Effects of Caffeine Ingestion on Exercise-Induced Changes During High-Intensity, Intermittent Exercise

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1 International Journal of Sport Nutrition, 1995, 5, O 1995 Human Kinetics Publishers, Inc. Effects of Caffeine Ingestion on Exercise-Induced Changes During High-Intensity, Intermittent Exercise Isaiah Trice and Emily M. Haymes In this study a double-blind design was used to determine the effect of caffeine on time to exhaustion and on associated metabolic and circulatory measures. Eight male subjects ingested either caffeine (5 mgkg body weight) or a placebo 1 hr prior to exercise at 85-90% of maximum workload. Subjects were encouraged to complete three 30-min intermittent cycling periods at 70 rpm with 5 min rest between each. The exercise was terminated when the subject failed to complete three 30-min periods or failed to maintain 70 rpm for at least 15 s consecutively. Serum free fatty acids, glycerol, blood glucose, lactate, perceived exertion, heart rate, and 0, cost were measured. The time to exhaustion was significantly longer during the caffeine trial than during the placebo trial. Serum free fatty acid levels were significantly different between trials. The decline in blood glucose levels was significantly less during the caffeine trial than during the placebo trial. There were no significant differences between trials for the other measures. It was concluded that caffeine increases time to exhaustion when trained subjects cycled intermittently at high levels of intensity. Key Words: exhaustion, free fatty acids, glucose, glycerol, oxygen cost caffeine has been reported to be an important ergogenic supplement to exercise. Some investigators have reported that it significantly increases performance time during prolonged continuous exercise (7,10,15). Although its effects on continuous exercise have been well documented, researchers such as Casal and Leon (3, Perkins and Williams (21), and Powers, Byrd, Tulley, and Callender (22) have questioned caffeine's effect on other kinds of exercise. Because other investigators have theorized, without documentation, that caffeine increases time to exhaustion during intermittent exercise (13,14,23), we decided to explore this relationship by testing the hypothesis that time to exhaustion during intermittent exercise would be significantly greater with a caffeine rather than a placebo treatment. I. Trice is with the Jean Meyer USDA Human Nutrition Research Center on Aging, Tufts University, 711 Washington St., Boston, MA E.M. Haymes is with the Department of Nutrition, Food, and Movement Sciences, Florida State University, Tallahassee, FL

2 38 / Trice and Hayrnes For purposes of the study, exhaustion was defined as the point at which the subject could not maintain 70 rpm for 15 s consecutively during the intermittent protocol. The subjects were encouraged to complete three 30-min exercise periods during which they pedaled 70 rpm for at least 15 s. There were 5 min of rest between each 30-min exercise period. Eight members of the Florida State University Rugby Club were tested on a cycle ergometer, using an intermittent protocol of alternating 1-min exercise and rest intervals. The purpose of this study was to determine if significant differences existed in time to exhaustion and levels of serum free fatty acids (FFA), serum glycerol, blood glucose, and blood lactate, as well as perceived exertion and oxygen cost when subjects were treated with 5 mgtkg body weight (BW) of caffeine or a placebo. Subjects Methods Eight trained male volunteers, ages 21-32, were recruited from the Florida State University Rugby Club. The physical characteristics of these subjects are described in Table 1. It was determined that the subjects were not regular caffeine users because of their verbal responses to a list of products containing caffeine. Prior to testing, medical clearance and informed written consent were obtained and the study was approved by the Institutional Review Board (IRB), which oversees the appropriate use of human subjects in experimental studies at Florida State University. Procedures Body density and percent body fat were estimated from the Jackson and Pollock (16) and Brozek, Grande, Anderson, and Keys (4) equations, respectively. V02. max was determined by using a continuous cycle ergometer test during which the intensity was increased by 30 W every 2 min (19). The intermittent exercise protocol consisted of 30 min of alternating I-min cycling and rest intervals. Subjects were encouraged to complete three 30-min cycling periods at 70 rpm with 5 min of rest between each period. They remained seated on the cycle ergometer during the rest phase. The first 30-min period began 1 hr after ingesting the coffee solution and continued until the subject completed three 30-min periods or failed to maintain 70 rpm for 15 s consecutively. The subjects pedaled 70 rpm at 85-90% of the maximum workload achieved during the preliminary Table 1 Description of Subjects (N = 8) Age Weight Body fat V0,max RHR (years) (kg) (%I (ml.kg.~w) (bpm) Mean SD

3 Caffeine Ingestion / 39 continuous cycle test. A Monarck cycle ergometer, Model 868, was used for all testing and exercise sessions. The caffeine and placebo treatments were randomly assigned at 7-day intervals by a double-blind, counterbalanced design. The placebo consisted of 10 oz warm water, 7 g decaffeinated coffee (Sanka), and 1 g sweetener (Equal). The caffeine treatment consisted of 10 oz warm water, 5 g decaffeinated coffee (Sanka), 1 g sweetener (Equal), and 5 mgtkg BW anhydrous caffeine powder (Pfizer, Inc.). Preliminary taste tests from our lab revealed that caffeine-naive subjects were unable to distinguish placebo and caffeine solutions when an additional 2 g decaffeinated coffee was added to the placebo and the temperature of both solutions was cooled before ingestion. Therefore, in order to disguise the differences in taste between the caffeine and placebo solutions, the placebo solution contained 2 g more of decaffeinated coffee than did the caffeine solution, and both caffeine and placebo solutions were cooled so that they could be swallowed rapidly. Experimental and Testing Protocols As soon as subjects reported to the laboratory, their body mass was measured and recorded to determine the caffeine dose. Two 7-ml Venus blood samples were drawn without stasis from the antecubital fossa 1 hr after subjects ingested the caffeine or placebo solution. Postexercise blood samples were taken immediately after exercise and analyzed using the YSI 200 Stat glucose~lactate analyzer. The remaining blood was allowed to clot, and serum was removed and stored at -10 "C until duplicate 200-p1 samples were analyzed for serum FFAs (Wako NEFA, Wako Chemicals, Dallas, TX) and serum glycerol (Stat-PackTM Behring Diagnostic, Inc.). Heart rate, ventilation, and pulmonary gas exchange were measured before the first interval and each minute between Minutes 6-10, 16-20, and of each exercise interval. These data were averaged to obtain the measures for each respective interval. Heart rate was monitored by the ExersentryTM chest-worn monitor. Ventilation and pulmonary gas exchange were measured using a Vacumed Spirometer, Applied Electrochemistry S-3A Oxygen Analyzer, and Ametek Carbon Dioxide Analyzer, Model CD-3A, interfaced with the REP 200 Data Acquisition System. Gas analyzers were calibrated using 15.64% O2 and 4.25% CO,. The volume of oxygen consumed was measured during Minutes 6-10, 16-20, and of each exercise interval and averaged to determine net oxygen cost (exercise V02 + recovery V02 - resting VO,) (8). Perceived exertion (RPE) was recorded at Minutes 9, 19, and 29 of each 30-min exerciselrest interval and averaged to determine the RPE for each 30-min interval (3). Testing took place after 12 hr of abstinence from food and 24 hr of abstinence from caffeine products. Each test protocol consisted of a caffeine or a placebo treatment at 0 min, plus a 60-min rest period followed by three 30-min exercise periods of alternating 1-min cycling and rest intervals. Subjects were encouraged to complete three 30-min periods of pedaling 70 rpm with 5 min of rest between each period. The exercise was terminated when the subject failed to complete three 30-min periods or failed to maintain 70 rpm for at least 15 s consecutively.

4 40 / Trice and Hayrnes Statistical Analysis Data were analyzed using paired t tests for time to exhaustion and a two-factor ANOVA repeated measures design for all other data. The Neuman-Keuls procedure was used to follow up all significant interactions. The.05 level of probability was accepted as significant. Data are presented as means S E. Results Time to exhaustion significantly increased by min after the caffeine treatment (77.5 f 5.26 min for the caffeine and for the placebo). The time range for time to exhaustion was min for caffeine treatment and min for the placebo treatment. The 50-min time was established by 1 subject who completed only 50 min for both caffeine and placebo treatments. There were no differences in net oxygen cost between the caffeine and placebo treatments (3.45 L f 0.30 L vs L L). However, there was a significant exercise-caffeine interaction (Table 2) for net oxygen cost. Its net cost increased significantly during the caffeine treatment from the first to the second exercise interval. Serum FFA concentration was significantly greater for the caffeine treatment ( mmol/l) than for the placebo (0.88 f mmol/l). Postexercise FFA levels increased significantly during the caffeine trial compared to resting FFA levels (Pre mmol/l; Post 1.58 f 0.12 mmol/l). Means for the two treatments are presented in Table 3. The main effect of caffeine on serum glycerol was not significant (p =.lo) but there was a significant exercise1 serum glycerol effect (Pre 0.98 f mg/dl; Post 2.78 f mg/dl). Means and SE for glycerol are also presented in Table 3. Although there was no main effect of treatment on blood glucose, there was a significant exerciselcaffeine interaction. Mean blood glucose decreased significantly during the placebo treatment ( vs f 4.2 mmol/l) (Table 3). Lactate increased significantly during exercise in both treatments (Pre 1.07 f 0.43 mmol/l; Post mmol/l), but there was no significant caffeinefiactate effect (Table 3). RPE increased significantly from the first to the second exercise bout (13.2 and 16.9, Table 2 Ventilation and Pulmonary Values for the First and Second Exercise Intervals With and Without Caffeine Placebo Caffeine Interval 1 Interval 2 Interval 1 Interval 2 M SE M SE M SE M SE p value 0,cost *.04 RPE HR voz "Significant differences between the first and second intervals with caffeine treatment.

5 Caffeine Ingestion / 41 Table 3 Pre and Post Serum and Blood Values During Exercise and Recovery With and Without Caffeine Placebo Caffeine Pre Post Pre Post p value M SE M SE M SE M SE FFA (mmolb) *.02 Glycerol (rngldl) Glucose (rnmoll) *.02 Lactate (mrnolb) *Significant differences before and after exercise in caffeine treatment. respectively). The main effect of caffeine on perceived exertion was not significant (p =.07) between caffeine ( ) and placebo ( ) treatment means (Table 2). Mean heart rates were not significantly different between caffeine ( bpm) and placebo ( bpm). Heart rates also increased significantly from the first ( ) to second ( ) exercise interval (Table 2). Discussion The intermittent exercise protocol of alternating 1-min exercise and rest intervals on a cycle ergometer used in this study was based on data reported by Astrand et al. (1,2) and Keul(17) as well as on preliminary tests performed in the Florida State University Exercise Physiology Laboratory. Our tests showed that trained subjects could cycle intermittently at rpm for up to 1 hr at 85-90% of the load achieved at V02max during the preliminary continuous cycling test. These tests were structured because data indicated that exercise can be performed intermittently at near-maximal intensity with only submaximal energy output (12) because the additional 0, required is provided during the recovery phase. Gollnick et al. (12) had shown previously that cycle exercise requiring an energy production of 150% of V02max could be performed at 68% of maximum aerobic capacity for 1 min because of the recovery phenomenon. Many sports consist of this type of activity. According to Keul (17), metabolic and circulatory changes similar to those seen in sports can be produced using a cycle ergometer. Several studies have found that caffeine treatment increased performance time during continuous and incremental exercise (7, 10, 15). We found that ingesting 5 mglkg BW of caffeine resulted in a 29% increase in endurance time during intermittent cycling at the 85-90% load level achieved at V02max on a continuous cycle test. These findings are unique and have not been presented in any other study. The 29% increase in time to exhaustion found in the present study was greater than the 20% increase during continuous exercise reported by Costill et al. (7) using a 5-mgfkg BW dose. Other investigators have reported that higher caffeine doses produce both similar and greater increases in

6 42 / Trice and Ha ymes time to exhaustion than were found in the present study. Spriet et al. (23) reported similar increases (27%) when subjects cycled at 80% V02 with 9 mg/kg BW; Graham and Spriet (1 3) reported a 5 1% increase in cycling time at 85% V02max. Flinn et al. (11) found that a 10-mg/kg BW dose ingested 3 hr prior to an incremental cycle test produced smaller increases in caffeine-naive subjects than those found in the present study. Although data from existing caffeine-exercise studies suggest that time to exhaustion varies relative to caffeine habits, dosage, exercise intensity, and duration, 5-mg/kg BW caffeine doses have most consistently been shown to increase performance time during continuous exercise. We found that the time to exhaustion increased significantly without any significant increase in heart rate or O2 uptake between the treatments. The expected heart rate and V02 uptake differences that accompany caffeine ingestion during continuous exercise were not seen during intermittent exercise in this study (18). This may be attributed to a time lag in respiration and circulation that occurs during short intervals of high-intensity exercise and that does not allow the O2 uptake to reach a steady state (1, 2). We concluded, therefore, that the average of both recovery O2 uptake and exercise O2 uptake measures could be used to determine oxygen cost of the exercise phase of the interval. The caffeine effect on O2 cost occurred between the first and second 30- min intervals along with significant increases in serum FFA and blood glucose, and a substantial, though not significant, increase in serum glycerol levels. The lack of a significant prelpost difference in serum glycerol levels may be attributed to the fact that the postplacebo glycerol level (3.74 mgldl) of one of the subjects was higher than his caffeine glycerol level (2.50 mgtdl). We have no explanation for this phenomenon. Duplicate samples analyzed for all subjects were found to have less than 2% variability. Although diet was not strictly controlled, all subjects reported that they had fasted for 12 hr prior to testing. Higher plasma FFA levels during the caffeine treatment indicated that caffeine increased fat mobilization. We had no way of quantifying FFA utilization because glycerol levels were not significantly different. Respiratory exchange ratio (RER) could not be used as a marker of FFA utilization because the intensity of the exercise resulted in RER greater than 1.00 for all subjects. Consolazio et al. noted that it is not uncommon for the RER to reach 1.50 during 1 min of severe exercise (6). Increased glucose levels suggest that relatively little glucose was used for energy production during the caffeine treatment (20). Together, these factors suggest that caffeine inhibits glycolysis during the early stages of high-intensity, intermittent exercise. The RPE in the caffeine trial was one full point lower than in the placebo trial but was not statistically significant. Heart rate, a more consistent indicator of the amount of stress on the muscle during intermittent exercise, was also not significantly different between the two trials (9). One might contend that the differences in RPE approach statistical significance; however, when these are viewed in combination with the closely related heart rates (caffeine bpm and placebo bpm), it is reasonable to assume that there were no differences in subjective perception of exercise difficulty (Table 2). These data support our conclusion that when trained subjects ingest a 5-mg/kg BW caffeine solution instead of a placebo, their time to exhaustion increases by 29%.

7 Caffeine Ingestion / 43 References 1. Astrand, I., P. Astrand, E.K. Christensen, and R. Hedman. Intermittent muscular work. Acta Physiol. Scand. 48: , Astrand, I., P. Astrand, E.K. Christensen, and R. Hedman. Myohemoglobin as an oxygen-store in man. Acta Physiol. Scand. 48: , Borg, G. Perceived exertion as an indicator of somatic stress. Scand. J. Rehab. Med. 2:92-98, Brozek, J., F. Grande, J.T. Anderson, and A. Keys. Densitometric analysis of body composition: Revision of some quantitative assumptions. Ann. N.Y. Acad. Sci. 110: , Casal, D.C., and A.S. Leon. Failure of caffeine to affect substrate utilization during prolonged running. Med. Sci. Sports Exerc. 17: , Consolazio, C.F., R.E. Johnson, and L.J. Pecora. Physiological Measurements of Metabolic Functions in Man. New York: McGraw-Hill, Costill, D.L., G.P. Dalsky, and W.J. Fink. Effects of caffeine ingestion on metabolism and exercise performance. Med. Sci. Sports Exerc. 10: , DeVries, H.A. Physiology of Exercise. Dubuque, IA: Brown, Ekblom, B., and A.N. Goldbarg. The influence of physical training and other factors on the subjective rating of perceived exertion. Acta Physiol. Scand. 83: , Essig, D., D.L. Costill, and P.J. Van Handel. Effects of caffeine on utilization of muscle glycogen and lipid metabolism during leg ergometer cycling. Int. J. Sports Med. 1:86-90, I. Flinn, S., J. Gregory, L.R. McNaughton, S. Tristam, and P. Davies. Caffeine ingestion prior to incremental cycling to exhaustion in recreational cyclists. Int. J. Sports Med. 11: , Gollnick, P.D., R.B. Armstrong, W.L. Sembrowich, R.E. Shepherd, and B. Saltin. Glycogen pattern depletion in human skeletal muscle fibers after heavy exercise. J. Appl. Physiol. 34(5): , Graham, T.E., and L.L. Spriet. Performance and metabolic responses to a high caffeine dose during prolonged exercise. J. Appl. Physiol. 71(6): , Hage, P. Caffeine, testosterone banned for Olympians. Physician Sportsmed. 10:15-17, Ivy, J.L., D.L. Costill, W.L. Fink, and R.W. Lower. Influence of caffeine and carbohydrate feedings on endurance performance. Med. Sci. Sports Exerc. 11:6-11, Jackson, A.S., and M.L. Pollock. Generalized equations for predicting body density of men. Br. J. Nutr. 40: , Keul, J. The relationship between circulation and metabolism during exercise. Med. Sci. Sports Exerc , Knapik, J.J., M.M. Toner, W.L. Daniels, & W.J. Evans. Influences of caffeine on serum substrate changes during running in trained and untrained individuals. In Biochemistry of Exercise, H. Knuttgen, J. Vogel, & J. Poomnans (Eds.), Champaign, IL: Human Kinetics, 1983, pp McArdle, W.D., F.I. Katch, and G.S. Pechar. Comparison of continuous and discontinuous treadmill and bicycle tests for max V02. Med. Sci. Sports Exerc. 3: , McGilvery, R.W. Biochemical Concepts. Philadelphia: Sanders, 1975, pp Perkins, R., and M.H. Williams. Effects of caffeine upon maximal muscular endurance of females. Med. Sci. Sports Exerc. 3: , 1975.

8 44 / Trice and Ha ymes 22. Powers, S.K., R.J. Byrd, R. Tulley, and T. Callender. Effects of caffeine ingestion on metabolism and performance during graded exercise. Eur. J. Appl. Physiol. 50: , Spriet, L.L., D.A. MacLean, D.J. Dyck, E. Hultman, G. Cederblad, and T.E. Graham. Caffeine ingestion and muscle metabolism during prolonged exercise in humans. Am. J. Physiol. 262 (Endocrinol. Metab. 25):E891-E898, Author Nofes The contents of this publication do not necessarily reflect the views or policies of the U.S. Department of Agriculture; neither does mention of trade names, commercial products, or organizations imply endorsement by the U.S. Government. This work has been supported in part by the following awards: Florida Endowment Fund for Higher Education, federal funds from the U.S. Department of Agriculture, Agricultural Research Service Contract Number 53-3K , and a grant from the National Institutes of Health (POL-DK42618).

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