The primary aim of this review was to critically analyze the existing literature to elucidate the potential of caffeine to enhance short-term high-intensity exercise performance. It is well known that acute caffeine ingestion improves endurance performance, yet existing data regarding caffeine's effect on exercise dependent on nonoxidative metabolism are equivocal. The PEDro scale (58) was used to systematically analyze the validity of existing studies. Results revealed that 54-65% of studies demonstrate improved performance as a result of caffeine intake. The mean improvement in performance ranged from 6.5 to 9.4%, although the variability across studies was sizable. This suggests that only some individuals may experience improved performance with acute caffeine intake.
Caffeine ingested in capsule or powder form and as a constituent in energy drinks or supplements was shown to be ergogenic (Tables 1 and 2) for various high-intensity exercise protocols such as resistance training, sprinting, or activities simulating team sports. The lowest ergogenic caffeine doses for short-term high-intensity exercise were ingested as gum (9) (100 mg) or as part of a supplement (8). Nevertheless, the supplement ingested in the study of Beck et al. (8) did not augment 1RM strength in untrained men (7). Unpublished data (13) from a double-blind crossover study in strength-trained men reveal no change in knee extension/flexion torque, total work, or power output when a 2 mg·kg−1 dose of caffeine was ingested 70 minutes before “all-out” isokinetic dynamometry vs. a higher dose (5 mg·kg−1) or placebo. These data corroborate a previous study (48) in untrained men showing no effect of caffeine (300 and 600 mg) on peak torque. Intake of pure caffeine in doses from 3 to 6 mg·kg−1 has been shown to improve performance in team sports (15,65,67), resistance training (43,48,76), and sprint/power-based activity (3,18,60). Overall, lower doses typically ingested via commercially available energy drinks or supplements seem to be as effective as higher doses and may minimize onset of negative symptoms experienced with doses greater than 6 mg·kg−1 that are deleterious to training or athletic performance.
One potential explanation for the equivocal data regarding caffeine's ability to alter high-intensity exercise may be differences in subjects' training status. Of the studies revealing a significant improvement in short-term high-intensity exercise performance, many (9,19,42,49,72,76) included trained athletes (competitive cyclists, football players, elite athletes, and competitive swimmers) and not untrained, recreationally active, or strength-trained subjects who are typically college students. It is likely that athletes have greater motivation to perform fatiguing exercise and can provide more consistent performance day-to-day (12), which may reduce variability and thus increase statistical power. In many studies (32,49,76), subjects were low-caffeine consumers (<100 mg per day), which may potentiate the ergogenic effect of the drug compared with subjects tolerant to the effects of caffeine (50). However, further study is needed to elucidate this possibility.
An additional explanation is that like creatine, there may be individual “responders” and “nonresponders” to the effects of caffeine during short-term exercise. This may be related to caffeine habituation, although there is evidence (32,34) that caffeine tolerance does not affect subsequent endurance performance. To our knowledge, this has not been tested during short-term high-intensity exercise. In 1 study in 22 strength-trained men (5), 12 men lifted more weight on the 1RM bench press and 11 on the leg press, respectively, with caffeine (6 mg·kg−1), yet 5 and 8 men lifted more weight in the placebo trial. Similar individual variability in performance in response to acute caffeine intake was also observed in men completing resistance training (43). Unpublished data (70) in 14 strength-trained men revealed that 6 of 9 men labeled as “responders” expressed chronic caffeine intakes greater than 225 mg per day, although there was no relationship between caffeine concentration and magnitude of performance improvements. To further explore this discrepancy, scientists should regularly assess caffeine concentration in studies in which changes in short-term exercise performance are examined. However, this measurement is not frequently obtained in the majority of research investigating ergogenic effects of caffeine for short-term high-intensity exercise performance.
Recent data suggest that variations in genotype may alter caffeine metabolism and potentially magnitude of performance in response to caffeine ingestion. Caffeine is metabolized in the liver by cytochrome P450 1A2 (14), which shows marked variability between individuals (40). A single substitution in the gene causes some persons to be slow caffeine metabolizers, whereas those who are homozygous for the allele metabolize caffeine more rapidly (66). A recent report (21) demonstrated that habitual caffeine consumption is related to these genotypes, which may explain the discrepancy in individual responses to caffeine's physiological effects. However, no study has simultaneously examined the effect of differences in genotype on high-intensity exercise performance after caffeine intake.
Purported mechanisms of caffeine's ergogenic effects during high-intensity exercise are demonstrated in Figure 1. Early data (22,44) revealed that caffeine increased lipolysis and spared muscle glycogen during endurance exercise. In contrast, other studies (35,45) revealed that caffeine does not spare glycogen. High-intensity short-term exercise is not limited by carbohydrate availability, so other mechanisms must explain the ergogenic effect of caffeine.
An alternative site for caffeine's ergogenic effects may lie in the brain. Davis et al. (25) reported that caffeine delays fatigue via stimulation of the CNS by acting as an adenosine antagonist. Adenosine, a cellular component that increases with muscular contraction, inhibits neuron excitability and synaptic transmission via binding to its receptors (52), leading to decreased arousal and increased sleep (62). In male rats, run time to fatigue was 60% longer with caffeine vs. an adenosine agonist (25). Adenosine receptors exist primarily in type I fibers (37), which may decrease the likelihood of performance gains in activities dependent on type II fibers, such as heavy resistance training or sprinting. Consequently, it is unknown if enhanced short-term high-intensity exercise performance occurs via adenosine antagonism.
Acute caffeine ingestion also modifies perceptual responses that may alter performance. In a meta-analysis (27) of 21 studies using a placebo-controlled double-blind design, data revealed that caffeine decreased rating of perceived exertion (RPE) by 5.6% during prolonged exercise, which explained approximately 33% of improved performance. However, RPE assessment may not apply to the high-intensity intermittent nature of team sports or activities such as sprinting and/or resistance training in which recording exertion during a brief intense exercise bout is impractical. RPE recorded at the completion of knee extension and biceps curls was similar between caffeine and placebo (46). Unpublished data (70) in strength-trained men show no difference in RPE (11) during completion of 40 repetitions of 1-leg knee extension and flexion at 180°·s−1 after ingestion of a low (2 mg·kg−1) (5.36 ± 1.57) or moderate dose (5 mg·kg−1) (5.46 ± 1.51) of caffeine vs. placebo (5.27 ± 1.79). Overall, caffeine does not seem to alter RPE during or at completion of short-term intense exercise, although it may be due to challenges with recording RPE during exercise. Because of the paucity of data, further investigation is merited.
An effect of caffeine on psychological function is also plausible, as it alters the CNS by promoting serotonin release, increasing sympathetic activity, and decreasing the activity of inhibitory neurons due to adenosine antagonism (69). This may explain the reduced tiredness and improved mood and alertness shown with acute caffeine ingestion (41). An intriguing hypothesis is that compared with placebo, caffeine may reverse the serious withdrawal effects, such as lethargy, irritability, and headaches, reported with 24- to 48-hour caffeine abstention as commonly required in scientific protocols. Data from a recent study (70) revealed improved resistance training performance in 67% of heavy caffeine users (>225 mg per day) vs. men with lower habitual intakes (∼125 mg per day) who typically performed better in the placebo condition. These men commonly reported that they felt “less tired” and had “more energy” in the caffeine trial, although only 28% of subjects correctly identified the caffeine treatment. Further research using psychological scales quantifying mood before and during bouts of high-intensity exercise is warranted to further explore this potential mechanism.
In summary, the exact mechanism explaining ergogenic effects of caffeine for short-term high-intensity exercise is relatively unknown, especially at physiological caffeine concentrations. It is likely multifactorial with central factors such as adenosine antagonism the most probable mechanism, yet enhanced performance may also be related to alterations in perceived exertion, reaction time, cognition, and/or mood.
There is a paucity of research investigating efficacy of caffeine in sports including sprinting, track and field, football, and hockey. Any benefit of chronic caffeine intake for completion of day-to-day training, and subsequent performance at games or meets, also requires further investigation.
The focus of this review was to critically examine studies investigating the effect of acute caffeine ingestion on performance in activities including sprinting, all-out cycling, team sports, and resistance training that are dependent on nonoxidative metabolism. Data reveal that:
Gratitude is expressed to many participants who completed various studies in the author's laboratory. Furthermore, this work could not have occurred without the assistance of an outstanding collection of undergraduate students. The authors also thank the reviewers for thorough comments that improved the quality of this review. The results of the present study do not constitute endorsement of the product by the authors or the National Strength and Conditioning Association.
References
1. Alford, C, Cox, H, and Wescott, R. The effects of Red Bull energy drink on human performance and mood.
Amino Acids 21: 139-150, 2001.
2. Andersen, JF, Jacobs, DR, Carlsen, MH, and Blomoff, R. Consumption of coffee is associated with reduced risk of death attributed to inflammatory and cardiovascular diseases in the Iowa Women's Health Study.
Am J Clin Nutr 83: 1039-1046, 2006.
3. Anselme, F, Collomp, K, Mercier, B, Ahmaidi, S, and Prefaut, C. Caffeine increases maximal
anaerobic power and blood lactate concentration.
Eur J Appl Physiol 65: 188-191, 1992.
5. Astorino, TA, Firth, K, and Rohmann, RL. Effect of caffeine ingestion on one-repetition maximum
muscular strength.
Eur J Appl Physiol 102: 127-132, 2008.
6. Beaven, CM, Hopkins, WG, Hansen, KT, Wood, MR, Cronin, JB, and Lowe, TE. Dose effect of caffeine on testosterone and cortisol responses to resistance exercise.
Int J Sport Nutr Exerc Metab 18: 131-141, 2008.
7. 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 exhaustion.
J Strength Cond Res 22: 1654-1658, 2008.
8. Beck, TW, Housh, TJ, Schmidt, RJ, Johnson, GO, Housh, DJ, Coburn, JW, and Malek, MH. The acute effects of a caffeine-containing supplement on strength, muscular endurance, and anaerobic capabilities.
J Strength Cond Res 20: 506-510, 2006.
9. Bliss, MV, Bellar, D, Kamimori, GH, Glickman, EL, Barkley, JE, Ryan, EJ, and Bellar, A. The effect of caffeine supplementation on performance in the standing shot put throw.
Med Sci Sports Exerc 40: S2036, 2008.
10. Bond, V, Gresham, K, McRae, J, and Tearney, RJ. Caffeine ingestion and isokinetic strength.
Br J Sports Med 20: 135-137, 1986.
11. Borg, GA. Psychophysical bases of perceived exertion.
Med Sci Sports Exerc 14: 377-381, 1982.
12. Burke, LM. Caffeine and sports performance.
Appl Physiol Nutr Metab 33: 1319-1334, 2008.
13. Burnett, TR, Terzi, M, and Astorino, TA. Effect of caffeine ingestion on muscle performance during repeated bouts of knee extension and flexion.
Med Sci Sports Exerc 41: S2566, 2009.
14. Butler, MA, Iwasaki, M, Guengerich, FP, and Kadlubar, F. Human cytochrome P450A (P-4501A2), the phenacetin
O-deethylase, is primarily responsible for the hepatic 3-demethylation of caffeine and N-oxidation of carcinogenic arylamines.
Proc Natl Acad Sci U S A 86: 7696-7700, 1989.
15. Carr, A, Dawson, B, Schneiker, K, Goodman, C, and Lay, B. Effect of caffeine supplementation of repeated sprint running performance.
J Sports Med Phys Fitness 48: 472-478, 2008.
16. Clausen, T. Na+-K+ pump regulation and skeletal muscle contractility.
Physiol Rev 83: 1269-1324, 2003.
17. Cole, KJ, Costill, DL, Starling, RD, Goodpaster, BH, Trappe, SW, and Fink, WJ. Effect of caffeine ingestion on perception of effort and subsequent work production.
Int J Sports Nutr 6: 14-23, 1996.
18. Collomp, K, Ahmaidi, S, Audran, M, Chanal, JL, and Prefaut, C. Effects of caffeine ingestion on performance and anaerobic metabolism during the Wingate test.
Int J Sports Med 12: 439-443, 1991.
19. Collomp, K, Ahmaidi, S, Chatard, JC, Audran, M, and Prefaut, C. Benefits of caffeine ingestion on sprint performance in trained and untrained swimmers.
Eur J Appl Physiol 64: 377-380, 1992.
20. Cook, DB, O'Connor, PJ, Eubanks, SA, Smith, JC, and Lee, M. Naturally occurring muscle pain during exercise: Assessment and experimental evidence.
Med Sci Sports Exerc 29: 999-1012, 1997.
21. Cornelis, MC, El-Sohemy, A, and Campos, H. Genetic polymorphism of the
adenosine A
2A receptor is associated with habitual caffeine consumption.
Am J Clin Nutr 86: 240-244, 2007.
22. Costill, DL, Dalsky, GP, and Fink, WJ. Effects of caffeine on metabolism and exercise performance.
Med Sci Sports 10: 155-158, 1978.
23. Cox, GR, Desbrow, B, Montgomery, PG, Anderson, ME, Bruce, CR, Macrides, TA, Martin, DT, Moquin, A, Roberts, A, Hawley, JA, and Burke, LM. Effect of different protocols of caffeine intake on metabolism and endurance performance.
J Appl Physiol 93: 990-999, 2002.
24. Crowe, MJ, Leicht, AS, and Spinks, WL. Physiological and cognitive responses to caffeine during repeated, high-intensity exercise.
Int J Sport Nutr Exerc Metab 16: 528-544, 2006.
25. Davis, JM, Zhao, Z, Stock, HS, Mehl, KA, Buggy, J, and Hand, GA. Central nervous system effects of caffeine and
adenosine on fatigue.
Am J Physiol 284: R399-R404, 2003.
26. Desbrow, B and Leveritt, M. Well-trained endurance athletes' knowledge, insight, and experience of caffeine use.
Int J Sport Nutr Exerc Metab 17: 328-339, 2007.
27. Doherty, M and Smith, PM. Effects of caffeine ingestion on rating of perceived exertion during and after exercise: A meta-analysis.
Scand J Med Sci Sports 15: 69-78, 2005.
28. Doherty, M, Smith, PM, Hughes, M, and Davison, R. Caffeine lowers perceptual response and increases power output during high-intensity cycling.
J Sports Sci 22: 637-643, 2004.
29. Engels, HJ, Wirth, JC, Celik, S, and Dorsey, JL. Influence of caffeine on metabolic and cardiovascular functions during sustained light intensity cycling and at rest.
Int J Sports Nutr 9: 361-370, 1999.
30. Escohotado, A and Symington, K.
A Brief History of Drugs: From the Stone Age to the Stoned Age. South Paris, ME: Park Street Press, 1999.
31. Forbes, SC, Candow, DG, Little, JP, Magnus, C, and Chilibeck, PD. Effect of Red Bull energy drink on repeated Wingate cycle performance and bench-press muscle endurance.
Int J Sport Nutr Exerc Metab 17: 433-444, 2007.
32. Glaister, M, Howatson, G, Abraham, CS, Lockey, RA, Goodwin, JE, Foley, P, and McInnes, G. Caffeine supplementation and multiple sprint running performance.
Med Sci Sports Exerc 40: 1835-1840, 2008.
33. Gliottoni, RC and Motl, RW. Effect of caffeine on leg-muscle pain during intense cycling exercise: Possible role of anxiety sensitivity.
Int J Sport Nutr Exerc Metab 18: 103-115, 2008.
34. Graham, TE. Caffeine and exercise: Metabolism, endurance, and performance.
Sports Med 31: 785-807, 2001.
35. Graham, TE, Helge, JW, MacLean, DA, Kiens, B, and Richter, EA. Caffeine ingestion does not alter carbohydrate or fat metabolism in human skeletal muscle during exercise.
J Physiol 529: 837-847, 2000.
36. Graham, TE, Hibbert, E, and Sathasivam, P. Metabolic and exercise endurance effects of coffee and caffeine ingestion.
J Appl Physiol 85: 883-889, 1998.
37. Greer, F, Graham, TE, and Nagy, LE. Characterization of
adenosine receptors in rat skeletal muscle.
Can J Appl Physiol 22: 23P, 1997.
38. Greer, F, McLean, C, and Graham, TE. Caffeine, performance, and metabolism during repeated Wingate exercise tests.
J Appl Physiol 85: 1502-1508, 1998.
39. Greer, F, Morales, J, and Coles, M. Wingate performance and surface EMG frequency variables are not affected by caffeine ingestion.
Appl Physiol Nutr Metab 31: 597-603, 2006.
40. Gu, L, Gonzalez, FJ, Kalow, W, and Tang, BK. Biotransformation of caffeine, paraxanthine, theobromine, and theophylline by cDNA-expressed human CYP1A2 and CYP2E1.
Pharmacogenetics 2: 73-77, 1992.
41. Hewlett, P and Smith, A. Effects of repeated doses of caffeine on performance and alertness: New data and secondary analyses.
Hum Psychopharmacol 22: 339-350, 2007.
42. Hoffman, JR, Ratamess, NA, Ross, R, Shanklin, M, Kang, J, and Faigenabum, AD. Effect of a pre-exercise energy supplement on the acute hormonal response to resistance exercise.
J Strength Cond Res 22: 874-882, 2008.
43. Hudson, GM, Green, JM, Bishop, PA, and Richardson, MT. Effects of caffeine and aspirin on light resistance training performance, perceived exertion, and pain perception.
J Strength Cond Res 22: 1950-1957, 2008.
44. Ivy, JL, Costill, DL, Fink, WJ, and Lower, RW. Influence of caffeine and carbohydrate feedings on endurance performance.
Med Sci Sports 11: 6-11, 1979.
45. Jackman, M, Wendling, P, Friars, D, and Graham, TE. Metabolic, catecholamine, and endurance responses to caffeine during intense exercise.
J Appl Physiol 81: 1658-1663, 1996.
46. Jacobs, I, Pasternak, H, and Bell, DG. Effects of ephedrine, caffeine, and their combination of muscular endurance.
Med Sci Sports Exerc 35: 987-994, 2003.
47. Jacobson, BH and Edgley, BM. Effects of caffeine on simple reaction time and movement time.
Aviat Space Environ Med 58: 1153-1156, 1987.
48. Jacobson, BH and Edwards, SW. Influence of two levels of caffeine on maximal torque at selected angular velocities.
J Sports Med Phys Fitness 31: 147-153, 1991.
49. Jacobson, BH, Weber, MD, Claypool, I, and Hunt, LE. Effect of caffeine on maximal strength and power in elite male athletes.
Br J Sports Med 26: 276-280, 1992.
50. Kalmar, JM and Cafarelli, E. Effects of caffeine on neuromuscular function.
J Appl Physiol 87: 801-808, 1999.
51. Kovacs, EMR, Stegen, JHCH, and Brouns, F. Effect of caffeinated drinks on substrate metabolism, caffeine excretion, and performance.
J Appl Physiol 85: 709-715, 1998.
52. Latini, S and Pedata, F.
Adenosine in the central nervous system: Release mechanisms and extracellular concentrations.
J Neurochem 79: 463-484, 2001.
53. McLellan, TM and Bell, DG. The impact of prior coffee consumption on the subsequent ergogenic effect of anhydrous caffeine.
Int J Sport Nutr Exerc Metab 14: 698-708, 2004.
54. Meyers, BM and Cafarelli, E. Caffeine increases time to fatigue by maintaining force and not by altering firing rates during submaximal isometric contractions.
J Appl Physiol 99: 1056-1063, 2005.
55. Motl, RW, O'Connor, PJ, and Dishman, RK. Effect of caffeine on perceptions of leg muscle pain during moderate intensity cycling exercise.
J Pain 4: 316-321, 2003.
56. Paluska, SA. Caffeine and exercise.
Curr Sports Med Rep 2: 213-219, 2003.
57. Paton, CD, Hopkins, WG, and Vollebregt, L. Little effect of caffeine ingestion on repeated sprints in team-sports athletes.
Med Sci Sports Exerc 33: 822-825, 2001.
59. Plaskett, CJ and Cafarelli, E. Caffeine increases endurance and attenuates force sensation during submaximal isometric contractions.
J Appl Physiol 91: 1535-1544, 2001.
60. Pruscino, CL, Ross, MLR, Gregory, JR, Savage, B, and Flanagan, TR. Effects of sodium bicarbonate, caffeine, and their combination on repeated 200-m freestyle performance.
Int J Sport Nutr Exerc Metab 16: 116-130, 2008.
61. Rivers, WHR and Webber, HN. The action of caffeine on the capacity for muscular work.
J Physiol 36: 33-47, 1907.
62. Rogers, NL and Dinges, DF. Caffeine: Implications for alertness in athletes.
Clin Sports Med 24: e1-e13, 2005.
63. Rosser, JI, Walsh, B, and Hogan, MC. Effect of physiological levels of caffeine on Ca
2+ handling and fatigue development in
Xenopus isolated single myofibers.
Am J Physiol 296: R1512-17, 2009.
64. Sasche, C, Brockmoller, J, Bauer, S, and Roots, I. Functional significance of a C to A polymorphism in intron 1 of the cytochrome P450 1A2 (CYP1A2) gene tested with caffeine.
Br J Clin Pharmacol 47: 445-449, 1999.
65. Schneiker, KT, Bishop, D, Dawson, B, and Hackett, LP. Effects of caffeine on prolonged intermittent-sprint ability in team-sport athletes.
Med Sci Sports Exerc 38: 578-585, 2006.
66. Sokmen, B, Armstrong, LE, Kraemer, WJ, Casa, DJ, Dias, JC, Judelson, DA, and Maresh, CM. Caffeine use in sports: Considerations for the athlete.
J Strength Cond Res 22: 978-986, 2008.
67. Stuart, GR, Hopkins, WG, Cook, C, and Cairns, SP. Multiple effects of caffeine on simulated high-intensity team-sport performance.
Med Sci Sports Exerc 37: 1998-2005, 1995.
68. Tarnopolsky, MA. Effect of caffeine on the neuromuscular system-Potential as an
ergogenic aid.
Appl Physiol Nutr Metab 33: 1284-1289, 2008.
69. Tarnopolsky, MA and Cupido, C. Caffeine potentiates low-frequency skeletal muscle force in habitual and nonhabitual caffeine consumers.
J Appl Physiol 89: 1719-1724, 2000.
70. Terzi, M, Burnett, TR, Caraveo, M, and Astorino, TA. Effect of caffeine ingestion on leg pain during maximal knee extension exercise.
Med Sci Sports Exerc 41: S1845, 2009.
71. Van Handel, P. Caffeine. In:
Ergogenic Aids in Sport. Williams, MH, ed. Champaign, IL: Human Kinetics, 1983. pp. 128-163.
72. Wiles, JD, Coleman, D, Tegerdine, M, and Swaine, IL. The effects of caffeine ingestion on performance time, speed, and power during a laboratory-based 1 km cycling time-trial.
J Sports Sci 24: 1165-1171, 2006.
73. Williams, JH, Barnes, WS, and Gadberry, WL. Influence of caffeine on force and EMG in rested and fatigued muscle.
Am J Phys Med 66: 169-183, 1987.
74. Williams, AD, Cribb, PJ, Cooke, MB, and Hayes, A. The effect of ephedra and caffeine on maximal strength and power in resistance-trained athletes.
J Strength Cond Res 22: 464-470, 2008.
75. Wong, K, Martin, BJ, Volland, L, Rohmann, RL, and Astorino, TA. Effect of caffeine ingestion on resistance training performance [abstract]. Presented at: Southwest ACSM Meeting; San Diego, CA, November 12, 2008.
76. Woolf, KW, Bidwell, WK, and Carlson, AG. The effect of caffeine as an
ergogenic aid in anaerobic exercise.
Int J Sport Nutr Exerc Metab 18: 412-429, 2008.