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Journal of Strength and Conditioning Research, 2004, 18(3), 463–465 ᭧ 2004 National Strength & Conditioning Association PHYSIOLOGIC EFFECTS OF CAFFEINE ON CROSS-
COUNTRY RUNNERS
LARRY J. BIRNBAUM AND JACOB D. HERBST
Department of Exercise Physiology, College of St. Scholastica, Duluth, Minnesota 55811. ABSTRACT. Birnbaum, L.J., and J.D. Herbst. Physiologic effects
capsules), and nutritional and genetic differences among of caffeine on cross-country runners. J. Strength Cond. Res. the subjects. Some studies controlled for previous caffeine 18(3):463–465. 2004.—This study determined the physiological use by asking subjects to abstain for a period of time—12 effects of caffeine on cross-country runners during submaximal hours (2), 6 hours (8), 2 weeks (17), or 15 hours (19)—but exercise. Ten college-age subjects (5 women; 5 men) volunteered the effectiveness is questionable in light of how ubiqui- to participate in this study. After completing a V subject completed 2 30-minute runs at 70% V tous caffeine is in the American diet. It is unlikely that treadmill, 1 after ingesting caffeine and the other after ingesting the physiologic adaptations to long-term caffeine use are a placebo. A caffeine dosage of 7 mg·kgϪ1 of body weight was reversed by abstaining for a few hours, although Powers administered. The same dosage of vitamin C was used as a pla- et al. (17) asked subjects to abstain for 2 weeks. It is also cebo. The order of treatments was randomly assigned, and the difficult to control the diet of voluntary subjects. The in- trials followed a double-blind format. The physiological data gestion of caffeine as coffee versus as powder in gelatin were analyzed using a repeated measures analysis of variance capsules may contribute to equivocal results. Graham (SPSS). Tidal volume (T ), alveolar ventilation (V ), and rating and Spriet (10) suggest that components in coffee may of perceived exertion (RPE) were significantly different (p Ͻ negate the ergogenic actions of caffeine.
0.05) between treatment and control groups. The results suggest Given the discrepant results of past caffeine studies, that the ingestion of caffeine at 7 mg·kgϪ1 of body weight priorto submaximal running might provide a modest ergogenic effect the present study sought to determine if caffeine affected via improved respiratory efficiency and a psychological lift.
any 1 of several physiological parameters during sub-maximal exercise. Specifically, the responses measured or KEY WORDS. ergogenic aid, oxygen consumption, RPE, tidal vol- calculated included relative oxygen consumption (V heart rate (HR), systolic and diastolic blood pressure(SBP, DBP), double product (DP), pulmonary ventilation (V ), frequency of breaths (F ), tidal volume (T ), alveolar NTRODUCTION
ventilation (V ), and rating of perceived exertion (RPE).
affeine has been studied as an ergogenic aid by Cnumerousinvestigators.Asignificantergogenic METHODS
effect for caffeine has been reported as either an Experimental Approach to the Problem
an improvement in performance times (2, 6, 18). Other Ten college students, all of whom were cross-country run- studies have reported no significant effect for caffeine on ners, volunteered to participate in this study. Their de- mographic data are provided in Table 1. As cross-country ical variables (4, 19, 20). These divergent results may be runners, they were in postseason training, which involved partly explained by differences in caffeine dosage, exer- moderate-intensity training. All subjects were instructed cise protocols, or unknown factors. For example, in Mc- to refrain from any exercise 24 hours prior to testing.
Naughton’s study (15), 15 mg·kgϪ1 of caffeine produced a Both men and women were included, as no gender differ- significant improvement in performance time, but a 10- ences in caffeine sensitivity were reported by investiga- mg·kgϪ1 dose had no effect. This result would appear to tors who included both men and women in their studies be a function of the dosage. However, some studies that (4, 6, 7), and all subjects were tested at 70% V used a relatively low dosage of caffeine (approximately 5 negate differences in absolute oxygen consumption. Each mg·kgϪ1) did not observe any significant effects (4, 11), subject signed an informed consent and completed a Par- while others that used the same or very similar dosage Q health screening questionnaire. The study was ap- reported significant changes in performance time and/or proved by the College’s Institutional Review Board.
Exercise protocols have also varied in the published studies. Some studies had subjects run or cycle to ex- after ingesting caffeine and the other after ingesting a haustion, but the exercise intensity varied (3, 4, 6, 15, 17, ˙ O max test and each 30-minute trial were 18). Other investigators exercised subjects for a set period spaced 1 week apart. One week was deemed sufficient to of time at a fixed intensity (7, 8, 11, 18, 19, 20). The re- fully recover from exercise testing and to eliminate caf- sults of these studies were mixed, and a clear pattern feine from the body. According to Wadler and Hainline regarding exercise protocols and significant effects of caf- (22), caffeine has a half-life of 2–10 hours. A prepared caffeine dosage of 7 mg·kgϪ1 of body weight was admin- Other factors that may contribute to the varied results istered as a powder in gelatin capsules. This dosage was include previous caffeine use by subjects, the manner in selected since smaller dosages did not achieve an effect which caffeine was administered (e.g., coffee vs. caffeine in several studies (3, 4, 17, 19), and higher doses might TABLE 1. Subject characteristics (mean Ϯ SD).*
sphygmomanometer on the left arm. The treadmill was a A repeated measures analysis of variance (SPSS) was used to analyze the data. Results were considered statis- tically significant at p Յ 0.05. Exercise values were de- rived by averaging the 10th-, 20th-, and 30th-minute val- produce adverse symptoms in caffeine-naive subjects. Vi- No significant differences were observed in the cardio- tamin C served as the placebo and was also administered vascular responses or respiratory responses with the ex- as a powder in the same gelatin capsules and in the same ception of T and V (Table 2). Tidal volume (p ϭ 0.003) dosage. Vitamin C was selected as a placebo because it and V (p ϭ 0.039) increased significantly in the caffeine has no known exercise benefits (14, 22); it is also harm- group. A statistically significant decrease in RPE (p ϭ less in low to moderate doses and cannot be distinguished 0.037) was also found in the caffeine group.
from caffeine in powder form. The vitamin C and caffeinecapsules were indistinguishable. Neither the subjects nor DISCUSSION
the assistants collecting the data knew which capsulescontained the placebo or the caffeine. The primary inves- The results of this study indicate that caffeine does not tigator randomly selected which subjects received caffeine alter physiological parameters, with the exception of T , or vitamin C on their first trial by flipping a coin (heads V , and RPE, during submaximal exercise (70% V ϭ caffeine capsules; tails ϭ vitamin C capsules). The 30 minutes duration). Consequently, it is unlikely that treatment and control were switched for the second trial.
caffeine provides an improvement in energy expenditure Subjects were asked to abstain from caffeine for 4 days prior to testing to decrease the effect of caffeine tolerance.
sponses were unchanged. These results agree with sev- Only 1 subject admitted to being a regular caffeine user.
eral other studies. In particular, Toner et al. (21) and In a study by Fisher et al. (8), when habitual caffeine Gastin et al. (9) did not produce statistically significant cantly after ingesting 5 mg·kgϪ1 of caffeine. A list of com- feine did not produce significant changes in V mon beverages and foods that contain caffeine was given marathoners who ran for 45 minutes at 75% of their to each subject. Subjects were also asked to fast for 3 ˙ O max but did significantly decrease RPE (5). Bond et hours before arriving at the test site. On arrival, each al. (3) reported that caffeine did not alter V subject was given the caffeine or placebo with approxi- during conditions ranging from rest to maximum exer- mately 12 oz of water and then tested 1 hour later since cise. Tarnopolsky et al. (19) also failed to find significant caffeine levels peak 60 minutes after ingestion (22). Ini- ˙ O , HR, or RPE in varsity male runners who tially, resting data were collected, which included SBP, ran on a treadmill for 90 minutes at 70% V et al. (20) employed 60 minutes of treadmill running at collected every 10 minutes during exercise along with 60% of HR max and reported no significant changes in RPE using the Borg scale. Calculated data included DP, Conversely, Fisher et al. (8) reported that, after ab- The Medical Graphics Cardio O metabolic analyzer staining from caffeine for 4 days, 5 mg·kgϪ1 of caffeine produced a significant increase in submaximal V lyzer was calibrated with standard gases (21% O /0% CO max) in subjects habituated to caffeine. Engels et al.
and 12% O /5% CO ) prior to testing each subject. Both a (7) also reported a significant increase in V 3-lead ECG and a Polar heart rate monitor were used to measure HR. Blood pressure was determined by the same responses were also increased, but HR was not changed.
investigator for all subjects using a stethoscope and TABLE 2. Physiologic responses during moderate exercise.†
* p Ͻ 0.05.
† SD ϭ standard deviation; HR ϭ heart rate; SBP ϭ systolic blood pressure; DBP ϭ diastolic blood pressure; DP ϭ double product; V ϭ pulmonary ventilation; F ϭ frequency of breaths; T ϭ tidal volume; V ϭ alveolar ventilation.
PHYSIOLOGIC EFFECTS OF CAFFEINE ON CROSS-COUNTRY RUNNERS 465 ercise is often viewed as a decrease in running economy cardiorespiratory endurance in men and women. Res. Q. Exerc. (1). The increase in BP may be a function of caffeine’s influence on peripheral resistance (16).
CASAL, D.C., AND A.S. LEON. Failure of caffeine to affect sub- An explanation for these discrepant results is not strate utilization during prolonged running. Med. Sci. SportsExerc. 17:174–179. 1985.
readily apparent. The same caffeine dosage has produced COSTILL, D.L., G.P. DALKSY, AND W.J. FINK. Effects of caffeine conflicting results (3, 7, 8, 17), as has similar exercise ingestion on metabolism and exercise performance. Med. Sci. protocols (4, 7, 8, 20). The manner in which caffeine is administered (coffee vs. capsules) does not appear to offer ENGELS, H.J., J.C. WIRTH, S. CELIK, AND J.L. DORSEY. Influ- an explanation either. However, this study did find a sig- ence of caffeine on metabolic and cardiovascular functions dur- nificant increase in T (11.5%) and V (7.4%) during sub- ing sustained light intensity cycling and at rest. Int. J. Sport maximal exercise. This is most likely due to caffeine’s ability to produce bronchodilation (12, 22). Although the FISHER, S.M., R.G. MCMURRAY, M. BERRY, M.H. MAR, AND mechanism by which it changes airway tone is unclear W.A. FORSYTHE. Influence of caffeine on exercise performance (13), caffeine may also help individuals who suffer from in habitual caffeine users. Int. J. Sports Med. 7:276–280. 1986.
GASTIN, P.B., J.E. MISNER, R. A. BOILEAU, AND M.H. SLAUGH- exercise-induced asthma. By increasing T and V , the TER. Failure of caffeine to enhance exercise performance in in- efficiency of the respiratory apparatus is improved in that cremental treadmill running. Aust. J. Sci. Med. Sport 22:23– the subjects ventilated essentially the same minute vol- ume (64 vs. 61 L·minϪ1; p ϭ 0.104) with fewer breaths.
GRAHAM, T.E., AND L.L. SPRIET. Caffeine and exercise perfor- The decrease in ventilatory effort is further supported by mance. Sports Science Exchange (#60). 9(1):1–10. 1996. (http:// the significant increase in V . Both responses are directly www.gssiweb.com/reflib/refs/33/d000000020000006e.cfm?pidϭ related to the subjects’ decrease in RPE. As ventilatory efficiency improves, less exertion is required for respira- KAMINSKY, L.A., C.A. MARTIN, AND M.H. WHALEY. Caffeine tion. Thus, the subjects’ perception of effort was de- consumption habits do not influence the exercise blood pres-sure following caffeine ingestion. J. Sports Med. Phys. Fitness creased during the 30 minutes of submaximal exercise.
This finding is in agreement with Casal and Leon (5), who KAPLAN, L.A., AND A.J. PESCE. Clinical Chemistry: Theory, also found a caffeine-related decrease in perceived exer- Analysis and Correlation (3rd ed.). St. Louis, MO: Mosby-Year- LEONARD, T.K., R.R. WATSON, AND M.E. MOHS. The effects of PRACTICAL APPLICATIONS
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Given the increased T and V observed in this study and MCARDLE, W.D., F.I. KATCH, AND V.L. KATCH. Sports and Ex- the positive effect on respiratory effort, it is reasonable to ercise Nutrition. Philadelphia: Lippincott Williams & Wilkins, conclude that caffeine had a small but significant effect on pulmonary function during submaximal exercise. The MCNAUGHTON, L.R. The influence of caffeine ingestion on in- increase in V , in particular, indicates that the inspired cremental treadmill running. Brit. J. Sports Med. 20:109–112.
air reaching the alveoli and participating in gas exchange helped to ensure consistency in arterial blood gases, PINCOMB, G.A., W.R. LOVALLO, R.B. PASSEY, T.L. WHITSETT, which would otherwise compromise the respiratory re- S.M. SILVERSTEIN, AND M.F. WILSON. Effects of caffeine on vas- cular resistance, cardiac output, and myocardial contractility It might be argued that the decrease in RPE, while in young men. Am. J. Cardiol. 56:119–124. 1985.
statistically significant, may not be of practical signifi- OWERS, S.K., R.J. BYRD, R. TULLEY, AND T. CALLENDER. Ef- fects of caffeine ingestion on metabolism and performance dur- cance since RPE is measured in whole numbers on the ing graded exercise. Eur. J. Appl. Physiol. 50:301–307. 1983.
Borg scale. The mean RPE scores of 10.8 for the caffeine SASAKI, H., J. MAEDA, S. USUI, AND T. ISHIKO. Effect of sucrose group and 11.2 for the placebo group would both be 11 and caffeine ingestion on performance of prolonged strenuous when rounded to a whole number. Still the raw data were running. Int. J. Sports Med. 8:261–265. 1987.
in whole numbers, and the statistical analysis produced TARNOPOLSKY, M.A., S.A. ATKINSON, J.D. MCDOUGALL, D.B.
a finding of significance indicating that the subjects did SALE, AND J.R. SUTTON. Physiological responses to caffeine indeed perceive the effort to be less after ingestion of caf- during endurance running in habitual caffeine users. Med. Sci. feine. If a subject feels that less effort is being exerted, Sports Exerc. 21:418–424. 1989.
then that subject may be able to perform at a higher in- ITLOW, L.W., J.H. ISHEE, AND C.E. RIGGS. Failure of caffeine to affect metabolism during 60 min submaximal exercise. J. tensity and/or for a longer duration.
TONER, M.M., D.T. KIRKENDALL, D.J. DELIO, J.M. CHASE, P.A.
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The authors thank Dr. Tommy Boone, chair of the Exercise BOND, V. R. ADAMS, B. BALKISSOON, J. MCRAE, E. KNIGHT, S.
Physiology Department, for his assistance throughout this ROBBINS, AND M. BANKS. Effects of caffeine on cardiorespira- study. His expertise was invaluable.
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Address correspondence to Dr. Larry J. Birnbaum, BUTTS, N.K., AND D. CROWELL. Effect of caffeine ingestion on

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