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THE ACUTE EFFECTS OF ACAFFEINE-CONTAININGSUPPLEMENT ON BENCH PRESS STRENGTH AND TIME

TO RUNNING EXHAUSTIONTRAVIS W. BECK, TERRYJ. HOUSH, MOH H. MALEK, MICHELLE MIELKE, AND RUSSELL HENDRIX

Department of Nutrition and Health Sciences, Human Performance Laboratory, University of Nebraska-Lincoln, Lincoln,Nebraska

ABSTRACT

Beck, TW, Housh, TJ, Malek, MH, Mielke, M, and Hendrix, R.

The acute effects of a caffeine-containing supplement on bench

press strength and time to running exhaustion.J Strength Cond

Res 22(5): 16541658, 2008The purpose of the present study

was to examine the acute effects of a caffeine-containing supple-ment (SUPP) on one-repetition maximum (1-RM) bench press

strength and time to running exhaustion (TRE) at a velocity that

corresponded to 85% of the peak oxygen uptake ( _VO2peak).

The study used a double-blinded, placebo-controlled, crossover

design. Thirty-one men (mean 6 SD age = 23.0 6 2.6 years)

were randomly assigned to take either the SUPP or placebo

(PLAC) first. The SUPP contained 201 mg of caffeine, and the

PLAC was microcrystalline cellulose. All subjects were tested

for 1-RM bench press strength and TRE at 45 minutes after

taking either the SUPP or PLAC. After 1 week of rest, the

subjects returned to the laboratory and ingested the opposite

substance (SUPP or PLAC) from what was taken during theprevious visit. The 1-RM bench press and TRE tests were then

performed in the same manner as before. The results indicated

that the SUPP had no effect on 1-RM bench press strength or

TRE at 85% _VO2peak. It is possible that the acute effects of

caffeine are affected by differences in training status and/or the

relative intensity of the exercise task. Future studies should

examine these issues, in addition to testing the acute effects of

various caffeine doses on performance during maximal

strength, power, and aerobic activities. These findings do

not, however, support the use of caffeine as an ergogenic aid in

untrained to moderately trained individuals.

KEYWORDS caffeine, strength, endurance

INTRODUCTION

Caffeine has become a popular ergogenic aid among

recreational and competitive athletes. The pro-

posed benefits of caffeine include increased

secretion of catecholamines (epinephrine and

norepinephrine) (11), greater use of fats as an energy sourceand sparing of muscle glycogen (6), and increased motor unit

recruitment and firing rates (13). Most studies, however, have

tested caffeines effects on measures of endurance (e.g., time to

exhaustion at fixed power outputs or speeds during cycling or

running tasks) (6,9,10,14,17,18) or anaerobic performance (e.g.,

peak power and mean power output during Wingate

anaerobic tests, swimming velocity during 100-m swimming

sprints, or time required to complete a 2000-m rowing trial)

(2,4,5). Generally speaking, these investigations have reported

that caffeine improved performance during endurance-based

activities (6,10), but the results during anaerobic activities have

been less consistent (2,5). For example, we recently found that

a 201-mg dose of caffeine taken 45 minutes before exercise hadno effect on peak power or mean power output during two

consecutive Wingate anaerobic tests (separated by 7 minutes

of rest) in college-aged resistance-trained men (2). Collomp

et al. (5), however, report that a slightly larger dose of caffeine

(250 mg) ingested 1 hour before exercise resulted in

a significant increase in average swimming velocity for trained

swimmers during two 100-m swimming sprints separated by

20 minutes of rest. Although the discrepancies between the

results from these studies (2,5) could have been caused by the

use of slightly different caffeine doses, it is more likely that they

reflected differences in the types of activities that were

performed (i.e., cycling vs. swimming).

Because many recreationally trained athletes perform bothresistance- and endurance-based training, they may be inter-

ested in a sports supplement that could enhance performance

during both types of activities. Similarly, there are several

competitive sports that require athletes to demonstrate high

levels of muscular strength and power in addition to endur-

ance (e.g., wrestling, boxing, basketball, field hockey, tennis,

etc.). Thus, some competitive athletes may also be interested

in a sports supplement that enhances performance during

both aerobic and anaerobic activities. The mechanisms by

Address correspondence to Travis W. Beck, [email protected].

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which caffeine enhances performance during aerobic activ-ities have been examined in many studies, and mostinvestigations have suggested that caffeines ergogenic effects

on endurance are attributable, at least partially, to increaseduse of fats as an energysource and sparing of muscle glycogen(6,8,16). Very few investigations, however, have examined the

mechanism(s) by which caffeine could enhance performanceduring maximal strength tasks. Kalmar and Cafarelli (13)

recently have suggested that caffeines action as an adenosinereceptor antagonist could help to enhance motor unit

recruitment and/or firing rates, both of which wouldcontribute to increases in force production. However, this

hypothesis has only been tested for the leg extensors duringa unilateral isometric muscle action (13). Thus, there is verylittle information regarding caffeines effects on strength,

particularly for activities that are commonly performed byboth recreational and competitive athletes (e.g., bench

presses, power cleans, squats, leg extensions, etc.). Further-more, previous studies (9,10) have reported acute increases in

performance from caffeine doses that result in urinarycaffeine concentrations well below the legal limit of 12 mgof caffeine per milliliter of urine, set by the InternationalOlympic Committee. Thus, these findings (9,10) suggest that,

for some activities, caffeine may provide a competitive edgewithin the established limits set by regulating organizations.

Therefore, the purpose of the present study was to examinethe acute effects of a caffeine-containing supplement

(SUPP) on one-repetition maximum (1-RM) bench pressstrength and time to running exhaustion (TRE) at a velocitythat corresponded to 85% of the peak oxygen uptake

(_VO2peak).

METHODS

Experimental Approach to the Problem

This study used a randomized, double-blinded, placebo-

controlled, crossover design. During the first laboratory visit,the subjects performed an incremental test to exhaustion on

a treadmill to determine _VO2peak. After the _VO2peak test,the subjects were allowed to rest for 1 week. After the 1-weekrest period, the subjects returned to the laboratory and were

randomly assigned to ingest either the SUPP or the placebo(PLAC) first. Table 1 shows the ingredients for the SUPP.

The PLAC (microcrystalline cellulose) was designed by themanufacturer (General Nutrition Corporation, Pittsburgh,

Pa) such that each dose (two tablets = one dose) had thesame volume, taste, and color as the SUPP. After

randomization, the subjects ingested one dose of either theSUPP or the PLAC and sat quietly in the laboratory for45 minutes. The subjects were then tested for 1-RM bench

press strength. Approximately 15 minutes after the 1-RMbench press strength test, the subjects were tested for TRE ata velocity that corresponded to 85% of their _VO2peak. After

the TRE test, the subjects were allowed to rest for 1 week,during which they did not ingest either the SUPP or the

PLAC. After the 1-week rest period, the subjects returned tothe laboratory and took the opposite substance (SUPP orPLAC) from what they took during the second laboratory

visit. The subjects then performed the bench press 1-RM andTRE tests in the same manner as during the previous visit.

Subjects

Thirty-one men (mean 6 SD age = 23.0 6 2.6 years)volunteered to participate in the investigation. Most of the

TABLE1. The ingredients contained in one dose of the caffeine-containing supplement.

IngredientCaffeine-containing supplement: amount

per serving (mg)

Yerba Mate extract (Ilex paraguariensis) (8% caffeine = 40 mg) 500.0Guarana seed extract (Paullinia cupana) (36% caffeine = 152 mg) 422.0Black tea extract (Camellia sinensis) (9% caffeine = 9 mg) 100.0Ginger extract (Zingiber officinale) (5% gingerols) 500.0Schisandra chinensis fruitextract 100.0Dill weed extract (Anethum graveolens) 5.0Grape seed extract (Vitis vinifera) 1.0Vitamin C (as ascorbic acid) 120.0

Niacin 40.0Vitamin B6 (as pyridoxine hydrochloride) 2.0Pantothenic acid (as calcium D-pantothenate) 10.4Wild blueberry extract (Vaccininium angustifolium) 100.0Cinnamon 25.0Red pepper extract (capsaicin = 4 mg) 10.0Black pepper extract 5.0

Total caffeine content for one dose of the caffeine-containing supplement was approximately 201.0 mg. The placebo wasmicrocrystalline cellulose.

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subjects were untrained in both resistance and aerobicexercise, but some reported engaging in no more than4 hours of recreational activity per week. In addition, the

subjects did not report or exhibit (a) a history of medical orsurgical events that may significantly affect the studyoutcome, including cardiovascular disease, metabolic, renal,

hepatic, or musculoskeletal disorders, (b) use of anymedication that may significantly affect the study outcome,

(c) use of nutritional supplements (such as creatine, proteindrinks, amino acids, and vitamins) in the 6 weeks before the

start of the study, or (d) participation in another clinical trialor ingestion of another investigational product within 30 days

before screening/enrollment. The study was approved by theuniversity institutional review board for human subjects, andall subjects completed a health history questionnaire and

signed a written informed consent document before testing.

Determination of Peak Oxygen Uptake

Each subject performed an incremental test to exhaustion on

a motorized treadmill (Precor C962i, Woodinville, Wash) for thedetermination of _VO2peak. All subjects wore a nose clip and

breathed through a two-way valve (2700; Hans Rudolph,Kansas City, Mo). Expired gas samples were collected and

analyzed using a calibrated TrueMax 2400 metabolic cart(Parvo Medics, Sandy, Utah) with O2, CO2, and ventilatoryparameters expressed as 20-second averages. The metabolic

cart was calibrated before each test. Each subject was fitted witha Polar Heart Watch system (Polar Electro Inc., Lake Success,NY) to monitor heart rate throughout the test. After a 5-minute

warm-up at 4.83 kmh21 and 0% grade, the test began with thesubject walking at 6.44 kmh21 and 0% grade. The velocity was

increased 1.61 kmh21 every 2 minutes to 14.49 kmh21. At

14.49 kmh21

, the exercise intensity was increased by raising thetreadmill grade 2% every 2 minutes until voluntary exhaustion.

Peak oxygen uptake was defined as the highest value recordedduring the last 30 seconds of the test.

Bench Press One-Repetition Maximum Strength Test

The bench press 1-RM strength test was performed ona standard free-weight bench (Body Power, Williamsburg, Va)

with an Olympic bar. After receiving a lift-off from a spotter,the subject lowered the bar to his chest, paused briefly, and

then pressed the bar to full extension of the forearms. The1-RM was determined by applying progressively heavier loads

until the subject could not complete a repetition through thefull range of motion (full extension of the forearms). Additionaltrials were performed with lighter loads until the 1-RM was

determined within 2.27 kg, and this was usually achievedwithin five trials. Two minutes of rest were allowed between all

trials (12). The intraclass correlation coefficient for bench press1-RM strength for our laboratory is R = 0.99, with nosignificant mean difference between test and retest values.

Time to Running Exhaustion Test

One week after the _VO2peak test, each subject performed

a constant-velocity treadmill run test to determine TRE.

After a 5-minute warm-up at 4.83 kmh21 and 0% grade, thesubject began running at a velocity that corresponded to 85%of the velocity at _VO2peak as determined during the_VO2peak test. Each subject was instructed to run until

voluntary exhaustion, and strong verbal encouragement wasprovided. Billat et al. (3) report that during continuous, high-

intensity treadmill running, there was no significant meandifference between TRE values from two tests separated

by 1 week, and the two measurements were correlated atr= 0.864.

Statistical Analyses

Bench press 1-RM strength and TRE values were comparedbetween the SUPP vs. PLAC using two separate paired-

samples t-tests. An alpha of p # 0.05 was consideredstatistically significant for all comparisons. An a priori poweranalysis indicated that for a repeated-measures design,a sample size of 31 subjects resulted in statistical power

values of 0.90 or greater for both of the dependent variables.

RESULTS

The mean 6 SEM bench press 1-RM strength values for theSUPP and PLAC were 77.3 6 3.6 and 76.9 6 3.6 kg,

respectively (Figure 1). Figure 1 shows the mean 6 SEMTRE values for the SUPP (856.1 6 63.5 seconds) and PLAC

(850.5 6 59.7 seconds). There were no significant meandifferences for the SUPP vs. PLAC for bench press 1-RMstrength or TRE values.

DISCUSSION

The results of this investigation show that the 201-mg dose ofcaffeine in the SUPP had no effect on 1-RM bench press

strength. These data are not consistent with those froma recent study from our laboratory (2), as well as withresearch that has examined the acute effects of caffeine on

unilateral isometric leg extension strength (13). For example,in our previous investigation (2), we found that a 201-mg

dose of caffeine ingested 45 minutes before exercise resultedin a significant increase (2.1 kg = 2.1%) in 1-RM bench press

strength. Although the present study used the same caffeinedose and bench press 1-RM testing procedures, the subjectsin our previous investigation (2) were experienced in weight

training (regularly participating in at least four resistancetraining sessions per week), whereas those in the presentstudy were mostly untrained. Thus, it is possible that the

acute effects of caffeine on strength are influenced bydifferences in training status. This hypothesis is consistent

with the suggestion that caffeine may have a greaterergogenic effect in trained vs. untrained individuals (5,8,9).

There are very few data, however, regarding the mecha-

nisms by which caffeine could affect performance duringmaximal strength/power activities. Kalmar and Cafarelli (13)

used the twitch interpolation technique to examine theacute effects of caffeine (6 mgkg21 body weight ingested

1 hour before exercise) on strength and maximal voluntary


Effects of Caffeine on Strength and Endurance


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activation of the vastus lateralis during a unilateral isometricmaximum voluntary contraction of the leg extensors. The

authors (13) report that the caffeine resulted in significantincreases in both isometric leg extension strength (approx-imately 6% increase) and maximal voluntary activation for

the vastus lateralis muscle (approximately 3% increase). Theyhypothesize (13) that the caffeine may have acted supra-spinally as an adenosine receptor antagonist. Specifically,

binding of adenosine to its receptor in the central nervoussystem (CNS) usually inhibits neurotransmitter release and

decreases neuronal firing rates, both of which can result inreduced muscle activation and force production (13).

However, binding of caffeine with adenosine receptors inthe CNS may allow for greater motor unit recruitmentand/or firing rates (from competitive inhibition of adeno-

sine), both of which could increase maximal voluntaryactivation and force production (13). An alternative hypoth-

esis is that caffeine acts peripherally by increasing thepermeability of the sarcoplasmic reticulum to calcium (1).Theoretically, this could result in higher calcium concen-

trations in the sarcoplasm during muscle contraction, therebyincreasing the amount of force produced during tetanus (i.e.,

tetanic tension) (1). It has beensuggested, however, that thecaffeine doses necessary to

have an effect on calciumpermeability at the sarcoplas-mic reticulum may be toxic to

humans (13). Regardless of theexact mechanism, the results

from the present study do notprovide support for the use of

caffeine before measuring 1-RM bench press strength. Be-

cause there are very few studiesthat have examined the acuteeffects of caffeine on muscular

strength, more research needsto be done to investigate the

influence of different doses ofcaffeine on strength during

various types of activities.These studies should also usetrained and untrained individ-uals to determine whether the

acute effects of caffeine areinfluenced by differences in

training status.The results from this inves-

tigation also show that theSUPP had no effect on TRE at85% _VO2peak. Many studies

have found that caffeineimproves endurance during ac-

tivities that last 3060 minutes(6,11,14,16,17,18). The most common hypothesis used toexplain this phenomenon is that caffeine supplementation

increases the use of fatty acids as an energy substrate, therebysparing muscle glycogen (6,8,18). Although there are data tosupport this suggestion (6,17), there is also research indicating

that a glycogen sparing effect may not be the onlymechanism responsible for caffeine-induced increases in

endurance (11, p. 1837). For example, Greer et al. (11)examined the acute effects of caffeine (6 mgkg21 body weight

ingested 90 minutes before exercise) on muscle glycogencontent (assessed with muscle biopsies) during a 45-minute

cycle ergometer workbout at 6570% _VO2peak. The authors

(11) report that the decreases in muscle glycogen throughoutthe workbout were similar when the subjects ingested caffeine

vs. a dextrose placebo. However, blood glycerol levels afteringesting caffeine were significantly higher at all time points

during the 45-minute workbout when compared with thoseafter taking the placebo (11). Thus, it was suggested thatalthough caffeine supplementation may promote increased

use of fatty acids as an energy substrate during exercise, it maynot necessarily decrease the rate of muscle glycogen lossduring exercise (11).

Figure 1.The top graph shows the results of the bench press one-repetition maximum (1-RM) strength test for the

supplement (SUPP) and placebo (PLAC). The bottom graph shows the results of the time to running exhaustion

(TRE) test for the SUPP and PLAC. The values shown in both graphs are means 6 SEM. There were no significant

(p . 0.05) mean differences for the SUPP vs. PLAC for bench press 1-RM strength or TRE values.

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It is important to note that muscle glycogen stores may nothave been the primary factor determining performanceduring the TRE task in the present study. The mean TRE

values for the SUPP and PLAC were 856.1 seconds(14.3 minutes) and 850.5 seconds (14.2 minutes), respectively(Figure 1). Although muscle glycogen and blood lactate were

not measured in this investigation, it is possible that TRE at85% _VO2peak was influenced more by the accumulation of

metabolites (e.g., lactate, inorganic phosphate, ammonia) thandepletion of energy substrates (e.g., glycogen). This hypothesis

is supported by the results from studies that have examined theacute effects of caffeine on performance during exercise tasks

that elicit fatigue within 1020 minutes (7,15). For example,Powers et al. (15) report that during an incremental cycleergometer test (beginning workload of 30 W, with 30-W

increases every 3 minutes until exhaustion), caffeine supple-mentation (5 mgkg21 body weight ingested 1 hour beforeexercise) had no effect on total exercise time to exhaustion or

the rate of blood lactate accumulation. Dodd et al. (7) used

a similar exercise protocol (incremental cycle ergometry witha beginning workload of 50 W, with 30-W increases every2 minutes until exhaustion) and report that two differentcaffeine doses (3 or 5 mgkg21 body weight) resulted in

significant increases in plasma free fatty acid concentration buthad no effect on the lactate threshold or total exercise time to

exhaustion. Thus, our findings for TRE are similar to those ofPowers et al. (15) and Dodd et al. (7) and suggest that caffeine

may not affect performance during high-intensity activitiesdesigned to elicit fatigue within 1020 minutes. Future studiesshould test this hypothesis with different caffeine doses during

both running and cycling activities.In summary, the results from this study show that the

201-mg dose of caffeine in the SUPP had no effect on 1-RMbench press strength or TRE at 85% _VO2peak. It is possiblethat the acute effects of the SUPP were influenced by

differences in training status and/or the relative intensity ofthe exercise task. Future studies should examine these issuesin addition to testing the acute effects of various caffeine

doses on performance during maximal strength/poweractivities and other high-intensity, short-duration activities.

PRACTICAL APPLICATIONS

The results from this study indicate that ingestion ofa caffeine-containing supplement had no effect on upper-

body strength or endurance running performance in

untrained to moderately trained men. Thus, these findingsdo not support theuse of caffeineas an ergogenic aid forthese

individuals. The results from previous studies suggest that theacute effects of caffeine on upper-body strength (2) and sprint

swimming performance (5) may be greater for trained vs.untrained individuals. Thus, future studies should examinethe influence of differences in training status on the acute

effects of caffeine, in addition to testing various dosagesduring different types of activities.

ACKNOWLEDGEMENTS

This study was funded by a research grant from GeneralNutrition Corporation.

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