Caffeine can be a powerful performance enhancer in sport and exercise. Here, we review the literature into its effects and mechanisms, as well as suggested dosing.
The literature is largely unanimous in the benefit of caffeine supplementation for physical performance. Graham (2001) found this effect at ”…levels that are considerably lower than the acceptable limit of the International Olympic Committee.”
Effects of Caffeine on Exercise Performance:
The physical effects of caffeine on the body have been widely researched as they relate to endurance, with evidence to support the fact that “caffeine does not improve maximal oxygen capacity directly, but could permit the athlete to train at a greater power output and/or to train longer” and “caffeine ingestion prior to prolonged exercise delays fatigue.” (Graham, 2001). The same study found these beneficial effects in exercise bouts as short at 60 seconds and as long as two hours. Dodd (1993) found the greatest benefits to “…prolonged (>30 min), moderate intensity (≈75 to 80% VȮ2max) exercise”.
The effects are considerable, with Doherty (2004) reporting an average improvement (versus a placebo) of “…12.3% for endurance, graded, and short-term exercise, with endurance exercise receiving the greatest effect.”
Less research has been undertaken on the effects of caffeine on strength. Dodd et. al. (1993) however, reported an “…increased force development in isolated skeletal muscle.” Graham (2001) found no effect on maximal strength ability. This study did however provide evidence of a resistance to muscular fatigue, resulting in an increase in localised muscular stamina.
Mechanisms:
The reasons for the ergogenic effects of caffeine are poorly understood, with several theories existing.
The “…popular theory that it enhances fat oxidation and spares muscle glycogen has very little support and is an incomplete explanation at best” (Graham, 2001). This same study suggests “Caffeine may work, in part, by creating a more favourable intracellular ionic environment in active muscle. This could facilitate force production by each motor unit.”
Dodd (1993) proposes numerous mechanisms, including a “…caffeine-mediated glycogen sparing effect secondary to an increased rate of lipolysis…” Graham (1994) echoed this theory that changes are “…associated with muscle glycogen sparing and elevated plasma epinephrine…” Dodd states, “Growing evidence suggests that inhibition of adenosine receptors is one of the most important, if not the most important, mechanism to explain the physiological effects of caffeine…”
In 2000, Laurent et. al. proposed that caffeine “lowers the threshold for exercise induced endorphin and cortisol release, which may contribute to the reported benefits of caffeine on exercise endurance.”
Side Effects:
Concerns regarding the effects of caffeine on hydration and body temperature control seem unfounded, with Falk et. al. (1990) finding that “…caffeine ingestion… does not seem to disturb body fluid balance or affect thermoregulation during exercise performance.” Graham (2001) supported these findings: “There is no evidence that caffeine ingestion before exercise leads to dehydration, ion imbalance, or any other adverse effects.”
Other Variables:
The effects of caffeine on the performance of individuals who consume caffeine as a regular part of their lifestyle has been studied in great depth. In 2001, Graham suggested “…that caffeine non-users and users respond similarly and that withdrawal from caffeine may not be important.” This conflicted with the 1986 findings from Fisher et. al. (“…habitually high caffeine users acquire a tolerance to caffeine which reduces its effects during prolonged exercise…) and the 1992 findings from Bangsbo (“…habitual stimulation results in a general dampening of the epinephrine response to caffeine or exercise…”). Fisher goes on to state that “…to magnify the effect of caffeine, habitual users should withdraw from caffeine use for about 4 days.”
Weir et. al. (1987) examined the effects of caffeine on individuals who consumed a high carbohydrate diet and/or the ingestion of a single high carbohydrate meal. The found that the “…metabolic response to prolonged submaximal exercise was… not influenced by the ingestion of caffeine by subjects who had eaten a high carbohydrate diet” or by those who had ingested a high carbohydrate meal.
Dose:
Pasman et. al. (1995) studied the effects on exercise performance of 0, 5, 9 and 13mg of caffeine per kilogram of bodyweight. They found no differences “…in endurance performance between the three caffeine dosages, which indicates that no dose-response relation of caffeine and endurance performance was found.” They went on to state “Only the lowest dose of caffeine resulted in urine caffeine concentrations below the doping limit of the International Olympic Committee.” This result would imply a maximum dose of 5mg of caffeine per kilogram of bodyweight.
Bell and McLellan (2003) found that “Ingesting between 2.5mg and 5mg of caffeine per kilogram of bodyweight 60 minutes before endurance exercise increased exercise time to exhaustion for the initial exercise session…”. They also examined the longevity of this dose, and found that the benefits continued through a “…secondary bout (of exercise) five hours later without the need to redose.” This has implications for athletes competing in multiple events over the course of a day, and suggests that a single dose of 5mg/kg 60 minutes before the first event of the day is optimal.
In terms of the source of caffeine, Graham (2011) found “the ingestion of caffeine as coffee appears to be less effective than pure caffeine.”
Dodd, S.L., Herb, R.A. & Powers, S.K. Caffeine and Exercise Performance. Sports Medicine (1993) 15: 14. doi:10.2165/00007256-199315010-00003
Doherty, M. & Smith, P. M. Effects of Caffeine Ingestion on Exercise Testing: A Meta-Analysis. International Journal of Sport Nutrition and Exercise Metabolism 2004 14:6, 626-646
Bangsbo, J., Jacobsen, K., Nordberg, N., Christensen, N. J., Graham, T. Acute and habitual caffeine ingestion and metabolic responses to steady-state exercise. Journal of Applied Physiology Apr 1992, 72 (4) 1297-1303.
Bareket Falk, Ruth Burstein, Josef Rosenblum, Yair Shapiro, E. Zylber-Katz, N. Bashan. Effects of caffeine ingestion on body fluid balance and thermoregulation during exercise. Canadian Journal of Physiology and Pharmacology, 1990, 68(7): 889-892, 10.1139/y90-135.
Fisher, S.; McMurray, R.; Berry, M.; Mar, M.; Forsythe, W. Influence of Caffeine on Exercise Performance in Habitual Caffeine Users. International Journal of Sports Medicine 1986; 07(05): 276 – 280. DOI: 10.1055/s-2008-1025774
Graham, T.E. Caffeine and Exercise. Sports Med (2001) 31: 785. doi:10.2165/00007256-200131110-00002
Pasman, W. J., van Baak, M. A., Jeukendrup, A. E., de Haan, A. The Effect of Different Dosages of Caffeine on Endurance Performance Time. Int J Sports Med 1995; 16(4): 225-230.
Graham, T. E., Rush, J. W. W., van Soeren, M. H. Caffeine and Exercise: Metabolism and Performance. Canadian Journal of Applied Physiology, 1994, 19:111-138, 10.1139/h94-010
Graham, T. E., Battram, D. S., Dela, F., El-Sohemy, A., Thong, F. S. L. Does caffeine alter muscle carbohydrate and fat metabolism during exercise? Applied Physiology, Nutrition, and Metabolism, 2008, 33:1311-1318, 10.1139/H08-129
Laurent, D., Schneider, K. E., Prusaczyk, W. K., Franklin, C., Vogel, S. M., Krssak, M., Petersen, K. F., Goforth, H. W., Shulman, G. I. Effects of Caffeine on Muscle Glycogen Utilization and the Neuroendocrine Axis during Exercise. J Clin Endocrinol Metab 2000; 85 (6): 2170-2175. doi: 10.1210/jcem.85.6.6655
Weir, J., Noakes, T. D., Myburgh, K., Adams, B. A high carbohydrate diet negates the metabolic effects of caffeine during exercise. Medicine and Science in Sports and Exercise [1987, 19(2):100-105].
