Effect of Red Bull Energy Drink

International Journal of Sport Nutrition and Exercise Metabolism,? 2007,? 17,? 433-444?  ©? 2007? Human? Kinetics,? Inc. Effect of Red Bull Energy Drink on Repeated Wingate Cycle Performance and Bench-Press Muscle Endurance Scott C. Forbes, Darren G. Candow, Jonathan P. Little, Charlene Magnus, and Philip D. Chilibeck The purpose of this study was to determine the effects of Red Bull energy drink on Wingate cycle performance and muscle endurance.Healthy young adults (N = 15, 11 men, 4 women, 21  ± 5 y old) participated in a crossover study in which they were randomized to supplement with Red Bull (2 mg/kg body mass of caffeine) or isoenergetic, isovolumetric, noncaffeinated placebo, separated by 7 d. Muscle endurance (bench press) was assessed by the maximum number of repetitions over 3 sets (separated by 1-min rest intervals) at an intensity corresponding to 70% of baseline 1-repetition maximum. Three 30-s Wingate cycling tests (load = 0. 075 kp/kg body mass), with 2 min recover y between tests, were used to assess peak and average power output.Red Bull energy drink significantly increased total bench-press repetitions over 3 sets (Red Bull = 34  ± 9 vs. placebo = 32  ± 8, P < 0. 05) but had no effect on Wingate peak or average power (Red Bull = 701  ± 124 W vs. placebo = 700  ± 132 W, Red Bull = 479  ± 74 W vs. placebo = 471  ± 74 W, respectively). Red Bull energy drink significantly increased upper body muscle endurance but had no effect on anaerobic peak or average power during repeated Wingate cycling tests in young healthy adults. Key Words: anaerobic power, caffeine, exercise Red Bull energy drink is purported to improve some aspects of performance (i. . , reaction time, concentration, and alertness) in exercising individuals (1). The primary ergogenic ingredient in Red Bull is caffeine. Acute caffeine ingestion of 2–9 mg/kg body weight during aerobic exercise increases endurance and reduces fatigue (11, 12, 25, 37, 46). Most resear ch on caffeine ingestion has focused primarily on its effects during short-term or extended aerobic exercise (23), with numerous studies supporting an ergogenic effect from caffeine on exercise time to exhaustion (17, 22, 29, 46, 48), maximal power output (32, 37), and performance time (9, 41).The effects of caffeine ingestion on anaerobic performance (i. e. , Wingate cycle power) and muscle endurance Forbes, Little, Magnus, and Chilibeck are with the College of Kinesiology, University of Saskatchewan, Saskatoon, SK, Canada S7N 5B2. Candow is with the Faculty of Kinesiology and Health Studies, University of Regina, Regina, SK, Canada S4S 0A2. ? ? 433 434 Forbes? et? al. (i. e. , total repetitions for lifting a given resistance over multiple sets) are less evident, however. Regarding anaerobic performance, Collump et al. 16) showed that caffeine ingestion (250 mg) 1 h before 100-m freestyle swimming significantly improved performance time. In addition, caffeine ingestion (250 mg) 30 min before exercise resulted in significant improvements during a maximum-power 6-s cycle sprint against various loads (2). Greer et al. (28), however, observed no improvement in maximum force output or reduced fatigue during repeated Wingate anaerobic tests with 6 mg/kg of caffeine 1 h before exercise; Collomp et al. (15) found no improvement during a single 30-s Wingate test with 5 mg/kg of caffeine 60 min before exercise; and Crowe et al. 18) found that 6 mg/kg of caffeine given 90 min before two 60-s cycling bouts had no effect on peak power or work output. Regarding muscle endurance, Kalmar and Cafarelli (35) reported that 6 mg/kg of caffeine given 1 h before exercise significantly increased submaximal isometric-contraction time. In contrast, Beck et al. (7) and Jacobs et al. (34) found no improvement in bench-press or leg-press muscle endurance (i. e. , total repetitions of lifting a weight corresponding to 70–80% one-repetition maximum [1-RM]) 60–90 min after su bjects consumed ~2. 5–4 mg/kg of caffeine.Although it is difficult to compare results across studies, possible explanations for these inconsistent findings might include the dose of caffeine used, subject training status, timing of caffeine ingestion, habitual caffeine consumption, and exercise modality. Although the mechanisms explaining the possible ergogenic effects of caffeine remain to be elucidated, plausible theories include caffeine’s ability to act as an adenosine-receptor antagonist (18, 19, 23), increase plasma epinephrine concentrations (33, 45), enhance calcium release and reuptake from the arcoplasmic reticulum (40), and alter plasma potassium concentrations (18). These mechanisms most likely occur with larger caffeine doses, and it is unclear whether smaller doses would be as effective. Recently it was found that larger doses of caffeine might have negative health consequences such as impaired glucose tolerance (6). We therefore decided to study the effe cts of a smaller dose of caffeine (2 mg/kg) in the form of Red Bull energy drink. To date, only 1 study has examined the effects of Red Bull energy drink on anaerobic exercise performance in young adults.Alford et al. (1) found a significant increase in maximum speed during an all-out cycling test after Red Bull supplementation (80 mg caffeine). Our purpose was to determine the effects of Red Bull energy drink on a more standardized test of anaerobic performance (i. e. , Wingate cycle test) and on muscle endurance (i. e. , maximal repetitions during bench-press lifting). These tests were used to simulate the demands of sports such as ice hockey that involve repeated bursts of activity or muscle endurance of both the lower and upper body.Energy-drink consumption and caffeine supplementation are very common in this type of sport (38). We hypothesized that Red Bull supplementation would increase Wingate anaerobic peak and average power and bench-press muscle endurance. Methods Particip ants Sixteen healthy physically active participants (12 men, 4 women, 24  ± 6 y old) volunteered for the study. They participated in moderate physical activity 2 or 3 Effect? of? Red? Bull? on? Athletic? Performance? ? 435 times per week and were instructed not to change their diets or physical activity patterns before or during the study.All subjects were required to fill out a Physical Activity Readiness Questionnaire, which screens for health problems that might present a risk with performance of physical activity (52). The study was approved by the University of Saskatchewan Biomedical Research Ethics Board for research in human subjects. Participants were informed of the risks and purposes of the study before they gave their written consent. Experimental Design The study used a double-blind repeated-measures crossover counterbalanced design in which participants were randomized to supplement with Red Bull or placebo and receive the opposite treatment 7 d later.All participant s were required to come to the laboratory on 2 occasions before the start of the study, once to determine their bench-press 1-RM strength and again 3 d later for familiarization with the experimental design by performing 3 sets of bench-press repetitions to fatigue (separated by 1-min rest intervals) at an intensity corresponding to 70% 1-RM, followed by three 30-s Wingate cycle tests (separated by 2-min rest intervals) at a load corresponding to 0. 075 kp/kg body mass (4). There was a 10-min rest period between the bench-press endurance tests and Wingate cycle tests.Three days after the familiarization trial, subjects were randomly assigned to supplement with Red Bull (2. 0 mg/kg caffeine) or placebo (noncaffeinated Mountain Dew, lemon juice, water) 60 min before performing repeated-bench-press endurance tests and Wingate cycle tests. Seven days after this initial supplementation and testing session, subjects returned to the laboratory and ingested the opposite supplement drink and performed the same exercises in the same order. They were instructed to refrain from caffeine for 48 h, physical activity for 24 h, and food and drink for 3 h before testing.The 7-d counterbalance was chosen to allow subjects adequate recovery between exercise tests. The 48 h of caffeine withdrawal before testing would be adequate because the half-life of caffeine is about 4–6 h (24). The dependent variables measured were bench-press endurance, peak power during repeated Wingate tests, and average power over 3 Wingate tests. Physical activity level and habitual caffeine consumption were recorded before the study through the questionnaire. The exercise tests were chosen to simulate sports that involve repeated bursts of high-intensity activity, such as ice hockey.For example, the 30-s Wingate tests with 2 min rest between tests simulate the work-to-rest ratio of typical hockey shifts. Time–motion analyses indicate skating times of 30–40 s between rest intervals of either whistle stops or time on the bench. Whistle stops last about 27 s, whereas time on the bench is about 227 s, for an average rest interval of about 2 min (27, 47). The bench-press test simulates upper body work during ice hockey, such as occurs during corner play and occasionally fighting (26).A caffeine-containing supplement is ideal to evaluate for this type of sport because caffeine-containing supplements are the most popular type of supplement ingested by ice hockey players (38). 436 Forbes? et? al. Supplementation Red Bull and the placebo were identical in caloric content, volume, and taste. Supplements were provided to each participant 60 min before exercise in an opaque water bottle and consumed in the presence of a researcher. Sixty minutes was chosen because this is the approximate time it takes for caffeine concentration to reach its peak after oral ingestion (23). The caffeine dose of 2. mg/kg was chosen because it is an approximate amount shown to increase muscl e performance (7) and reduce fatigue in young healthy adults, higher doses might be associated with impaired glucose tolerance (6), it is the maximal daily dose of commercial energy drinks considered safe by Health Canada (30), and this dose allowed our heaviest subjects to consume approximately 2 cans of Red Bull, which is the maximal amount recommended on the Red Bull label. Ingredients in the Red Bull energy drink are shown in Table 1. Muscle Strength and Endurance The procedures for determining bench-press 1-RM have previously been described (13).All bench-press testing was done on a bench-press machine (Lever chest-press machine, Winnipeg, MB, Canada). Reproducibility of our 1-RM test, expressed as a coefficient of variation, was 1. 9% (14). For bench-press muscle endurance, participants performed 3 sets of bench-press repetitions to volitional fatigue, separated by 1-min rest intervals, at an intensity corresponding to 70% 1-RM. Reproducibility of the bench-press endurance tes t was assessed by testing 15 subjects 3 d apart. The coefficient of variation was 1. 5%. Anaerobic Power Peak power and average power were assessed using repeated Wingate cycleergometer tests.Blood lactate concentration was measured at rest, immediately after each Wingate cycle test, and 2 min postexercise using an automated lactate analyzer (Accutrend Lactate, Roche Diagnostics, Mannheim, Germany) according to the manufacturer’s instructions. Ten minutes after the bench-press endurance test, each subject was positioned on the Wingate cycle ergometer, and seat height, handlebar Table 1 Red Bull Energy-Drink Ingredients Ingredient Sugar Caffeine Taurine Glucuronolactone Niacin Pantothenic acid Vitamin B6 Riboflavin Vitamin B12 Amount (per kg body mass) 0. 65 g/kg 2. 0 mg/kg 25 mg/kg 15 mg/kg 0. 45 mg/kg 0. 15 mg/kg 0. 5 mg/kg 0. 04 mg/kg 0. 025  µg/kg Effect? of? Red? Bull? on? Athletic? Performance? ? 437 height and position, and toe straps were adjusted based on the settin gs determined during the familiarization trial. Subjects were instructed to cycle at a slow pace against zero resistance for 5 min. Five seconds before data collection, they were instructed to pedal at maximal rate to ensure optimal power and force production at the beginning of the test and to continue cycling at a maximal speed for the duration of the 30-s test at a load corresponding to 7. 5% of their body mass (4). Subjects were verbally encouraged throughout the test.This procedure was repeated for 3 tests, with 2 min of active rest against zero load between tests. Reproducibility of peak and average power was determined by testing 10 subjects 3 d apart. The coefficients of variation were 4. 1% for peak power and 3. 6% for average power. Statistical Analyses A 2 (caffeine-consuming subjects vs. caffeine-naive subjects) ? 2 (supplement: Red Bull vs. placebo) ? 3 (exercise sets) ANOVA with repeated measures on the last 2 factors was used to assess differences between conditions f or benchpress repetitions and for peak and average power during the Wingate tests. A 2 (caffeine-consuming subjects vs. affeine naive subjects) ? 2 (supplement: Red Bull vs. placebo) ? 5 (blood lactate at 5 time points) ANOVA with repeated measures on the last 2 factors was used to assess changes in blood lactate concentration. To determine whether 1 familiarization trial was adequate to eliminate any effects of learning over time, we ran a 3 (set) ? 2 (time) repeatedmeasures ANOVA to determine whether there were differences across sets for Wingate tests and bench-press tests between the familiarization and placebo trials. Tukey’s post hoc tests were used to determine differences between means. Statistical significance was set at P ? 0. 05.All results are expressed as mean  ± standard deviation. Statistical analyses were carried out using Statistica, version 5. 0 (StatsSoft Inc. , Chicago). Results Of the original 16 subjects who volunteered, 15 completed the study. One mal e subject withdrew because of time constraints. Seven subjects were correct in perceiving that they were ingesting Red Bull or placebo, with the remaining subjects unsure. Before testing, 8 subjects were caffeine naive, 4 reported consuming 200 mg/d. There were no side effects reported from the exercise testing, Red Bull energy drink, or placebo.There were no time main effects or set ? time interactions between the familiarization trial and the placebo trial, indicating that the familiarization trial was adequate to eliminate any learning effects. Subjects who regularly consumed caffeine did not differ from caffeine-naive subjects for any of the tests or for their responses to Red Bull versus placebo (i. e. , there were no group ? supplement interactions). There was a supplement main effect for bench-press endurance, whereby the number of repetitions over the 3 sets was greater in the Red Bull condition than with placebo (Red Bull = 34  ± 9 vs. lacebo = 32  ± 8 repetitions over the 3 sets, P = 0. 031; Figure 1). There was a set main effect for bench-press endurance, Wingate peak power (Figure 2), and Wingate average power (Figure 3); that is, performance dropped across sets as 438 Forbes? et? al. would be expected (P < 0. 05). There were no differences between Red Bull and placebo for performance across sets during the Wingate tests (peak and average power: Red Bull = 701  ± 124 W vs. placebo = 700  ± 132 W and Red Bull = 479  ± 74 W vs. placebo = 471  ± 74 W), and there were no supplement ? et interactions for any of the exercise tests (Figures 2 and 3). There was a time main effect for blood lactate (mmol/L) during repeated Wingate tests (P < 0. 01; baseline: Red Bull: 4. 2  ± 1. 3 vs. placebo 3. 6  ± 1. 0; after test 1: Red Bull 7. 4  ± 2. 4 vs. placebo 6. 6  ± 1. 8; after Test 2: Red Bull 9. 0  ± 2. 9 vs. placebo 8. 9  ± 3. 4; after Test 3: Red Bull 9. 3  ± 4. 2 vs. placebo 8. 1  ± 4. 7; and 2 min postexercise: Red Bull 9. 2  ± 3. 0 vs. placebo 7. 9  ± 2. 4), with no differences between Red Bull and placebo (Figure 4). Post hoc analyses indicated that blood Total repetitions over 3 sets of bench press 5 40 35 30 25 20 15 10 5 0 Red Bull placebo * Figure 1 — Bench-press repetitions across sets, mean  ± standard deviation. Units are repetition number. Repetition number was determined as the total number of repetitions over 3 sets of bench-press exercise at 70% of 1-repetition maximum, 1 min of rest between sets. *Number of repetitions performed during the Red Bull condition was greater than the number of repetitions performed during the placebo condition (P = 0. 031). 850 Red Bull placebo Wingate peak power (W) 800 750 700 650 600 550 500 450 400 Set 1 Set 2Set 3 Figure 2 — Wingate peak power across sets, mean  ± standard deviation. Peak power was determined by the highest power output during each of 3 sets of 30-s Wingate tests, with 2 min of rest between tests. There were no differenc es between Red Bull and placebo conditions. There was a main effect for set, with Set 1 higher than Set 2 (P = 0. 021) and Set 2 higher than Set 3 (P < 0. 01). Effect? of? Red? Bull? on? Athletic? Performance? ? 439 700 Wingate average power (W) 650 600 550 500 450 400 350 300 250 200 Set 1 Set 2 Red Bull placebo Set 3Figure 3 — Wingate average power across sets, mean  ± standard deviation. Average power was determined during each of 3 sets of 30-s Wingate tests, with 2 min of rest between tests. There was a set main effect, with Set 1 higher than Set 2 (P < 0. 01) and Set 2 higher than Set 3 (P < 0. 01). 14 12 Red Bull placebo Lactate (mMol/L) 10 8 6 4 2 0 baseline after Set 1 after Set 2 after Set 3 2 min post Figure 4 — Blood lactate concentration before and after each set of 30-s Wingate tests (separated by 2 min of recovery) and 2 min postexercise, mean  ± standard deviation.Blood lactate values were determined from fingertip blood samples. There was a set mai n effect for lactate (P < 0. 01). Blood lactate concentration increased from baseline to after Set 1 (P < 0. 01) and from after Set 1 to after Set 2 (P = 0. 016). Lactate values after Set 2 were similar to lactate values after Set 3 and 2 min after Set 3. lactate concentration was elevated above baseline after each Wingate test and at 2 min after the last Wingate test (all P < 0. 01). Blood lactate concentration increased from baseline to after Test 1 (P < 0. 01) and from after Test 1 to after Test 2 (P = 0. 16). Lactate values after Test 2 were similar those after Test 3 and 2 min after Test 3. Discussion This is the first study to investigate the effects of Red Bull energy drink on upper body muscle endurance and anaerobic cycle performance in young adults. Results 440 Forbes? et? al. showed that Red Bull energy drink significantly increased total bench-press repetitions over 3 sets compared with placebo but had no significant effect on peak or average power or blood lactate conce ntration during repeated Wingate cycling tests. The main active ingredient in Red Bull energy drink is caffeine.Although the mechanisms explaining the ergogenic effects of caffeine are not fully known, plausible theories include the antagonism of adenosine receptors (18, 23, 42) leading to an increase in central-nervous-system activation (54) and plasma epinephrine concentrations (45), enhanced calcium release and reuptake from the sarcoplasmic reticulum (40) affecting skeletal-muscle excitation–contraction coupling (42), and the alteration of plasma potassium concentrations (18, 39). Caffeine has been shown to reduce plasma potassium levels compared with placebo during exercise (39).The increased intracellular potassium concentration coupled with lower extracellular potassium might help maintain membrane contractility during exercise (39). Our results of a greater increase in bench-press repetitions over 3 sets from Red Bull ingestion (2. 0 mg/kg), but no single set effect, expand the findings of Beck et al. (7), who found no effect of a caffeine-containing supplement (2. 4 mg/kg) on single-set bench-press repetitions. For the present study, bench-press muscle endurance was assessed by the total number of repetitions over 3 sets at 70% 1-RM separated by 1-min rest intervals.In contrast, participants in the Beck et al. (7) study performed a single set of bench-press repetitions at 80% 1-RM. Differences in supplement composition, study design (crossover vs. cross-sectional), and gender might also explain these different results. In addition, we cannot conclude with certainty that the greater increase in bench-press repetitions from Red Bull energy drink is a result solely of caffeine, because Red Bull contains other ingredients (see Table 1) such as carnitine, B vitamins, and taurine.The effectiveness of carnitine is controversial, with most studies showing no benefit but some showing a benefit for increased fat metabolism and enhanced recovery from exer cise stress (for reviews, see 10 and 36). These ergogenic effects might help during aerobic endurance exercise; however, it is doubtful that a benefit would be provided by acute supplementation before high-intensity exercise. Carnitine supplementation has no effect on high-intensity exercise performance (i. e. five 90-m swims separated by 2-min rest intervals) (53) or metabolic response to high-intensity exercise (i. e. , five 1-min cycle sprints separated by 2-min rest intervals) (5). The B vitamins are important for chronic adaptation to exercise training but most likely would have minimal influence when taken before an acute exercise session (55). Although carnitine and the B vitamins might not be ergogenic for the exercise tests used in the current study, taurine might exhibit beneficial effects.Taurine, a sulfonic amino acid found primarily in skeletal muscle (31, 44), has been shown to increase force production in skinned muscle fibers in a rodent model (3), possibly through i ncreased calcium release from the sarcoplasmic reticulum and increased calcium sensitivity for excitation–contraction coupling. Others have suggested that taurine might exhibit protective effects against cellular stress such as exercise by acting as a free-radical scavenger (49).In humans, taurine supplementation (6 g/d) significantly increased exercise time to exhaustion, VO2max, and maximal workload during cycle-ergometer exercise (56). Nonetheless, the amount of taurine administered before exercise in the current study was relatively low, ranging from 1 to 2 g. Therefore, it is doubtful that it would have significantly affected performance. Effect? of? Red? Bull? on? Athletic? Performance? ? 441 Red Bull energy drink had no effect on anaerobic power measures. These findings support those of Beck et al. 7), who found no effect from a caffeine-containing supplement on peak or average power output in young adults. Although it is unclear why these caffeine-containing supplemen ts had no greater effect on anaerobic power output compared with the findings of others (2, 16), possible explanations might include the caffeine dose used, caffeine habituation, and individual training status. The caffeine dose used in the current study (2. 0 mg/kg) and that of Beck et al. (7) of 2. 4 mg/kg might have been too low to observe an ergogenic effect on anaerobic-power measures.Regarding caffeine habituation, most subjects in the current study were caffeine naive; however, 7 of 15 subjects were caffeine users, with 4 consuming 200 mg caffeine per day. The Red Bull energy drink provided approximately an additional 150 mg caffeine. One previous study suggested that caffeine might not be ergogenic in habitual caffeine consumers as a result of caffeine saturation (50). Several studies have shown, however, that habitual caffeine intake does not affect the ergogenic benefits of caffeine (8, 20, 21, 43, 51).In agreement with these studies, we did not find any differences in res ponse to the Red Bull energy drink between caffeineconsuming subjects and caffeine-naive subjects. Finally, in examining the effects of caffeine ingestion on anaerobic performance in trained and untrained swimmers, Collump et al. (16) observed a decrease in 100-m swim time in the trained swimmers but no effect in the untrained swimmers. We suggest that the variations in subject training status might explain the lack of consistency across studies. Most studies that report positive effects from caffeine on naerobic exercise have used well-trained subjects (16, 20). The results of the current study suggest that moderately active individuals experience no anaerobic benefit from caffeine through Red Bull energy-drink ingestion. In summary, the results of the present study indicate that Red Bull energy drink increases upper body muscle endurance but has no effect on Wingate anaerobic power. Red Bull energy drink is commonly ingested in the hope that it will increase exercise performance. These findings suggest that it might be effective for individuals who perform repeated upper body exercise.Future research is needed to determine whether this increase in upper body muscle endurance will translate into improved performance in sports involving upper body muscle work. References 1. Alford, C. , H. Cox, and R. Wescott. The effects of Red Bull energy drink on human performance and mood. Amino Acids. 21:139-150, 2000. 2. Anselme, F. , K. Collump, B. Mercier, S. Ahmaidi, and C. Prefaut. Caffeine increases maxim anaerobic power and blood lactate concentration. Eur. J. Appl. Physiol. 65:188191, 1992. 3. Bakker, A. J. , and H. M. Berg.The effects of taurine on sarcoplasmic reticulum function and contractile properties in skinned skeletal muscle fibers of the rat. J. Physiol. 538:185-194, 2002. 4. Bar-Or, O. The Wingate anaerobic test: an update on methodology, reliability and validity. Sports Med. 4:381-394, 1987. 5. Barnett, C. , D. L. Costill, M. D. Vukovich, et al. Effect of L-carnitine supplementation on muscle and blood carnitine content and lactate accumulation during high-intensity sprint cycling. Int. J. Sport Nutr. 4:280-288, 1994. 442 Forbes? et? al. 6. Battram, D. S. , R. Arthur, A. Weekes, and T.E. Graham. The glucose intolerance induced by caffeinated coffee ingestion is less pronounced than that due to alkaloid caffeine in men. J. Nutr. 136:1276-1280, 2006. 7. Beck, T. W. , T. J. Housh, R. J. Schmidt, et al. 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, D. G. , I. Jacobs, and K. Ellerington. Effect of caffeine and ephedrine ingestion on anaerobic exercise performance. Med. Sci. Sports Exerc. 33:1399-1403, 2001. 9. Berglund, B. , and P. Hemmingsson.Effects of caffeine ingestion on exercise performance at low and high altitudes in cross-country skiing. Int. J. Sports Med. 3:234-236, 1982. 10. Brass, E. P. Carnitine and spor ts medicine: use or abuse? Ann. N. Y. Acad. Sci. 1033:6778, 2004. 11. Bruce, C. R. , M. E. Anderson, S. F. Fraser, et al. Enhancement of 2000-m rowing performance after caffeine ingestion. Med. Sci. Sports Exerc. 32:1958-1963, 2000. 12. Cadarette, B. S. , L. Levine, and C. L. Berube. Effects of varied dosages of caffeine on endurance exercise to fatigue. In: Biochemistry of Exercise (13th ed. International series of sport sciences), H. G. Knuttgen, J. A. Vogel, and J. Poortmans (Eds). Champaign, IL: Human Kinetics, 1982, pp. 871-876. 13. Candow, D. G. , N. C. Burke, T. Smith-Palmer, and D. G Burke. Effect of whey and soy protein supplementation combined with resistance training in young adults. Int. J. Sport. Nutr. Exerc. Metab. 16:233-244, 2006. 14. Candow, D. G. , P. D. Chilibeck, D. G. Burke, K. S. Davison, and T. S. Palmer. Effect of glutamine supplementation combined with resistance training in young men. Eur. J. Appl. Physiol. 86:142-149, 2001. 15. Collomp, K. , S. Ahmaidi, M. Audran, J. L. Chanal, and C. Prefaut. Effects of caffeine ingestion on performance and anaerobic metabolism during the Wingate test. Int. J. Sports Med. 12:439-443, 1991. 16. Collump, K. , S. Ahmaidi, J. C. Chatard, M. Audran, and C. Prefaut. Benefits of caffeine ingestion on sprint performance in trained and untrained swimmers. Eur. J. Appl. Physiol. Occup. Physiol. 64:377-380, 1992. 17. Costill, D. L. , G. P. Dalsky, and W. J. Fink. Effects of caffeine ingestion on metabolism and exercise performance. Med. Sci. Sports. 10:155-158, 1978. 18. Crowe, M. J. , A. S. Leicht, and W. L. Spinks.Physiological and cognitive responses to caffeine during repeated, high intensity exercise. Int. J. Sport Nutr. Exerc. Metab. 16:528-544, 2006. 19. Cureton, K. J. , G. L. Warren, M. L. Millard-Stafford, J. E. Wingo, J. Trilk, and M. Buyckx. Caffeinated sports drink: ergogenic effects and possible mechanisms. Int. J. Sport Nutr. Exerc. Metab. 17:35-55, 2007. 20. Doherty, M. The effects of caffeine on the maximal accumulated oxygen deficit and short-term running performance. Int. J. Sport Nutr. 8:95-104, 1998. 21. Doherty, M. , P. M. Smith, M. G. Hughes, and R. C. Davison. Caffeine lowers erceptual response and increases power output in high-intensity cycling. J. Sports Sci. 22:637643, 2004. 22. Flinn, S. , J. Gregory, L. R. McNaughton, S. Tristram, and P. Davies. Caffeine ingestion prior to incremental cycling to exhaustion in recreational cyclists. Int. J. Sports Med. 11:188-193, 1990. 23. Graham, T. E. Caffeine and exercise: metabolism, endurance and performance. Sports Med. 31:785-807, 2001. 24. Graham, T. E. Caffeine, coffee and ephedrine: impact on exercise performance and metabolism. Can. J. Appl. Physiol. 26(Suppl. ):S103-S119, 2001. 25. Graham, T. E. , and L. L. Spriet.Metabolic, catecholamine, and exercise performance responses to various doses of caffeine. J. Appl. Physiol. 78:867-874, 1995. Effect? of? Red? Bull? on? Athletic? Performance? ? 443 26. Green, H. J. Meta bolic aspects of intermittent work with specific regard to ice hockey. Can. J. Appl. Sport Sci. 4:29-34, 1979. 27. Green, H. J. , P. Bishop, M. Houston, R. McKillop, R. Norman, and P. Stothart. Timemotion and physiological assessments of ice hockey performance. J. Appl. Physiol. 40:159-163, 1976. 28. Greer, F. , C. McLean, and T. E. Graham. Caffeine, performance, and metabolism during repeated Wingate exercise tests.J. Appl. Physiol. 85:1502-1508, 1998. 29. Greer, F. , D. Friars, and T. E. Graham. Comparison of caffeine and theophylline ingestion: exercise metabolism and endurance. J. Appl. Physiol. 89:1837-1844, 2000. 30. Health Canada. It’s Your Health. Available at: http://www. hc-sc. gc. ca/iyh-vsv/alt_ formats/cmcd-dcmc/pdf/caffeine_e. pdf. Accessed December 17, 2006. 31. Huxtable, R. J. Physiological actions of taurine. Physiol. Rev. 72:101-163, 1992. 32. Ivy, J. L. , D. L. Costill, W. J. Fink, and R. W. Lower. Influence of caffeine and carbohydrate feedings on enduranc e performance. Med. Sci. Sports Exerc. 1:6-11, 1979. 33. Jackman, M. , P. Wendling, D. Friars, and T. E. Graham. Metabolic catecholamine, and endurance responses to caffeine during intense exercise. J. Appl. Physiol. 81:1658-1663, 1996. 34. Jacobs, I. , H. Pasternak, and D. G. Bell. Effects of ephedrine, caffeine, and their combination on muscular endurance. Med. Sci. Sports Exerc. 35:987-994, 2003. 35. Kalmar, J. M. , and E. Cafarelli. Effects of caffeine on neuromuscular function. J. Appl. Physiol. 87:801-808, 1999. 36. Karlic, H. , and A. Lohninger. Supplementation of L-carnitine in athletes: does it make sense? Nutrition. 0:709-715, 2004. 37. Kovacs, E. M. R. , J. H. C. H. Stegen, and F. Brouns. Effect of caffeinated drinks on substrate metabolism, caffeine excretion, and performance. J. Appl. Physiol. 85:709-715, 1998. 38. Kristiansen, M. , R. Levy-Milne, S. Barr, and A. Flint. Dietary supplement use by varsity athletes at a Canadian university. Int. J. Sport Nutr. Exerc. Metab . 15:195-210. 39. Lindinger, M. I. , T. E. Graham, and L. L. Spriet. Caffeine attenuates the exercise-induced increase in plasma [K+] in humans. J. Appl. Physiol. 74:1149-1155, 1993. 40. Lopes, J. M. , M. Aubier, J. Jardim, J. V. Aranda, and P.T. Macklem. Effect of caffeine on skeletal muscle function before and after fatigue. J. Appl. Physiol. 54:1303-1305, 1983. 41. MacIntosh, B. R. , and B. M. Wright. Caffeine ingestion and performance of a 1500 meter swim. Can. J. Appl. Physiol. 20:168-177, 1995. 42. Maridakis, V. , P. J. O’Connor, G. A. Dudley, and K. McCully. Caffeine attenuates delayed-onset muscle pain and force loss following eccentric exercise. Pain. 8:237-243, 2007. 43. McLellan, T. M. , and D. G. Bell. The impact of prior coffee consumption on the subsequent ergogenic effect of anhydrous caffeine. Int. J. Sport Nutr. Exerc.Metab. 14:698708, 2004. 44. Nieminen, M. L. , L. Tuomisto, E. Solatunturi, L. Eriksson, and M. K. Paasonen. Taurine in the osmoregulation of th e Brattleboro diabetes insipidus rat. Life Sci. 42:2137-2143, 1988. 45. Norager, C. B. , M. B. Jensent, A. Weimann, and M. R. Madsen. Metabolic effects of caffeine ingestion and physical work in 75-year old citizens. a randomized, double blind, placebo-controlled, cross-over study. Clin. Endocrinol. 65:223-228, 2006. 46. Pasman W. J. , M. A. van Baak, A. E. Jeukendrup, and A. de Haan. The effect of different dosages of caffeine on endurance performance time.Int. J. Sports Med. 16:225-230, 1995. 47. Paterson, D. H. Respiratory and cardiovascular aspects of intermittent exercise with regard to ice hockey. Can. J. Appl. Sport Sci. 4:22-28, 1979. 444 Forbes? et? al. 48. 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. 50:301-307, 1983. 49. Redmond, H. P. , P. P. Stapleton, P. Neary, and D. Bouchier-Hayes. Immuno-nutrition: the role of taurine. Nutrition. 14:599-604, 1998. 5 0. Tarnopolsky, M. A. , S. A. Atkinson, J. D.MacDougall, D. G. Sale, and J. R. Sutton. Physiological responses to caffeine during endurance running in habitual caffeine users. Med. Sci. Sports Exerc. 21:418-424, 1989. 51. Tarnopolsky, M. A. , and C. Cupido. Caffeine potentiates low frequency skeletal muscle force in habitual and nonhabitual caffeine consumers. J. Appl. Physiol. 89:1719-1724, 2000. 52. Thomas, S. , I. Reading, and R. J. Shephard. Revision of the Physical Activity Readiness Questionnaire (PAR-Q). Can. J. Sport Sci. 17:338-345, 1992. 53. Trappe, S. W. , D. L. Costill, B. Goodpaster, M. D. Vukovich, and W. J. Fink.The effects of L-carnitine supplementation on performance during interval swimming. Int. J. Sports Med. 15:181-185, 1994. 54. Williams, J. H. Caffeine, neuromuscular function and high-intensity exercise performance. J. Sports Med. Phys. Fitness. 31:481-489, 1991. 55. Woolf, K. , and M. M. Manore. B-vitamins and exercise: does exercise alter requirements? Int. J. Sport Nutr. Exerc. Metab. 16:453-484, 2006. 56. Zhang, M. , I. Izumi, S. Kagamimori, et al. Role of taurine supplementation to prevent exercise-induced oxidative stress in healthy young men. Amino Acids. 26:203-207, 2004.