine ingestion in the amount of 7

mg/kg of body weight will increase the number of bench press repetitions to failure

compared to placebo ingestion in college age, recreational male athletes. Our

secondary hypotheses is that acute ingestion of caffeine will also increase the number

of squat repetitions to failure, increase the amount of force generated from a vertical

jump and isometric squat exercise, and decrease rating of perceived exertion (RPE) at

the time of testing, when compared to placebo ingestion.

Furthermore, previous studies have not taken body composition into

consideration for caffeine dosing (2, 13, 22). Considering caffeine metabolism does

not occur in adipose tissue (1), our exploratory hypothesis is that subjects with lower

body fat percentage will demonstrate a significant increase in repetitions to failure in

bench press and squat exercises when ingesting caffeine when compared to subjects

with a higher body fat percentage.

METHODS

Experimental Approach to the Problem

This study employed a within-subjects, repeated-measures design. Through

informed consent, subjects were notified they were participating in a research study

examining the effect of caffeine as an ergogenic aid on resistance exercise

performance. Subjects were made aware they would be asked to perform a 1RM test

on the bench press and Smith machine squat, and on two subsequent testing sessions

they would be required to perform bench press and Smith machine squat exercises to

failure at an intensity of 60% 1RM following ingestion of capsules containing either

caffeine equivalent to 7 mg/kg BW or a placebo. Subjects were told they would not be

informed which order they would receive each treatment, and that the researchers

performing the study were also unaware. Since prior research has demonstrated that

acute caffeine ingestion may impact a range of physiological and performance

variables, the experimental design (caffeine vs. placebo ingestion) was used to

examine the effect of the independent variable on the following dependent variables

that previous authors have suggested are influenced by caffeine ingestion: bench press

repetitions to failure, Smith machine squat repetitions to failure, vertical jump height,

isometric force, and RPE. All testing took place within the institution’s health fitness

laboratory.

Subjects

After approval from the university’s Institutional Review Board and collection

of subjects’ individually signed informed consents, 24 males (22.1±2.2 years)

completed the testing protocol. As inclusion criteria, all subjects were free from any

musculoskeletal pain or disorders, and reported a minimum of 6 months of consistent

resistance training for at least two days a week. Subjects with a weight greater than

225 lbs. (102 kg) were not enrolled in the study in order to prevent dosages exceeding

double the daily amount generally recognized as safe (400 mg) (19). Additional

exclusion criteria included smoking, medical history significant for hypertension,

diabetes, renal insufficiency, cardiac abnormality, or other chronic disease. Subjects

were asked to refrain from vigorous exercise 48 hours before testing. In addition,

subjects were provided a list of caffeine-containing products and were asked to abstain

from caffeine-containing products beginning at 6:00pm the evening before each

testing session. This was verified via a modified caffeine consumption questionnaire

completed for the 24-hour period before each session, as well as a 24-hour food recall.

Of the 24 subjects recruited, 1 subject was removed for not adhering to the pre-testing

protocol.

Procedures

Subjects attended the Health Fitness Laboratory (HFL) during each visit, all on

an individual basis. The first visit also included collection of anthropometric data in

the Body Composition Laboratory (BCL), where height, weight, and body fat

percentage were collected. Height in centimeters was measured using a Seca 216

stadiometer (Seca, Hanover, MD) to the nearest tenth of a centimeter. Weight was

measured in kilograms with a Tanita scale (Tanita Corporation, Japan) to the nearest

tenth of a kilogram. Height and weight were measured using standard procedures (24),

and body mass index (BMI) was calculated as kg/m

. Body composition was assessed

by air displacement plethysmography using a Bod Pod and its respective software

(Cosmed, Concord, CA). Standard procedures, including Bod Pod calibration prior to

data collection, were followed (31). Total body estimates of percent fat were

computed from the measured body volume using the Siri equation (28). During the

initial visit, 1RM strength testing for the bench press and squat exercises was

conducted using National Strength and Conditioning Association (NSCA) guidelines

in the HFL (3). In addition, subjects completed a health history questionnaire and

caffeine frequency questionnaire for screening and descriptive purposes, during the

initial visit.

Muscular Strength

During the pre-test visit, subjects were asked to estimate their 1RM for the

bench press and Smith machine squat. For each exercise, fifty percent of their stated

1RM was calculated, and subjects were asked to perform 5-10 complete repetitions.

After 3 minutes of rest, subjects were asked to perform 3-5 complete repetitions based

on 70% of their stated 1RM. Subjects then would perform 1-2 repetitions of gradually

increasing weights, with three minute rests in between, until they were no longer able

to complete a full repetition. This was performed to estimate the maximum amount of

weight the subject can lift one time and served as the value for calculating the amount

of weight to be used during testing visits (9).

Muscular Force and Calculated Vertical Jump Height

Muscular power was assessed by an isometric squat and vertical jump exercise.

Force and power were measured using a force plate and Accupower software (AMTI,

Watertown, MA). Following subject familiarization of the isometric squat protocol,

subjects were asked to stand on the force plate in a quarter-squat position under a

Smith machine squat bar. Once in position, subjects were asked to push against the

stationary bar maximally for 10 seconds. Knee angle was measured with a goniometer.

Angle of the knee can be within a range of 100-135 degrees; this number was the same

for both test trials (18).

Subjects were also familiarized with the vertical jump protocol and asked to

perform three consecutive, maximal effort jumps. Procedure for the vertical jump

required subjects to have hands placed on their hips and feet shoulder-length apart

during the exercise. Subjects performed this exercises an additional two times, with 2-

3 minutes of rest between each set. The highest force, power, and jump height in the

three sets were recorded and averaged.

Muscular Endurance

Muscular endurance for both the bench press and Smith machine squat were

assessed using 60% of the subjects’ measured 1RM. Following familiarization of the

exercise protocol, subjects were asked to perform a single set of repetitions of each

exercise until failure. A trained tester was used to count the number of repetitions

completed and to ensure each repetition was completed with proper form. A second

trained tester was present to assist with counting complete repetitions performed.

Rating of Perceived Exertion

RPE was assessed before and after each exercise using the Borg CR-10 scale

(8). Prior to the start of exercises, instructions on how to use the Borg CR-10 scale

were read to each subject. The scale is ranked from 0 (resting state) to 10 (maximal

effort) and assesses how strenuously the subject perceived he worked, based on the

self-reported number chosen.

Caffeine and Placebo Administration

Subjects were supplied caffeine in the form of encapsulated powder. Seven

mg/kg BW were used to determine the total dose for each subject. Placebo capsules

were filled with microcrystalline cellulose free of the eight major allergens as well as

gluten. Caffeine or placebo was ingested one hour prior to experimental trials to

achieve maximum plasma concentration (16). Subjects were provided 12 fluid ounces

of water to aid in capsule ingestion. Once the subject had ingested caffeine or placebo

capsules, he remained stationary for 45 minutes, viewing TED Talks© or reading

magazines. At 45 minutes, subjects were tested for hydration status by using a

refractometer. Inadequate hydration was determined by a specific gravity of 1.024 or

greater (25). Subjects who were found to be inadequately hydrated were provided an

additional 12 fluid ounces of water to consume.

Statistical Analysis

G-power (G*Power, Version 3.1.9.2) was used to determine sample size using

results from a similar study analyzing bench press repetitions in collegiate athletes

ingesting 5 mg/kg body weight of caffeine versus placebo (12). An alpha level of 0.05,

with an effect size = 1 and power = 0.8; this revealed an adequate sample size of 23

subjects. Data were analyzed using SPSS (version 23; SPSS, Inc. Chicago, IL). A

repeated measures analysis of variance (ANOVA) was used to analyze the primary

and secondary hypotheses. Assumptions for normality were tested and met for all

variables using skewness and kurtosis. Pearson correlations were run to examine

exploratory hypotheses. For RPE, a 2x2 repeated measures ANOVA was run to

compare pre and post RPE values with both the caffeine and placebo treatment.

Significance for all analyses were set at p≤0.05.

RESULTS

Subject demographics are presented in Table 1. Mean BMI was 25.5±3.0

kg/m

. Body fat percentage was 15.8±16.4. Mean 1RM was 92.2±22.8 kg in the bench

press and 114.7±22.9 kg in the squat test.

Results indicated that subjects completed significantly more repetitions to

failure with the caffeine treatment compared to placebo in both the bench press (mean

difference of 1.4 repetitions, p=0.006) and Smith machine squat (mean difference of

1.5 repetitions, p=0.032) (Figure 1). Treatment order was not significant in either test.

There were no significant differences in average vertical jump height (Figure 2) or

isometric force (Figure 3) between treatments.

With respect to lean body mass, no correlations were found with performance

in the caffeinated condition in the bench press or Smith machine squat tests. No

correlations were found in bench press or Smith machine squat tests with self-reported

caffeine habituation under the caffeinated condition. Data not shown.

Rating of perceived exertion was not significantly influenced by condition

bench press or squat tests, as determined by 2 (time) x 2 (treatment) repeated measures

ANOVA. Rating of perceived exertion was significant in the isometric squat test

between treatment and time; however, significance was lost when controlling for

treatment order.

DISCUSSION

Both the bench press and Smith machine squat tests resulted in a significant

increase in number of repetitions when subjects received the caffeine treatment

compared to placebo (Figure 1). These results are consistent with previous studies

performed in individuals with a greater training status (2, 11). Astorino et al. (2)

observed 19.9±4.3 repetitions in the caffeine condition versus 18.4±4.0 with placebo

in a study evaluating 22 resistance-trained males with a training history of 6.0±2.8

years. This mean difference of 1.5 repetitions in the bench press is nearly identical to

that observed in the present study (1.4 repetitions) (2). Duncan et al. (11) observed an

average of 22.4±3.0 repetitions in the caffeine condition and 20.4±3.4 with placebo,

resulting in an increase of 2 repetitions - 0.6 repetitions greater than observed in the

present study. In that study, all subjects were highly experienced in the respective

sport (rugby, basketball, football) at the University level and have been competing in

their sport for a mean time of 10.4±2.3 years (11). Therefore, the present study

suggests that caffeine supplementation in recreational athletes has similar ergogenic

effects to that which has been observed in athletes trained in their respective sports for

longer durations.

This study examined the acute effect of a high dose of caffeine on muscular

endurance and sought to address gaps in the literature by employing a design where

multiple resistance exercises were utilized and a population of recreationally trained

athletes was analyzed. Employing the bench press, Smith machine squat, and

isometric force plate arguably create a greater level of fatigue than studies examining

performance in a single exercise. The bench press test in particular is an exercise

frequently used in studies evaluating the impact of caffeine in muscular endurance;

employing this test in our study allows us to compare efficacy in our population with

groups that have been previously evaluated (2, 5, 32). The present study also sought to

recruit subjects who participate in resistance training activity on a recreational basis,

which was defined as a minimum of twice a week for a period of at least six months.

Other researchers have suggested that caffeine may have different effects for

upper- versus lower-body exercise (5, 10). Davis et al reported that the ergogenic

effect of caffeine may not elicit effects for leg musculature until later into an exercise,

when fatigue plays a more prominent role, compared to earlier sets of repetitions (10).

In contrast, tests using upper-body musculature have shown greater improvements in

earlier sets, such as a study by Beck et al which found significant increases in bench

press repetitions to failure, but not in bilateral leg extension (5).

The increases in both upper and lower endurance exercises observed in the

present study are not consistent with previous literature, and may be explained due to

the population recruited. Previous literature has questioned whether the ergogenic

properties of caffeine are limited by the amount of muscle mass recruited and the total

number of repetitions performed (10). This question is plausible given the absorptive

properties of caffeine: when absorbed, caffeine is able to distribute freely into

intracellular tissue water, allowing the transport to metabolic tissue such as the muscle

and brain (1). Therefore, our exploratory hypothesis sought to determine whether

subjects with a lower body fat percentage (and thus a higher percentage of

metabolically active tissue) would benefit from the ergogenic effects of caffeine than

those with a higher body fat percentage. To the researchers’ knowledge, this is the first

study examining the dosage each subject received based on lean body mass. The range

of body fat percentages recorded was 5.8-27.1%, and the caffeine dosage averaged 8-9

mg per kg lean tissue. Despite this, there were no significant correlations between

calculated body fat percentage and performance in any of the four tests when subjects

received the caffeine treatment. This suggests that the ergogenic effect of caffeine was

not greater in individuals with a lower body fat percentage.

Additionally, there was no correlation in performance in the bench press or

Smith machine squat tests with caffeine habituation. An early review article by

Graham concluded that any differences caused by caffeine habituation do not appear

to be significant (16). Moreover, a study by Astorino et al. evaluated the efficacy of 6

mg/kg BW caffeine versus placebo on bench press, leg press, lat row, and shoulder

press; results found that 66% of subjects who demonstrated increases in the caffeine

condition were relatively heavy caffeine users, while subjects who had reduced

performance in the caffeine condition consumed less than 150 mg/day (2). Of note, the

study had a sample size of 14 men with resistance training experiences >2 days/week

for 7.5+1.2 years, who all identified as daily caffeine consumers; as a result, it cannot

be concluded that caffeine habituation has a significant impact on resistance training

variables (2).

Bloms et al. reported significantly higher vertical jump performance in

Division I collegiate athletes who consumed 5 mg/kg BW of caffeine (7). They

concluded the ergogenic of caffeine in vertical jump performance is likely to only be

observed in subjects who are frequently exposed to repeated ballistic tasks, such as

basketball and volleyball players (7). The current study did not recruit individuals

based on experience in sports or other activities that may predispose individuals to

activities requiring frequent jumping (Figure 2). Furthermore, subjects were not

familiarized with the vertical jump protocol prior to the test visits. To our knowledge,

there has not been a caffeine trial in vertical jump exercises in recreationally active

athletes naïve to ballistic activity. Therefore, is it plausible that the proposed

conclusion by Bloms et al. may explain the results witnessed in the present study,

which found no significant difference in calculated vertical jump height (7).

Previous literature has hypothesized that caffeine does not alter maximal force-

generating capacity of a muscle, but may extend time to fatigue by altering pain

perception (10). This would explain the results observed from the isometric force test,

which had no significance between the caffeine treatment and placebo (Figure 3). To

the researchers’ knowledge, this may be the first study to use the isometric force test

in order to measure maximal isometric force generation in recreational athletes.

Results from the present study support the hypothesis that caffeine does not

significantly alter maximal force-generating capacity.

While there are several mechanisms that may play a role in the observed

ergogenic effects of caffeine, the most prominent mechanism of action involves

caffeine’s ability to inhibit adenosine receptors (20). Adenosine, a molecule similar in

structure to caffeine has been shown to enhance pain perception, induce sleep, and

reduce arousal, among other functions (6, 23, 30). Caffeine, which has a nonselective

affinity to adenosine receptors, can bind to adenosine receptors in the brain and

peripheral tissues (15). The resulting inability of adenosine to bind to receptor sites

prevents the adenosine-induced suppression of dopamine release (10). This contributes

to the reported increase in arousal and alertness frequently associated with caffeine

intake (26). As a result, it is believed that the primary mechanism of action is

inhibitory effects on adenosine modifying pain perception while sustaining motor unit

firing rates, resulting in an overall ergogenic effect (10). The resulting inhibition of

adenosine in the presence of caffeine may justify why a significant improvement was

found in the two tests that utilized muscular endurance, but not in the tests that

evaluated a short-duration (<10 second) bout of force, such as the isometric force test,

or the vertical jump test, which arguably did not drastically increase subjects’

perceived exertion (7, 10).

Rating of perceived exertion was not significantly different in the bench press

or Smith machine squat test between treatments. These results are consistent with a

range of studies that have also found no difference in RPE with resistance exercise (4,

11, 17, 33). A proposed reason for the lack of a dampening effect on RPE following

caffeine ingestion is the short duration in exercise to failure in a given exercise (such

as bench press or squats) is insufficient to elicit a perceived difference in exertion

between treatments (11). Evaluating caffeine supplementation at later time points

following resistance training exercise has shown decreased perception of exertion in

caffeine treatments. For example, Hurley et al (21) found decreased perception of

exertion following bench press exercises at 72 hours post-exercise.

Despite the non-significant findings in this current study, subjects had

improved performance in the bench press and squat tests without having a significant

change in RPE between treatments. This is in opposition of the results of a study by

Duncan et al, where subjects had no significant difference in number of bench press

repetitions between 5 mg/kg caffeine and placebo, but did have a lower RPE in the

caffeine condition (13). As a result, it can be argued that RPE was not reduced as a

result of the caffeine treatment in the present study, but perception of exertion was

maintained in the caffeine treatment while subjects completed an additional 1.4

repetitions, on average.

There were several limitations to this study. This study sought out to evaluate a

population of recreationally trained athletes. While all subjects recruited met the

minimum requirements, there was large variability in training experience among

subjects, ranging from the minimum requirements to amateur power lifter. Number of

years of resistance training experience was not documented. Subjects were primarily

Caucasion; future research should recruit a more diverse population to increase

generalizability. Additionally, some subjects noted discomfort when using the Smith

machine – particularly when performing the ISO test, which required subjects to exert

themselves onto a bar anchored in place. For this reason, subjects may have

unconsciously chose to exert themselves less on the second visit compared to the first.

However, to control for potential order effects, the order that subjects received each

treatment was randomized; no significant differences were found in perceived exertion

between the first and second visit. Also, there were two investigators who conducted

the subjects’ test sessions. However, both testers were trained by the same researcher.

Furthermore, analysis determined there was no significant difference in any of the four

tests when controlled for investigator.

In contrast to the limitations, there were many strengths to the study. First, the

study was a double-blind, cross-over design. Also, each subject acted as his own

control. This randomization of treatment order limits the chance of improvement due

to test familiarization. Finally, several steps were taken to ensure that all measures

were taken in an identical manner. Hydration status was tested to ensure subjects were

adequately hydrated prior to testing by determining urine specific gravity. Subjects

met at the same time of day for each visit. Subjects abstained from physical activity

for 48 hours prior to test days and caffeine-containing products from 6:00pm the

evening before testing. Additionally, subjects were instructed to consume the same

meal on each test day; this was confirmed by performing a 24-hour food recall prior to

testing. Finally, this study evaluated recreational athletes, a population that makes up a

greater percentage of the population when compared to elite athletes. For this reason,

the results of this study are applicable to a larger population.

PRACTICAL APPLICATIONS

The effectiveness of caffeine supplementation to improve performance in

resistance training exercise in recreational athletes remains somewhat unclear. The

results of this investigation demonstrate that caffeine increases number of repetitions

in muscular endurance exercises that employ large upper and lower muscle groups

such as the bench press and Smith machine squat. Caffeine habituation status does not

appear to have an impact on the potential ergogenic effects of caffeine. While the

average increase in repetitions was considerably low (1.4 repetitions in the bench press

and 1.5 repetitions in squats), the increases in repetitions over time may be favorable

in the population observed, due to a chronic training effect. While one set of

repetitions to failure was employed for this test, future research should evaluate the

same population using multiple sets of repetitions, as caffeine supplementation may

increase muscular endurance while maintaining RPE as demonstrated in the present

study. However, despite the observed increases in muscular endurance measures, a

high dose of caffeine was required to achieve the observed results. The practical use of

such a dosage (7 mg/kg BW) in a free-living environment is questionable. As with any

supplement study, there will be subjects who respond to treatment and those who not

only do not respond, but also experience an undesirable effect. For this reason, health

professionals and educators should consider recommending caffeine trials to clients on

an individual basis to determine if supplementation will yield desired results.

REFERENCES

1. Arnaud MJ. The pharmacology of caffeine. Prog Drug Res 31: 273-313, 1987.

2. Astorino TA, Rohmann RL, Firth K. Effect of caffeine ingestion on one-

repetition maximum muscular strength. Eur J Appl Physiol 102: 127-132,

2008.

3. Baechle T, Earle R. Essentials of Strength Training and Conditioning.

Champaign, IL, 2008.

4. Beck TW, Housh TJ, Malek MH, Mielke M, Hendrix R,. Acute effects of a

caffeine containing supplement on bench press strength and time to exhaustion.

J Strength Cond Res 22: 1654-1658, 2008.

5. Beck TW, Housh TJ, Schmidt RJ, Johnson GO, Housh DJ, Coburn JW, Malek

MH. The acute effects of a caffeine-containing supplement on strength,

muscular endurance, and anaerobic capabilities. J Strength Cond Res 20: 506-

510, 2006.

6. Bjorness TE, Greene RW. Adenosine and sleep. Current Neuropharmacology

7: 238-245, 2009.

7. Bloms LP, Fitzgerald JS, Short MW, Whitehead JR. The effects of caffeine on

vertical jump height and execution in collegiate athletes. J Strength Cond Res,

2015.

8. Borg GA. Human Kinetics: Borg's perceived exertion and pain scales.

Champaign, IL, 1998.

9. Brown LE, Weir JP. ASEP procedures recommendation i: accurate assessment

of muscular strength and power. J Exercise Physiology 4: 1-21, 2001.

10. Davis JK, Green JM. Caffeine and anaerobic performance: ergogenic value

and mechanisms of action. Sports Med 39: 813-832, 2009.

11. Duncan MJ, Oxford SW. The effect of caffeine ingestion on mood state and

bench press performance to failure. J Strength Cond Res 25: 178-185, 2011.

12. Duncan MJ, Oxford SW. Acute caffeine ingestion enhances performance and

dampens muscle pain following resistance exercise to failure. J Sports Med

Phys Fitness 52: 280-285, 2012.

13. Duncan MJ, Stanley M, Parkhouse N, Cook K, Smith M. Acute caffeine

ingestion enhances strength performance and reduces perceived exertion and

muscle pain perception during resistance exercise. Eur J Sport Sci 13: 392-399,

2013.

14. Dunford M, Doyle JA. Nutrition for Sport and Exercise. Belmont, CA: Peter

Adams, 2008.

15. Fredholm BB, Battig K, Holmen J, Nehlig A, Zvartau EE. Actions of caffeine

in the brain with special reference to factors that contribute to its widespread

use. Pharmacol Rev 51: 83-133, 1999.

16. Graham TE. Caffeine and exercise: metabolism, endurance and performance.

Sports Med 31: 785-806, 2001.

17. Green J, Wickwire P, McLester J, Gendle S, Hudson G, Pritchett R, Laurent C.

Effects of caffeine on repetitions to failure and ratings of perceived exertion

during resistance training. Int J Sports Phys Perf 2: 250-259, 2007.

18. Harris GR, Stone MH, Obryant HS, Proulx CM, Johnson RL. Short-term

performance effects of high power, high force, or combined weight-training

methods. J Strength Cond Res 14, 2000.

19. Heckman MA, Weil J, Gonzalez de Mejia E. Caffeine (1,3,7-

trimethylxanthine) in foods: a comprehensive review on consumption,

functionality, safety, and regulatory matters. J Food Sci 75(3): R77-87, 2010.

20. Holtzman SG, Mante S, Minneman KP. Role of adenosine receptors in

caffeine tolerance. J Pharmacol Exp Ther 256: 62-68, 1991.

21. Hurley CF, Hatfield DL, Riebe DA. The effect of caffeine ingestion on delayed

onset muscle soreness. J Strength Cond Res 27: 3101-3109, 2013.

22. Jacobson BH, Weber MD, Claypool L, Hunt LE. Effect of caffeine on

maximal strength and power in elite male athletes. Br J Sp Med 26: 276-280,

1992.

23. Kalmar JM. The influence of caffeine on voluntary muscle activation. Med Sci

Sports Exerc 37: 2113-2119, 2005.

24. Lohman TG, Roche AF, Martorell R. Anthropometric standardization

reference manual. Champaign, IL: Human Kinetics Books, 1988.

25. Minton DM, ONeal EK, Torres-McGehee TM. Agreement of urine specific

gravity measurements between manual and digital refractometers. J Athletic

Training 50: 59-64, 2015.

26. Nehlig A. Is caffeine a cognitive enhancer? J Alzheimers Dis 20: 85-94, 2010.

27. Norager CB, Jensen MB, Madsen MR, Laurberg S. Caffeine improves

endrance in 75-yr-old citizens: a randomized, double-blind, placebo-controlled

crossover study. J Appl Physiol 99: 2302-2306, 2005.

28. Siri WE. Body composition from fluid space and density. Washington, DC:

National Academy of Science, 1961.

29. Spriet LL. Caffeine and performance. Int J Sports Nutrition 5: S84-99, 1995.

30. Sylvén C, Jonzon B, Fredholm BB, Kaijser L. Adenosine injection into the

brachial artery produces ischaemia like pain or discomfort in the forearm.

Cardiovasc Res 22: 674-678, 1988.

31. Wagner DR, Heyward VH, Gibson AL. Validation of air displacement

plethysmography for assessing body composition. Med Sci Sports Exerc 32:

1339-1344, 2000.

32. Williams AD, Cribb PJ, Cooke MB, Hayes A. The effect of ephedra and

caffeine on maximal strength and power in resistance-trained athletes. J

Strength Cond Res 22: 464-470, 2008.

33. Woolf K, Bidwell WK, Carlson AG. The effect of caffeine as an ergogenic aid

in anaerobic exercise. Int J Sports Nut Exerc Metab 18: 412-429, 2008.

34. Woolf K, Bidwell WK, Carlson AG. Effect of caffeine as an ergogenic aid

during anaerobic exercise performance in caffeine naïve collegiate football

players. J Strength Cond Res 25: 1363-1369, 2009.

ACKNOWLEDGEMENTS

This work was funded by the Undergraduate Research Initiative Grant and the

Continuing Research Grant at the University of Rhode Island. Results of this study do

not constitute endorsement of the product by the authors or the NSCA.

FIGURES

Figure 1: Number of Bench Press and Squat Repetitions by Treatment

BP=Bench press, S=Squat. (n=23) Data analyzed using repeated measures ANOVA. There was a

significant increase in repetitions to failure between caffeine and placebo treatments in both the bench

press and squat tests. *p<0.05, **p<0.01.

BP'Caffeine BP'P lacebo S'Caffeine S'Placebo

Number' of'repetitions' to' failure

**!

Figure 2: Calculated Vertical Jump Height in cm by Treatment

(n=23) Average calculated vertical jump height in cm by treatment. Subjects performed three sets of

three jumps, with the highest average jump height recorded. Data analyzed using repeated measures

ANOVA. No significance found between caffeine and placebo treatment.

Caff eine Placebo

Average:height:in:cm

Figure 3: Force Generated During Isometric Force Test by Treatment

(n=23) Force generated in isometric force plate test by treatment. Data analyzed using repeated

measures ANOVA. No difference between caffeine and placebo treatment.

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TABLES

Table 1. Subject Characteristics

Characteristics of subjects (n=23). 1RM Squat = 1 repetition maximum in squat

exercise, 1RM Bench Press = 1 repetition maximum in bench press exercise.

Anthropometrics are presented as mean ± SD.

Gender

Male

23 (100%)

Ethnicity

African-American

2 (8.7%)

Asian-American

1 (4.3%)

Caucasian

18 (78.3%)

Hispanic/Latino

2 (8.7%)

Height (cm)

176.4 ± 6.4

Weight (kg)

79.5 ± 9.9

BMI (kg/m

)

25.5 ± 3.1

Body fat (%)

15.8 ± 6.6

Age (years)

22.1 ± 2.2

1RM Squat (kg)

115.8 ± 22.7

1RM Bench press (kg)

93.1 ± 22.8

Self-Reported Caffeine Intake

Abstain

4 (17.4%)

Low

11 (47.8%)

Moderate

4 (17.4%)

High

4 (17.4%)

Self-reported caffeine intake is defined as: abstain: ≤ 8 oz. caffeine-containing products per week; low:

≤ 8 oz. caffeine-containing products per day; moderate: 8-16 oz. caffeine-containing product per day;

high: >16 oz. per day.

Appendix I: Review of the Literature

Overview

This literature review will discuss different types of resistance training

variables – specifically, muscular strength and muscular endurance – and provide a

synopsis of the previous literature on cardio-respiratory endurance and resistance

training trials utilizing caffeine as an ergogenic aid. First, we will define strength and

endurance and provide methods of measuring muscular strength, muscular endurance,

and vertical jump height. Then, we will discuss the availability of caffeine in the diet

along with its absorption, metabolism, and several potential mechanisms that may

explain its ergogenic effects in athletic exercises. Finally, we will provide an overview

of the previous literature describing caffeine as an ergogenic aid in both cardio-

respiratory endurance and resistance training.

Resistance Training Variables

Muscular Strength

Muscular strength is defined as the maximum force or torque produced by a

muscle group in an isometric action at a specific joint angle (42). The 1-repetition

maximum (1RM) is currently the gold standard for determining isotonic strength (15).

The American Society of Exercise Physiologists recommend performing 1RM squat

and 1RM bench press tests to assess lower body and upper body strength, respectively

(15). However, 1RM testing is perceived as a potentially dangerous test to perform;

for that reason, methods that employ using a submaximal weight (<1RM) to estimate

1RM in athletes are often used (15). Repetitions with a submaximal weight (<1RM)

are used to accurately estimate 1RM performance in strength endurance exercises,

such as the bench press (49). Estimated 1RM can be accurately calculated by

employing up to 10 repetitions using submaximal weight, such as in a 5RM or 10RM

test (65).

Previous studies have shown that lighter loads, such as 40 and 60% 1RM,

lifted to exhaustion can accurately predict 1RM bench press strength (5, 38). However,

absolute load tests are alternative methods to predicting 1RM by utilizing a constant

weight; these methods have also been found to be accurate predictors of 1RM in

college-age men (38). The most common absolute load test, utilized by the National

Football League as well as at the college and high school level, employs performing

the maximum number of repetitions possible using constant weight of 225 pounds

(50). Results from this test, known as the NFL-225 Test, has been shown to accurately

calculate 1RM; however, the absolute load test is only able to be used in subjects

whose 1RM bench press is greater than 225 pounds (15, 50). In research such as the

present study where subjects recruited have a wide range of strength training

experience, this method of calculating 1RM is not suitable. For this reason, we utilized

each subject’s own submaximal weight as a method to calculate 1RM. This way, the

amount of weight used for each subject was relative to his individual resistance

training ability.

Muscular Endurance

In most laboratory studies, endurance performance is measured as the time

taken to reach exhaustion at a given power output (70). Resistance training programs

that emphasize muscular endurance typically involve many repetitions – typically 12

or more – per set (4). Despite this high number of repetitions, loads lifted are lighter

than in exercises evaluating muscular strength, and fewer repetitions (usually 2-3) are

performed (4). This is in contrast to strength training exercises, where loads used are

typically higher and the number of repetitions are lower (6 or less) (4). A common

method of measuring muscular endurance performance is by using repetitions to

failure (17). Repetitions to failure involve performing sub-maximal force production

in several repetitions until fatigue, and is usually performed with a percentage of 1RM

(17).

Table 1: Volume Assignments Based on Training Load (4)

Training goal

Goal repetitions

Sets*

Strength

≤6

2-6

**Power

Single-effort event

Multiple-effort event

1-2

3-5

Hypertrophy

6-12

3-6

Muscular endurance

≥12

2-3

*These assignments do not include warm-up sets and typically apply to core exercises only.

**The repetition assignments shown for power in this table are not consistent with the %1RM-

repetition relationship. On average, loads equaling about 80% of the 1RM apply to the two- to five-

repetition range.

Vertical Jump Height

The vertical jump (VJ) test is the primary test used to asses muscular power in

the legs (15). There are two forms of the VJ test utilized: the squat jump (SJ) and the

counter-movement jump (CMJ) (15). Both the SJ and CMJ can be performed with or

without the use of arm motions (15). When arm motions are not allowed, subjects are

required to place hands on their hips (15). While the CMJ generally results in higher

jump heights than the SJ, Sayers, et al has argued that SJ is a preferred testing method

due to the variability in CMJ technique as well as the accuracy in calculating peak

power (68).

Caffeine

Intake & Metabolism

Caffeine (1,3,7-trimethylxanthine), found in coffee, tea, soft drinks, and dietary

supplements, is the most used pharmacologically active substance in the world, with

the average American adult consuming 2.4 mg/kg/day (76). Consumption of up to 400

mg (equivalent to 4 mg/kg body weight in a 90 kg person) of caffeine per day has been

determined to be a safe level in adults (35). The average US adult’s coffee

consumption is about two cups per day (about 280 mg of caffeine). In addition,

hundreds of caffeinated beverages exist, ranging from 50 to 500 mg per can or bottle

(equivalent to 0.5-5.5 mg/kg body weight in a 90 kg person) (64).

Caffeine can be absorbed via oral, rectal, or parenteral route, and maximum

blood concentration of caffeine in humans is achieved in one hour after absorption

through the gastrointestinal tract (63). Peak absorption has been determined to be

around 30 minutes in popular products such as colas and coffees, and around 60

minutes in encapsulated forms (44). The half-life of caffeine has a range of 2-12

hours; however, plasma concentration is dependent on time since previous

consumption and other dietary factors, such as fiber (a structural polysaccharide that

resists chemical breakdown by digestive enzymes (1, 29, 33, 51).

Caffeine binds to plasma proteins and is able to distribute freely into

intracellular tissue water, accounting for 10-30 percent of the total plasma pool;

caffeine is also lipophilic and is able to cross the blood-brain barrier (1, 71).

Metabolism of caffeine occurs in the liver through processes of demethylation and

oxidation (33). The primary route of caffeine metabolism is 3-ethyl demethylation to

paraxanthine; this step makes up approximately 75-80 percent of caffeine metabolism

and involves cytochrome P4501A2 (1). Caffeine is also metabolized to theophylline

and theobromine, however metabolism to paraxanthine is the primary metabolic

pathway (1). Caffeine is also reabsorbed by the renal tubules, however only a small

amount of caffeine is excreted in urine unchanged (1). Repeated ingestion of caffeine

does not alter absorption or metabolism of caffeine (28). Research does suggest

menstrual cycles or use of oral contraceptives may alter caffeine clearance (43).

Physiology

Caffeine is both water and fat soluble, which allows distribution to all tissues

of the body (1, 2, 54, 71, 73). As a result, a specific mechanism of action in regards to

exercise performance has yet to be chosen (73). There are several principle

mechanisms that have been proposed to explain the ergogenic potential of caffeine

during exercise: 1) increased myofilament affinity for calcium and/or the increased

release of calcium from the sarcoplasmic reticulum (SR) in skeletal muscle; 2) cellular

action caused by the accumulation of cyclic-3’-5’-adenosine monophosphate (cAMP)

in tissues such as skeletal muscle and adipocytes; 3) cellular actions mediated by the

competitive inhibition of adenosine receptors in somatic cells and the central nervous

system (19). Additionally, early research by Powers et al. suggest that the ergogenic

effects of caffeine in aerobic exercise is related to an increase in fatty acid oxidation,

leading to the sparing of muscle glycogen (62). Increased oxidation of fatty acids

inhibits glycogen phosphorylase activity, switching the preference from glycogen to

fat (60, 67). This resulting increase in free fatty acids is hypothesized to decrease

cellular lactic acid production, a pathway that has been linked to fatigue during heavy

exercise (62). Recent research, however, has found little evidence to support the

hypothesis that caffeine has ergogenic effects due to enhanced fat oxidation (31).

Graham, et al conclude individuals may respond differently to the effects of caffeine,

which could be explained by genetic variations (31). Further potential mechanisms are

described below.

Caffeine may reduce the excretion of calcium (Ca

) that occurs during

exercise (30). Tallis, et al performed a review of numerous isolated muscle studies

examining the direct effects of caffeine (73). Results showed a greater release of Ca

into the intramuscular space, increased myofibrillar Ca

sensitivity, slowing of the

sarcoplasmic reticulum Ca

pump and increased SR Ca

permeability (73). This

combination of events significantly modified the performance of skeletal muscle, most

notably by increasing muscle relaxation time (73). However, Tallis et al concluded

that caffeine’s ability to cause significant improvements in muscle contractility is

likely a result of a number of synergistic effects, and less likely a single mechanistic

action (73).

Another proposed role of the ergogenic effect of caffeine involves calcium and

phosphodiesterase inhibition (17). In vitro studies have shown that caffeine inhibits

phosphodiesterase enzymes, allowing an increase in cAMP (17, 25). An increase in

cAMP, along with an increase in blood catecholamines (such as epinephrine), results

in the activation of hormone sensitive lipase (34). The resulting free fatty acids are

mobilized from the cell membrane of the adipocyte and are transported to tissues and

are oxidized for energy (34). However, this mechanism is unlikely to explain the

ergogenic effect of caffeine observed during athletic activity; while in vitro studies

have demonstrated inhibitory effects on phosphodiesterase, in vivo studies would

require toxic doses of caffeine to observe a physiological benefit (17).

Arguably the most favored mechanism of action involves caffeine’s ability to

inhibit adenosine receptors (36). Adenosine, a molecule similar in structure to caffeine

has been shown to enhance pain perception, induce sleep, and reduce arousal, among

other functions (12, 41, 72). Caffeine, which has a nonselective affinity to adenosine

receptors, can bind to adenosine receptors in the brain and peripheral tissues (26). The

resulting inability of adenosine to bind to receptor sites prevents the adenosine-

induced suppression of dopamine release (17). This contributes to the reported

increase in arousal and alertness frequently associated with caffeine intake (55). As a

result, it is believed that the main mechanism of action is inhibitory effects on

adenosine modifying pain perception while sustaining motor unit firing rates, resulting

in an ergogenic effect (17).

Caffeine ingestion before exercise may cause the undesired effect of an

increase in the inflammatory response, demonstrated by increases in markers of

muscle damage and leukocyte cells (6, 75). As a result, an additional mechanism that

may aid in the ergogenic effect of caffeine involves creatine kinase (CK), a

physiological marker that indicates muscle damage and is associated with higher

levels of pain perception after acute episodes of resistance exercise (48). Creatine

kinase de-phophorylates creatine phosphate to enable rapid phosphorylation of ADP to

ATP for quick, intense muscle contractions (24). Previous literature suggests

resistance exercise results in an increase in CK concentrations (37, 48). Additionally,

other researchers have found that caffeine causes an increase in circulating

catecholamines, such as epinephrine and norepinephrine, which are responsible for the

increase in leukocytes frequently observed post-exercise (11). Bassini-Cameron et al.

hypothesized the fatigue delaying effect of caffeine may even enhance the extent of

muscle damage occurring during intense exercise, as subjects can potentially perform

a higher volume of work following acute caffeine ingestion (6). However, this does

not explain the potential ergogenic effect during exercise, but instead addresses

muscle injury, and related muscle soreness, post-exercise. A study employing caffeine

equivalent to 4.5 mg/kg BW found that an acute ingestion prior to resistance exercise

does not appear to cause greater muscle cell injury, as CK and leukocytes observed

were not above levels that occurred in resistance exercise alone (48). Furthermore,

peak blood levels of CK and associated muscle soreness do not occur until 24 and 48

hours post-exercise (56). Recent literature shows caffeine ingestion before resistance

training may result in lower levels of soreness 2 and 3 days post-exercise (37). This

suggests that the potential negative effect caffeine may have on increasing CK and

leukocyte concentrations during exercise may be outweighed by both the ergogenic

effect frequently observed during exercise as well as the reduced muscle soreness

observed within the following days post-exercise.

Additional Effects of Caffeine

Caffeine has been noted to have multiple effects in the body. Caffeine acutely

raises blood pressure as a result of sympathetic system stimulation and the

antagonistic effect on adenosine (26, 69). These effects on the cardiovascular system

generally return to baseline after 10-60 hours, depending on the amount of caffeine

ingested (33). Both mood and cognitive ability improve following both acute and

chronic caffeine consumption (26). Furthermore, caffeine has been shown to increase

alertness and ability to concentrate, and has long been used to treat headaches due to

its synergistic effects with analgesics; as a result, caffeine is an ingredient used both

alone or in conjunction with other medications, such as acetaminophen (9, 26, 47, 69).

Persons who abstain from caffeine overnight (8-12 hours) have a significant depletion

of caffeine by early morning; as a result, subjects are more sensitive to the stimulant

effects upon reintroduction into the body (66).

Caffeine’s impact on athletic performance has been investigated in a range of

athletic exercises, including endurance events, team sports, and high-intensity, short-

duration activities (3, 23, 24, 39, 57). Due to the observed effects of caffeine, the

World Anti-Doping Agency has caffeine placed on the 2015 monitoring program (79).

While there is no restriction set to the amount of caffeine to be consumed prior to an

athletic event, caffeine concentration is monitored for potential repetitive misuse (10,

40, 79). Previously, the International Olympic Committee (IOC) prohibited urinary

caffeine concentrations in excess of 12 mcg/mL (52). This currently unrestricted limit

of caffeine can allow athletes to consume amounts of caffeine associated with

ergogenic benefits prior to athletic events. In a meta-analysis of caffeine studies

examining various types of physical activity performance, the amount of caffeine

commonly shown to improve endurance is between 3 and 6 mg/kg of body mass,

consumed no more than 60 minutes before activity (27).

Considering the multiple proposed mechanisms of caffeine, the remaining

sections of the literature review will review the effects of caffeine in aerobic and

anaerobic athletic performance.

Aerobic Performance

The effects of caffeine on aerobic performance have been investigated

extensively in aerobic exercises, particularly in running, cycling, and rowing. Several

meta-analysis report that caffeine has an ergogenic effect on aerobic performance (20,

27). Doherty, et al (20) reviewed 40 double-blind studies evaluating a combination of

cycling, running, and rowing exercises in subjects with mixed reported habitual

caffeine intakes; the consensus was that 3-10 mg/kg of caffeine is necessary to have a

positive impact on exercise performance. Compared to placebo, caffeine improved test

outcomes by 12.3% on average (20). Ganio, et al (27) presented lower findings, citing

a mean improvement of 4.4+5.0% in 21 cycling trials, 0.9+0.7% in 6 running trials,

and 1.1+0.3% in 4 rowing trials. Ganio, et al determined that quantities above 3 mg/kg

are needed for improvement and that athletes consume up to 6 mg/kg no more than 60

minutes before exercise (27).

Desbrow, et al (18) compared the ergogenic effects of two different dosages of

caffeine, 3 mg/kg and 6 mg/kg, to placebo in 16 well-trained male cyclists. In this

randomized, double-blind study, participants performed cycling ergometer time trials

after receiving either 3 or 6 mg/kg of caffeine or placebo (18). Both treatments had

significant enhancements in endurance cycling, with 4.2% enhancement in the low

dose (3 mg/kg) treatment and 2.9% in the high dose (6 mg/kg) treatment (18). The

authors concluded that greater levels of circulating caffeine from higher dosages do

not equate to better performance outcomes (18).

In a double-blind crossover study performed by Bruce, et al, eight competitive

male rowers completed three trials of a 2000-m rowing test, each one hour after

consuming either 6 or 9 mg/kg BW of caffeine or placebo (16). Both 6 and 9 mg/kg

BW caffeine led to an improvement in 2000-m simulated rowing time trial

performance (16). The 6 mg/kg and 9 mg/kg caffeine treatments had similar

improvements in performance; however, one-third of the subjects had urinary caffeine

concentrations at or above 12 mcg/L when they received 9 mg/kg BW caffeine, which

exceeds the limit set by the IOC (10, 16). As a result, Bruce, et al recommends

utilizing trial doses of caffeine equivalent to ~6 mg/kg for competitive male athletes

(16).

In a double-blind, placebo-controlled trial performed by O’Rourke et al, 15

recreational and 15 well-trained runners (gender was undisclosed) completed two 5

kilometer time-trials following ingestion of either 5 mg/kg caffeine or placebo (58).

The caffeine treatment had significant improvements in performance in both

recreational and well-trained groups (1.0% and 1.1%, respectively) (58). However, the

authors questioned the practical significance of the results, citing a small beneficial

effect (58).

Paton, et al utilized a dose of 6 mg/kg caffeine or placebo in a randomized,

double-blind, crossover experiment with 16 male team-sport athletes (59). Subjects

performed 10 sets of 10-second sprints, with each sprint followed by 10 seconds of

rest (59). The observed effect of caffeine was not significant in sprint performance and

on fatigue; in fact, the caffeine treatment was found to have a slight decrease in agility

(59).

Despite the extent of which the effect of caffeine has in aerobic performance, a

specific recommendation on dosage has yet to be determined. Based on two meta-

analyses, a wide range of dosage recommendations are proposed: Doherty, et al

propose an effective range of 3-10 mg/kg, while Ganio, et al offers an arguably

smaller range of 3-6 mg/kg (20, 27). In the research performed by Desbrow, et al, it

was concluded that higher doses of caffeine do not equate to better performance, while

Bruce, et al concluded that doses of 6 mg/kg and 9 mg/kg resulted in similar

performance, but the latter dose exceeded limits set by the IOC (16, 18). Despite the

variability in dosing amongst studies, the general consensus among meta-analyses is

that dosage of caffeine no more than 60 minutes prior to exercise may provide

ergogenic benefits, however dosage amounts are to be further investigated on an

individual level that accounts for multiple factors, such as subject habituation,

ingestion timing, and ingestion mode (capsule versus liquid, for example) (27). Ganio

et al. also recommend that subjects abstain from caffeine for 7 days before use to give

caffeine the greatest chance of optimizing the ergogenic effect (27).

Anaerobic Performance

Similarly to aerobic performance, the effects of caffeine supplementation in

anaerobic exercise have been reviewed at length. However, testing methods chosen in

anaerobic testing have been less consistent, partially because anaerobic performance

can be more difficult to quantify (30). A review of the literature indicates uncertainty

towards whether the perception of athletic improvement is related to maximum

strength, power, or rate of fatigue (30).

Conflicting results have been found in the literature regarding caffeine and

1RM. Beck et al examined 1RM for bench press and leg extension exercises in 37

resistance-trained males (7). A significant improvement was found in bench press

1RM but not in the leg extension (7). However, Williams et al and Astorino et al both

failed to find and effect for 1RM in the bench press and leg press in 9 resistance-

trained men with a mean of 4.2 years experience and in 22 resistance-trained males,

respectively (3, 77). This inconsistency in results suggests that further research is

required before a definitive conclusion can be made.

Duncan, et al (23) conducted a double-blind, randomized crossover study

involving 9 males and 2 females with specific experience in performing resistance

exercise and were actively participating in greater than ten hours per week of

programmed strength and conditioning activities. Each subject was provided placebo

or 5 mg/kg of caffeine and tested in randomized order for number of repetitions to

failure, rating of perceived exertion (RPE) and perception of muscle pain during

resistance exercise (23). All subjects were competent in techniques performed in the

study, including bench press, deadlift, prone row, and back squat exercises (23).

Subjects were asked to refrain from vigorous exercise and to maintain normal dietary

patterns for the 48 hours prior to testing, and were asked to cease caffeine use from

6:00 pm the night before testing (23). In the caffeinated condition, subjects had a

lower RPE and muscle pain perception compared to the placebo condition. This study

determined that caffeine ingestion did not enhance performance in number of

repetitions, but did reduce perception of exertion and muscle pain (23).

A power trial performed by Doherty et al evaluated the effect of moderate-dose

caffeine on performance during high-intensity cycling (21). Eleven trained male

cyclists recruited from local cycling clubs were recruited for this double-blind,

randomized, crossover study where they received caffeine equivalent to 5 mg/kg BW

or placebo and participated in a ramp test designed to exhaust participants in 10-12

minutes (21). Mean power output was significantly greater in the caffeine treated

group compared to placebo. Additionally, blood lactate was significantly higher in the

caffeine treatment group compared to placebo (21). This was hypothesized to be one

of the mechanisms that allowed the caffeine treatment group to perform at a higher

intensity than the placebo group (21).

Lorino et al. (46) evaluated the effect of caffeine on agility, another measure of

anaerobic performance. Agility is a skill that involves speed and reaction time as well

as other performance skills. In this study, 17 males consumed placebo or 6 mg/kg BW

caffeine in randomized order and performed a proagility run test and 30-second

Wingate test (a common test used for anaerobic power) (46). Results showed that

caffeine did not improve agility or power output in young, recreationally active males

who are not habituated to caffeine (46). In a similar manner, Bell et al. (8) examined

the impact of caffeine alone and combined with ephedrine in 16 untrained males

through use of a 30-second Wingate test. Like the study by Lorino et al, caffeine did

not improve anaerobic power, suggesting that caffeine does not improve the anaerobic

parameters of power and agility in recreationally trained athletes (8, 46).

Another double-blind, randomized, crossover study by Astorino et al (3),

evaluated 22 resistance-trained men who completed total-body resistance training a

minimum of two days per week. Recruited subjects ingested either 6 mg/kg BW of

caffeine or a placebo and performed repetitions to failure on both the barbell bench

press and leg press using 60% of their determined maximal lifting ability (1RM) (3).

Subjects refrained from caffeine intake for 48 hours and strenuous exercise for 24

hours before each visit. There was no significant effect of caffeine on muscular

strength or endurance, determined as complete number of repetitions to failure, in

subjects when consuming caffeine when compared to placebo when a dosage of 6

mg/kg BW was used (3).

In another crossover study, twenty elite male athletes performed knee extensor

and flexor exercises (39). Subjects recruited were intercollegiate Division I varsity

American football team members. Exclusion criteria included high daily caffeine

consumption (defined as >100 mg/day) or lacking sufficient weight training

experience (defined as less than two years). Subjects were required to abstain from

exercise for 48 hours and from caffeine for one week prior to testing (39). A

significant increase in muscular power was noted in subjects when they ingested

capsules containing 7 mg/kg BW, compared to placebo (39).

Woolf, et al (78) performed a randomized crossover study examining the effect

of 5 mg/kg BW of caffeine in 17 collegiate football athletes. All participants recruited

were considered low caffeine users, with a reported average intake of 16+20 mg/day

(78). Participants ingested either caffeine or placebo beverage with a small meal and

completed three exercise tests: a 40-yard dash, 20-yard shuttle, and bench press until

fatigue using either 185 or 225 pounds, with the lower weight used for participants

who were unable to bench 225 pounds (78). No differences were found between

treatments for any of the three exercise tests; however, 59% of the participants

improved in performance with caffeine with the bench press and 40-yard dash (78).

Unlike other studies, which use 60% of participant’s calculated 1RM for testing

purposes, this study chose a standardized weight, regardless of each subject’s

individual ability (3, 78).

In a study by Bloms et al, 25 male and female NCAA Division I collegiate

athletes participating in 8-20 hours of training per week were recruited to asses squat

jump (SJ) height following ingestion of caffeine equivalent to 6 mg/kg BW (13).

Caffeine ingestion had a positive significant effect (p=0.001) in SJ height, with an

improvement of 5.4+6.5% (13). Of the 16 males enrolled, 9 were identified as

responders during the SJ; 78% (7/9) of these subjects who responded to caffeine were

identified as habitual consumers (13). Bloms et al. concluded that a dosage of 5 mg/kg

of caffeine may positively impact performance in ballistic tasks such as the vertical

jump (13). However, the authors note that all subjects recruited were Division I

athletes, and that results may not be generalizable to lower-level athletes and the

general population (13).

Plaskett, et al performed a randomized, double-blind, repeated measures

experiment evaluating a dose of 6 mg/kg in 15 males (61). Subjects performed

repeated submaximal contractions of the right quadriceps one hour after ingestion of

either caffeine, placebo, or no capsule (61). Results of the study concluded that

caffeine increased muscular endurance in repeated submaximal isometric contractions

in the quadriceps (61). In this study, all subjects were non-habitual caffeine users,

defined as those who reportedly consumed less than 200 mg of caffeine/wk (61).

Furthermore, this study did not define the current resistance training status of its

participants (61).

Duncan, et al evaluated bench press repetitions to failure in 13 moderately

resistance trained men (22). Participants in his study consumed 5 mg/kg caffeine or

placebo and performed bench press repetitions to failure using 60% 1RM (22).

Participants completed significantly more repetitions to failure and lifted significantly

greater weight with the caffeine treatment compared to placebo (22). However, RPE

was not significantly different between groups (22). Subjects recruited were all active

participants in University team sports, including rugby, football, and basketball, and

have been competing in their sport for a mean time of 10.4+2.3 years (22). As a result,

the results of this study are likely not generalizable to a broader audience, such as

recreational athletes.

Discrepancies in the literature exist regarding caffeine’s potential ergogenic

effect on anaerobic performance. However, this variability can be due to a number of

factors, including testing procedures, caffeine administration dose, subject caffeine

habituation, and subject strength training experience. Previous studies have provided

subjects with varying amounts of caffeine using similar crossover designs (3, 23, 39,

78). While the amount of caffeine provided varied based on the study, the method of

determining the amount was based on a standard equation of milligrams per kilogram

of actual subject (mg/kg body weight) (3, 23, 39). Results from the studies performed

by Duncan et al (23), Astorino et al (3), and Jacobson et al (39) suggest that 7 mg/kg

of BW is an effective dosage to experience a significant change in performance in

strength training exercises. As a result, our proposed study also utilizes a caffeine

dosage of 7 mg/kg BW.

Conclusions

As previously stated, muscle endurance is commonly measured using

repetitions to failure with weights equivalent to a percentage of an individual’s 1RM

(17). Currently, information published in the literature on resistance training variables

is insufficient in terms of concluding whether or not caffeine has an ergogenic effect

on resistance training variables, such as muscle endurance, in recreationally trained

athletes, as a majority of the literature recruits participants at the collegiate athletic or

above level. Additionally, to our knowledge, there is limited research comparing

caffeine’s effects for resistance training between habitual and non-habitual caffeine

users. Therefore, in our study, we ask recreationally trained athletes to perform a

combination of resistance exercises incorporating large muscle groups in both upper

and lower body – bench press repetition to failure, squat repetitions to failure,

isometric force plate, and vertical jump - while ingesting a dose of caffeine equivalent

to 7 mg/kg BW.

Currently, research of the potential effect of caffeine on muscular endurance

has been performed on subjects demonstrating elite athletic ability (3, 39). Less

research has been performed on the impact of acute caffeine ingestion on strength and

endurance in the average individual who participates in light to moderate consistent

physical activity. Our primary hypothesis is that acute caffeine ingestion in the amount

of 7 mg/kg BW will increase the number of bench press repetitions to failure

compared to placebo ingestion in college age, recreational male athletes. Our

secondary hypothesis is that acute ingestion of caffeine will also increase the number

of squat repetitions to failure, increase the amount of force generated from a vertical

jump and isometric squat exercise, and decrease rating of perceived exertion at the

time of testing, when compared to placebo ingestion.

Furthermore, previous studies have not taken body composition into

consideration (3, 23, 39). Our exploratory hypothesis is that subjects with lower body

fat percentage will demonstrate a significant increase in repetitions to failure in bench

press and squat exercises when ingesting caffeine when compared to subjects with a

higher body fat percentage. To determine this, body fat percentage will be collected

prior to testing. As an additional exploratory hypothesis, we believe rating of

perceived exertion will be decreased in subjects when ingesting caffeine

supplementation compared to placebo.

Appendix 2: Consent Form

Subject Consent Form for Research

The University of Rhode Island

Department of Kinesiology

Kingston, RI 02881

The Effect of Caffeine on Muscular Endurance and

Power in College Male Athletes

You are being invited to take part in a research project described below. The

researcher will explain the project to you in detail. You should feel free to ask

questions. If you have more questions later, Dr. Kathleen Melanson, the person

mainly responsible for this study, (Phone 401-874-4477); Dr. Disa Hatfield, a co-

investigator in the Kinesiology department, (Phone 401-874-5183); or Dr. Kelly

Matson, a co-investigator in the Pharmacy department, (Phone 401-874-5811), will

discuss them with you. You must be at least 18 years old to be in this research project.

Description of the project:

You have been asked to take part in the study that tests the potential effect of a high

caffeine dosage on muscular endurance and power.

What will be done:

1. Height, weight, and 1-repetition maximum (the maximum amount of weight that

can be moved with one repetition) estimates will be taken.

2. The study will consist of two test days, one week apart, where you will perform

repetitions with weights equal to approximately 60% of your respective 1-repetition

maximum until failure in two exercises (Smith machine squat and bench press).

3. 24-hours prior to the test day, subjects are asked to abstain from consuming

caffeine-containing products.

4. On the test day, a capsule(s) containing either a placebo or a pre-made caffeine

supplement equal to 7 milligrams per kilogram of body weight will be provided to the

subject for consumption (for example, if a subject weighs 75 kilograms, they will

ingest capsules equivalent to 525 milligrams of caffeine). Twelve fluid ounces of

water will be provided to aid in pill ingestion.

5. Subjects will remain stationary to allow absorption for one hour after consuming the

pill(s).

6. A brief questionnaire will be provided to be completed throughout the testing

process.

7. The following tests will be performed:

• Bench press to failure using weight equivalent to 60% of the 1-repetition

maximum weight (calculated from the bench press value obtained during the

first visit)

• Smith machine squat to failure using weight equivalent to 60% of the 1-

repetition maximum weight (calculated from the leg press value obtained

during the first visit)

• Force plate test

• Vertical jump test

8. Subjects are to consistently keep a log for three days following the test procedure.

No dietary restrictions will be in place at this time; however, 24-hours prior to the

second test day, subjects will be asked to abstain from caffeine-containing products.

9. One week later, subjects will return to perform the same procedure, consuming the

alternative capsule(s). Throughout the study, both the subject and the researchers will

be unaware as to whether you have consumed the caffeine capsule(s) or the placebo

until after all testing has been completed.

Risks or discomfort:

Caffeine is a stimulant, and this test involves the consumption of a significant dosage

of caffeine. While the amount consumed is well within the safe limit, there is a risk of:

increased blood pressure, reduced control of fine motor movements, and risk of

insomnia. Risk is greater in non-habitual consumers. Caffeine withdrawal can also

produce headache, fatigue, and decreased alertness. In addition, caffeine has been used

as a diuretic, which can be detrimental to athletes performing in long-term endurance

events.

In addition to caffeine use, there is risk of injury in performing any form of strength

training exercises. This study requires testing for 1-repetition maximum and

performing repetitions to failure in different muscle groups.

The amount of caffeine used in this study is well within the safe limits of consumption

for healthy, adult males. In addition, many previous studies testing the effect of

caffeine on healthy adults during physical activity have incorporated caffeine with

doses at and exceeding the dosage used in this study (7 milligrams of caffeine per

kilogram of body weight). In order to maintain safety of all subjects, the following

criteria warrants exclusion from the study: those with diagnosed high blood pressure,

known or suspected allergies/negative reactions to caffeine, and/or known or

suspected heart conditions.

Benefits of this study:

Although there will be no direct benefit to you for taking part in this study, the

researcher may learn more about caffeine supplementation in regards to strength

athletes. Currently, there is significant data to demonstrate the benefit of caffeine

consumption prior to cardiorespiratory endurance activities (running, cycling).

However, little data is currently available in regards to muscular strength/endurance.

Confidentiality:

Your participation in this study is strictly confidential. None of the results or collected

data will identify you by name. All records will be stored in a locked cabinet and

viewed solely within the Energy Balance Lab located in Fogarty Hall. Data entered in

any computer programs will not contain information identifiable back to you. Please

note, all data is subject to inspection by federal, state, and local agencies, such as the

Food and Drug Administration (FDA).

In case there is any injury to the subject: (If applicable)

In the event of an injury during the testing process, the URI emergency medical

services will be contacted at (401)-874-5255. If this study causes you any injury, you

should write or call the office of the Vice President for Research, 70 Lower College

Road, University of Rhode Island, Kingston, Rhode Island, telephone: (401) 874-

4328.

Decision to quit at any time:

Participation in this study is up to you. You are in no way required to participate. If

you decide to take part in the study, you may quit at any time. Whatever you decide

will in no way be recorded, penalize you, affect enrollment status and/or grades. If you

wish to quit, you simply inform the lab (Fogarty 205, phone 401-874-2067) of your

decision.

Rights and Complaints:

If you are not satisfied with the way this study is performed, you may discuss your

complaints with Dr. Kathleen Melanson (401-874-4477), Dr. Disa Hatfield (401-874-

5183), or Dr. Kelly Matson (401-874-5811) anonymously, if you choose. In addition,

you may contact the office of the Vice President for Research, 70 Lower College

Road, Suite 2, University of Rhode Island, Kingston, Rhode Island, telephone: (401)

874-4328.

You have read the Consent Form. Your questions have been answered. Your

signature on this form means that you understand the information and you agree to

participate in this study.

____________________________________________________________________

residing at

________________________________________________(zip)_________

telephone _________________________ age _________ (date of birth)

____________

agree to participate in this research project.

____________________________ ____________________________

Signature of subject Signature of Researcher

____________________________ ____________________________

Typed/printed Name Typed/printed Name

_______________________ _____________________

Date Date

Please sign both consent forms, keeping one for yourself.

Appendix 3: Study Timeline

Appendix 4: Test Day Timeline

Appendix 5: Pre-Screening Questionnaire

Pre-Screening Questionnaire

How would you describe your weightlifting routine?

0-1 2-3 4-5 5+ (days per week)

How long have you consistently participated in weight-bearing exercise?

<1 month 1-3 months 4-5 months 6-12 months +1 year

Are bench-press exercises incorporated in your typical weight-bearing routine?

yes no

Are leg-press exercises incorporated in your typical weight-bearing routine?

yes no

How would you describe your typical coffee intake (caffeinated)?

0 1 2 3 4 5+ (8 fl oz cups per day)

How would you describe your typical soda intake (caffeinated)?

0 1 2 3 4 5+ (8 fl oz cups per day)

Appendix 6: Personal Health History Questionnaire

Personal Health History Questionnaire

Please complete this as accurately and completely as possible. If you would like

clarification on any question, please feel free to ask.

Name: ____________________________________ Age: ________ Gender

_________

Mailing address: _______________________________________________________

Phone number: _____________________________ Today’s date: ________________

Email address: _____________________________

Approximate weight: _____________________Approximate height:

______________

Ethnic Background (circle one)

• African-American

• Asian-American

• Caucasian

• Hispanic-American

• Other _____________________________

General Medical History Circle One

Do you currently have any medical complaints? Yes No

(please specify) ________________________________________________________

Do you take any prescribed or over-the-counter medication? Yes No

(please specify) ________________________________________________________

Dietary History

Please list any food allergies, intolerances or specific foods you avoid

_____________________________________________________________________

Do you experience caffeine withdrawal symptoms if you do not consume it in the

morning. (i.e., headache)?

__________________________________________________

Are you able to abstain from alcohol consumption for several days in a row?

____________________________________________________________________

Please describe your diet history. Make sure to specify if you are or have been

vegetarian, if you are or have been on a self-prescribed or medical-prescribed special

diet, or if you have participated in bingeing, crash diets, cyclic dieting, or were

anorexic and/or bulimic:

_________________________________________________________

The following questions address body weight history.

What is the length of time you have maintained your present weight? _____________

How much would you like to weigh? ________________________

How many times has your weight fluctuated by at least 5 lbs in the last year? _______

Please describe any long-term weight changes you have experienced (e.g., lost 50 lb.

in 1995):______________________________________________________________

How would you describe the typical weight of your parents over the last few years?

Under-weight Just right Over-weight Obese Unknown

Your Mother O O O O O

Your Father O O O O O

General History: Have you had or do you have:

Adrenal disease Yes No

Hypoglycemia (low blood sugar) Yes No

Seizures Yes No

Kidney or bladder problems Yes No

Stomach ulcers Yes No

Diabetes Yes No

Family history of diabetes Yes No

Thyroid Diseases Yes No

Any chronic illness that might cause weight loss Yes No

Atrial Fibrillation (irregular heart rate) Yes No

Tachycardia (fast heart rate) Yes No

Other Yes No

Explain any Yes responses:

_______________________________________________

Do you have any close blood relatives have or had type 2 diabetes (parents,

grandparents, siblings, aunts or uncles)? Yes No

Do you have any close blood relatives have or had heart disease? Yes No

Appendix 7: Caffeine Frequency Questionnaire

Subject ID: ______________________ Date: ___________________

CAFFEINE FREQUENCY QUESTIONNAIRE (CFQ)

Please answer the following questions as completely and honestly as you can. This

information is STRICTLY CONFIDENTIAL - do not write your name anywhere on

this page.

Select the box next to each item that best describes your usual intake. Consider intake

over the course of the past calendar year.

Never

Monthly

Weekly

serving/

day

serving

/day

serving/

day

COFFEE

Brewed, generic

Brewed, decaf

Espresso

Espresso decaf

TEAS

Brewed

Snapple

Nestea

Arizona Iced

SOFT

DRINKS

Coca-Cola

Diet Coca-Cola

Dr. Pepper

Diet Dr. Pepper

Pepsi

Diet Pepsi

Root Beer

Diet Root beer

Sierra Mist

Sprite

Never

Monthly

Weekly

serving

/day

serving

/day

serving

/day

ENERGY

DRINKS

Monster

Full Throttle

Red Bull

Vitamin Water

Amp

5 Hour energy

FROZEN

DESSERTS

Ben & Jerry’s

Coffee ice cream

Starbucks coffee

ice cream

CHOCOLATE

Hershey’s

chocolate

Hershey's Dark

chocolate

Hershey's kisses

Hot cocoa (5 oz)

MEDICATIONS

Vivarin

NoDoz

Excedrin

Vanquish

Anacin

Dristan

Dexatrim

Appendix 8: Borg CR-10 Scale of Perceived Exertion

Borg CR-10 Scale of Perceived Exertion

Nothing at all

0.3

0.5

Extremely weak

Just noticeable

0.7

Very weak

1.5

Weak

Light

2.5

Moderate

Strong

Heavy

Very strong

Extremely strong

“Maximal”

Absolute maximum

Highest possible

Appendix 9: Additional Tables and Figures

Table 2: Correlations Between Exercise Performance with Caffeine Based on

Lean Body Mass and Self-Reported Habitual Consumption

mg/kg LBM

Habitual

consumption

Bench Press repetitions

Squat repetitions

Caffeine

∆ Treatments

Caffeine

∆ Treatments

R p

.020

.924

.065

.762

-.031

.887

.297

.159

.186

.384

.193

.366

-.016

.939

.003

.989

Pearson correlations used. No significant correlations found. Lean body mass calculated by subtracting

fat mass from total body mass.

Table 3: Mean±SD of RPE Before and After Bench Press and Smith Machine

Squat Tests with Caffeine and Placebo Treatments

Caffeine

Placebo

Pre

Post

Pre

Post

Bench Press

(n=21*)

2.3±1.9

5.5±1.9

2.6±1.6

5.9±1.9

0.360

Squat

(n=23)

1.5±1.3

5.9±1.6

1.9±1.5

6.1±2.1

0.196

2x2 Repeated Measures ANOVA used. No significance between treatments in either bench press or

squat.

*2 subjects omitted due to missing data

Figure 4: Relationship Between 1RM Squat and 1RM Bench

y!=!0.762 x!+!10.854

R²!=!0.57253

100

150

200

250

300

350

100 150 200 250 300 350 400

1RM!BENCH

1RM!SQUAT

Figure 5: Proportion of Subjects Receiving Varying Dosages of Caffeine Based on

Lean Body Mass

Mean (±SD) dosage received based on total body mass (mg/kg): 7.0±0.1

Mean (±SD) dosage received based on lean body mass (mg/kg): 8.3±0.7

7.0 to 7.9

39%

8.0 to 8.9

35%

9.0+

26%

Figure 6: Difference in Individual Number of Bench Press Repetitions to Failure

in Subjects Identified as Low Caffeine Consumers

Low caffeine consumer defined as ≤8oz of caffeine containing product/day, as

determined by self-reported caffeine frequency. (n=15)

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Figure 7: Difference in Individual Number of Bench Press Repetitions to Failure

in Subjects Identified as High Caffeine Consumers

High caffeine consumer defined as >8oz of caffeine containing product/day, as

determined by self-reported caffeine frequency. (n=8)

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Figure 8: Difference in Individual Number of Smith Machine Squat Repetitions

to Failure in Subjects Identified as Low Caffeine Consumers

Low caffeine consumer defined as ≤8oz of caffeine containing product/day, as

determined by self-reported caffeine frequency. (n=15)

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Figure 9: Difference in Individual Number of Smith Machine Squat Repetitions

to Failure in Subjects Identified as High Caffeine Consumers

High caffeine consumer defined as >8oz of caffeine containing product/day, as

determined by self-reported caffeine frequency. (n=8)

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Appendix 10: Flyer

BIBLIOGRAPHY

1.# Arnaud#MJ.#The#pharmacology#of#caffeine.#Prog%Drug%Res#31:#273-313,#

1987.#

2.# Arnaud#MJ.#Metabolism#of#caffeine#and#other#components#of#coffee.#1993.#

3.# Astorino#TA,#Rohmann#RL,#Firth#K.#Effect#of#caffeine#ingestion#on#one-

repetition#maximum#muscular#strength.#Eur%J%Appl%Physiol#102:#127-132,#

2008.#

4.# Baechle#T,#Earle#R.#Essentials%of%Strength%Training%and%Conditioning.#

Champaign,#IL,#2008.#

5.# Ball#TE,#Rose#KS.#A#field#test#for#predicting#maximum#bench#press#lift#of#

college#women.#J%Appl%Sport%Sci%Res#5:#169-170,#1991.#

6.# Bassini-Cameron#A,#Sweet#E,#Bottino#A,#Bittar#C,#Veiga#C,#Cameron#LC.#

Effect#of#caffeine#supplementation#on#haematological#and#biochemical#

variables#in#elite#soccer#players#under#physical#stress#conditions.#Br%J%

Sports%Med#41:#523-530,#2007.#

7.# Beck#TW,#Housh#TJ,#Schmidt#RJ,#Johnson#GO,#Housh#DJ,#Coburn#JW,#Malek#

MH.#The#acute#effects#of#a#caffeine-containing#supplement#on#strength,#

muscular#endurance,#and#anaerobic#capabilities.#J%Strength%Cond%Res#20:#

506-510,#2006.#

8.# Bell#DG,#Jacobs#I,#Ellerington#K.#Effect#of#caffeine#and#ephedrine#ingestion#

on#anaerobic#exercise#performance.#Med%Sci%Sports%Exerc#33:#1399-1403,#

2001.#

9.# Bigal#ME,#Sheftell#FD,#Rapoport#AM,#Tepper#SJ,#Lipton#RB.#Chronic#daily#

headache:#identification#of#factors#associated#with#induction#and#

transformation.#Headache#42:#575-581,#2002.#

10.# Birkett#DJ,#Miners#JO.#Caffeine#renal#clearance#and#urine#caffeine#

concentrations#during#steady#state#dosing:#implications#for#monitoring#

caffeine#intake#during#sports#events.#Br%J%Clin%Pharm#31:#405-408,#1991.#

11.# Bishop#NC,#Fitzgerald#C,#Porter#PJ,#Scanlon#GA,#Smith#AC.#Effect#of#caffeine#

ingestion#on#lymphocyte#counts#and#subset#activation#in#vivo#following#

strenuous#cycling.#Eur%J%Appl%Physiol#93:#606-613,#2005.#

12.# Bjorness#TE,#Greene#RW.#Adenosine#and#sleep.#Current%

Neuropharmacology#7:#238-245,#2009.#

13.# Bloms#LP,#Fitzgerald#JS,#Short#MW,#Whitehead#JR.#The#effects#of#caffeine#on#

vertical#jump#height#and#execution#in#collegiate#athletes.#J%Strength%Cond%

Res,#2015.#

14.# Borg#GA.#Human%Kinetics:%Borg's%perceived%exertion%and%pain%scales.#

Champaign,#IL,#1998.#

15.# Brown#LE,#Weir#JP.#ASEP#procedures#recommendation#i:#accurate#

assessment#of#muscular#strength#and#power.#J%Exercise%Physiology#4:#1-21,#

2001.#

16.# Bruce#CR,#Anderson#ME,#Fraser#SF,#Stepto#NK,#Klein#R,#Hopkins#WG,#

Hawley#JA.#Enhancement#of#2000-m#rowing#performance#after#caffeine#

ingestion.#Med%Sci%Sports%Exerc#32:#1958-1963,#2000.#

17.# Davis#JK,#Green#JM.#Caffeine#and#anaerobic#performance:#ergogenic#value#

and#mechanisms#of#action.#Sports%Med#39:#813-832,#2009.#

18.# Desbrow#B,#Biddulph#C,#Devlin#B,#Grant#GD,#Anoopkumar-Dukie#S,#Leveritt#

MD.#The#effects#of#different#doses#of#caffeine#on#endurance#cycling#time#

trial#performance.#J%Sports%Sci,#2011.#

19.# Dodd#SL,#Herb#RA,#Powers#SK.#Caffeine#and#exercise#performance:#an#

update.#Sports%Medicine#15:#14-23,#1993.#

20.# Doherty#M,#Smith#PM.#Effects#of#caffeine#ingestion#on#exercise#testing:#a#

meta-analysis.#J%Sports%Nutrition%and%Exercise%Metabolism#14,#2004.#

21.# Doherty#M,#Smith#PM,#Hughes#MG,#Davison#RR.#Caffeine#lowers#perceptual#

response#and#increases#power#output#during # high-intensity#cycling.#J%

Sports%Sci#22:#637-643,#2007.#

22.# Duncan#MJ,#Oxford#SW.#The#effect#of#caffeine#ingestion#on#mood#state#and#

bench#press#performance#to#failure.#J%Strength%Cond%Res#25:#178-185,#

2011.#

23.# Duncan#MJ,#Stanley#M,#Parkhouse#N,#Cook#K,#Smith#M.#Acute#caffeine#

ingestion#enhances#strength#performance#and#reduces#perceived#exertion#

and#muscle#pain#perception#during#resistance#exercise.#Eur%J%Sport%Sci#13:#

392-399,#2013.#

24.# Dunford#M,#Doyle#JA.#Nutrition%for%Sport%and%Exercise.#Belmont,#CA:#Peter#

Adams,#2008.#

25.# Fox#SI.#Human%Physiology,%10th%edition.#New#York,#NY:#McGraw-Hill,#2008.#

26.# Fredholm#BB,#Battig#K,#Holmen#J,#Nehlig#A,#Zvartau#EE.#Actions#of#caffeine#

in#the#brain#with#special#reference#to#factors#that#contribute#to#its#

widespread#use.#Pharmacol%Rev#51:#83-133,#1999.#

27.# Ganio#MS,#Klau#JF,#Casa#DJ,#Armstrong#LE,#Maresh#CM.#Effect#of#caffeine#on#

sport-specific#endurance#performance:#a#systematic#review.#J%Strength%

Cond%Res#23:#315-324,#2009.#

28.# George#J,#Murphy#T,#Roberts#R,#Cooksley#WGE,#Halliday#KW,#Powell#LW.#

Influence#of#alcohol#and#caffeine#consumption#on#caffeine#elimination.#Clin%

Exp%Pharmacol%Physiol#13,#1986.#

29.# Gilbert#RM.#Caffeine%consumption.%In%the%methylxanthine%beverages%in%foods:%

chemistry,%consumption,%and%health%effects.,#1984.#

30.# Graham#TE.#Caffeine#and#exercise:#metabolism,#endurance#and#

performance.#Sports%Med#31:#785-806,#2001.#

31.# Graham#TE,#Battram#DS,#Dela#F,#El-Sohemy#A,#Thong#FS.#Does#caffeine#alter#

muscle#carbohydrate#and#fat#metabolism#during#exercise?#Applied%

Physiology,%Nutrition,%and%Metabolism#33:#1311-1318,#2008.#

32.# Harris#GR,#Stone#MH,#Obryant#HS,#Proulx#CM,#Johnson# RL.#Short-term#

performance#effects#of#high#power,#high#force,#or#combined#weight-

training#methods.#J%Strength%Cond%Res#14,#2000.#

33.# Hartley#TR,#Sung#BH,#Pincomb#GA.#Hypertension#risk#status#and#effect#of#

caffeine#on#blood#pressure.#Hypertension#36:#137-141,#2000.#

34.# Harvey#RA,#Ferrier#D.#Biochemistry,%5th%edition.#Baltimore,#MD:#Lippincott#

Williams#&#Wilkins,#2011.#

35.# Heckman#MA,#Weil#J,#Gonzalez#de#Mejia#E,.#Caffeine#(1,3,7-

trimethylxanthine)#in#foods:#a#comprehensive#review#on#consumption,#

functionality,#safety,#and#regulatory#matters.#J%Food%Sci#75:#R77-87,#2010.#

36.# Holtzman#SG,#Mante#S,#Minneman#KP,#.#Role#of#adenosine#receptors#in#

caffeine#tolerance.#J%Pharmacol%Exp%Ther#256:#62-68,#1991.#

37.# Hurley#CF,#Hatfield#DL,#Riebe#DA.#The#effect#of#caffeine#ingestion#on#

delayed#onset#muscle#soreness.#J%Strength%Cond%Res#27:#3101-3109,#2013.#

38.# Invergo#JJ,#Ball#TE,#Looney#M.#Relationship#of#push-ups#and#absolute#

muscular#endurance#to#bench#press#strength.#J%Appl%Sport%Sci%Res#5,#1991.#

39.# Jacobson#BH,#Weber#MD,#Claypool#L,#Hunt#LE,.#Effect#of#caffeine#on#

maximal#strength#and#power#in#elite#male#athletes.#Br%J%Sp%Med#26:#276-

280,#1992.#

40.# Jenkinson#DM,#Harbert#AJ.#Supplements#and#sports.#Am%Fam%Physician#78:#

1039-1046,#2008.#

41.# Kalmar#JM.#The#influence#of#caffeine#on#voluntary#muscle#activation.#Med%

Sci%Sports%Exerc#37:#2113-2119,#2005.#

42.# Knudson#D.#Fundamentals%of%biomechanics,%2nd%edition.#New#York,#NY:#

Springer#Science,#2007.#

43.# Lane#JD,#Steege#JF,#Rupp#SL,#Kuhn#CL.#Menstrual#cycle#effects#on#caffeine#

elimination#in#the#human#female.#Eur%J%Clin%Pharmacol#43:#543-546,#1992.#

44.# Liguori#A,#Hughes#JR,#Grass#JA.#Absorption#and#subjective#effects#of#

caffeine#from#coffee,#cola#and#capsules.#Pharmacology%Biochemistry%and%

Behavior#58:#721-726,#1997.#

45.# Lohman#TG,#Roche#AF,#Martorell#R.#Anthropometric%standardization%

reference%manual.#Champaign,#IL:#Human#Kinetics#Books,#1988.#

46.# Lorino#AJ,#Lloyd#LK,#Crixell#SH,#Walker#JL.#The#effects#of#caffeine#on#

athletic#agility.#J%Strength%Cond%Res#20:#851-854,#2006.#

47.# Lorist#MM,#Snel#J,#Kok#A,#Mulder#G.#Influence#of#caffeine#on#selective#

attention#in#well-rested#and#fatigued#subjects.#Psychophysiology#31:#525-

534,#1994.#

48.# Machado#M,#Koch#AJ,#Willardson#J,#Santos#FC,#Curty#VM.#Caffeine#does#not#

augment#markers#of#muscle#damage#or#leukocytosis#following#resistance#

exercise.#Int%J%Sports%Phys%Perf#5:#18-26,#2010.#

49.# Mayhew#JL,#Ball#TE,#Arnold#MD,#Bowen#JC.#Relative#muscular#endurance#

performance#as#a#predictor#of#bench#press#strength#in#college#men#and#

women.#J%Strength%Cond%Res#6:#200-206,#1992.#

50.# Mayhew#JL,#Ware#JS,#Bemben#MG,#Wilt#B,#Ward#TE,#Farris#B,#Juraszek#J,#

Slovak#JP.#The#NFL-225#test#as#a#measure#of#bench#press#strength#in#

college#football#players.#J%Strength%COnd%Res#13:#130-134,#1999.#

51.# McArdle#WD,#Katch#FL,#Katch#VL,.#Exercise%physiology:%energy,%nutrition,%

and%human%performance.#Baltimore,#MD:#Lippincott#Williams#&#Wilkins,#

2001.#

52.# http://www.acsm.org/docs/current-comments/caffeineandexercise.pdf#

Accessed#03#May#2015.#

53.# Minton#DM,#ONeal#EK,#Torres-McGehee#TM.#Agreement#of#urine#specific#

gravity#measurements#between#manual#and#digital#refractometers.#J%

Athletic%Training#50:#59-64,#2015.#

54.# Nam#SW,#Choi#DJ,#Kim#SK,#Her#N,#Zoh#KD.#Adsorption#characteristics#of#

selected#hydrophilic#and#hydrophobic#micropollutants#in#water#using#

activated#carbon.#J%Hazardous%Materials#270:#144-152,#2014.#

55.# Nehlig#A.#Is#caffeine#a#cognitive#enhancer?#J%Alzheimers%Dis#20:#85-94,#

2010.#

56.# Noakes#TD.#Effect#of#exercise#on#serum#enzyme#activities#in#humans.#

Sports%Med#4:#245-267,#1987.#

57.# Norager#CB,#Jensen#MB,#Madsen#MR,#Laurberg#S.#Caffeine#improves#

endrance#in#75-yr-old#citizens:#a#randomized,#double-blind,#placebo-

controlled#crossover#study.#J%Appl%Physiol#99:#2302-2306,#2005.#

58.# O'Rourke#MP,#O'Brien#BJ,#Knez#WL,#Paton#CD.#Caffeine#has#a#small#effect#on#

5-km#running#performance#of#well-trained#and#recreational#runners.#J%Sci%

Med%Sport#11:#231-233,#2007.#

59.# Paton#CD,#Hopkins#WG,#Vollebreght#L.#Little#effect#of#caffeine#ingestion#on#

repeated#sprints#in#team-sport#athletes.#Med%Sci%Sports%Exerc#33:#822-825,#

2001.#

60.# Pesta#DH,#Angadi#SS,#Burtscher#M,#Roberts#CK.#The#effects#of#caffeine,#

nicotine,#ethanol,#and#tetrahydrocannabinol#on#exercise#performance.#

Nutrition%&%Metabolism#10,#2013.#

61.# Plaskett#CJ,#Cafarelli#E.#Caffeine#increases#endurance#and#attenuates#force#

sensation#during#submaximal#isometric#contractions.#J%Appl%Physiol#91:#

1535-1544,#2001.#

62.# Powers#SK,#Byrd#RJ,#Tulley#R,#Callender#T.#Effects#of#caffeine#ingestion#on#

metabolism#and#performance#during#graded#exercise.#Eur%J%Appl%Physiol#

50:#301-307,#1983.#

63.# Rall#TW.#Goodman%and%Gilman's%Pharmacological%Basis%of%Therapeutics.#

McGraw-Hill,#1993.#

64.# Ressig#CJ,#Strain#EC,#Griffiths#RR.#Caffeinated#energy#drinks#--#a#growing#

problem.#Drug%Alcohol%Depend#99,#2009.#

65.# Reynolds#JM,#Gordon#TJ,#Robergs#RA.#Prediction#of#one#repetition#

maximum#strength#from#multiple#repetition#maximum#testing#and#

anthropometry.#J%Strength%Cond%Res#20:#584-592,#2006.#

66.# Robertson#D,#Wade#D,#Workman#R,#Woosley#RL,#Oates#JA.#Tolerance#to#the#

humoral#and#hemodynamic#effects#of#caffeine#in#man.#J%Clin%Invest#67:#

1111-1117,#1981.#

67.# Rush#JW,#Spriet#LL.#Skeletal#muscle#glycogen#phosphorylase#a#kinetics:#

effects#of#adenine#nucleotides#and#caffeine.#J%Appl%Physiol#91:#2071-2078,#

2001.#

68.# Sayers#SP,#Harackieqicz#DV,#Harman#EA,#Frykman#PN,#Rosenstein#MT.#

Cross-validation#of#three#jump#power#equations.#Med%Sci%Sports%Exerc#31:#

572-577,#1999.#

69.# Smith#A.#Effects#of#caffeine#on#human#behavior.#Food%Chem%Toxicol#40:#

1243-1255,#2002.#

70.# Spriet#LL.#Caffeine#and#performance.#Int%J%Sports%Nutrition#5:#S84-99,#1995.#

71.# Statland#BE,#Demas#TJ.#Serum#caffeine#half-lives.#Healthy#subjects#vs.#

patients#having#alcoholic#hepatic#disease.#Am%J%Clin%Pathol#73:#390-393,#

1980.#

72.# Sylvén#C,#Jonzon#B,#Fredholm#BB,#Kaijser#L.#Adenosine#injection#into#the#

brachial#artery#produces#ischaemia#like#pain#or#discomfort#in#the#forearm.#

Cardiovasc%Res#22:#674-678,#1988.#

73.# Tallis#J,#Duncan#MJ,#James#RS.#What#can#isolated#skeletal#muscle#

experiments#tell#us#about#the#effects#of#caffeine#on#exercise#performance?#

British%Journal%of%Pharmacology#172:#3703-3713,#2015.#

74.# Wagner#DR,#Heyward#VH,#Gibson#AL.#Validation#of#air#displacement#

plethysmography#for#assessing#body#composition.#Med%Sci%Sports%Exerc#32:#

1339-1344,#2000.#

75.# Walker#GJ,#Finlay#O,#Griffiths#H,#Sylvester#J,#Williams#M,#Bishop#NC.#

Immunoendocrine#response#to#cycling#following#ingestion#of#caffeine#and#

carbohydrate.#Med%Sci%Sports%Exerc#39,#2007.#

76.# Wells#SG.#Caffeine:#implications#of#recent#research#for#clinical#practice.#Am%

J%Orthopsychiatry#54,#1984.#

77.# Williams#AD,#Cribb#PJ,#Cooke#MB,#Hayes#A.#The#effect#of#ephedra#and#

caffeine#on#maximal#strength#and#power#in#resistance-trained#athletes.#J%

Strength%Cond%Res#22:#464-470,#2008.#

78.# Woolf#K,#Bidwell#WK,#Carlson#AG.#Effect#of#caffeine#as#an#ergogenic#aid#

during#anaerobic#exercise#performance#in#caffeine#naïve#collegiate#football#

players.#J%Strength%Cond%Res#25:#1363-1369,#2009.#

79.#######World#Anti-Doping#Agency.#The#2015#monitoring#program.#wada-main-

prod.s3.amazonaws.com/resources/files/wada-2015-monitoring-

program-en.pdf.#Accessed#18#May#2016.#