How does Caffeine help endurance athletes?
The American College of Sports Medicine (ACSM) states:
Caffeine ingestion (3-9 mg/kg body wight) prior to exercise increases performance during prolonged endurance exercise and short-term intense exercise lasting approx. 5 minutes in the laboratory.
These results are generally reported in well-trained elite or recreational athletes and t has been shown that caffeine can enhance focus during bouts of extended exhaustive exercise (think how you feel if you have a caffeinated drink even when not training!). Caffeine is ergogenic (performance-enhancing) for sustained maximal endurance exercise, and has been shown to be highly effective for time-trial performance.
As a side point, caffeine supplementation is also beneficial for high-intensity exercise, including team sports such as football and rugby, both of which are categorised by intermittent activity within a period of prolonged duration. (We have used this to great effect with The Abingdon School Boat Club over the past few seasons.)
There is a lot of literature indicating significant performance improvements in a wide range of sports when caffeine is taken: cycling, running, rowing and team sports as well as maximal muscular force and power outputs. (1)(2) - improving time to fatigue between 20-50% which is backed up by several other literatures such as (3) (23% increase in time to fatigue at 85% VO2Max), (4) (Exercise time at VO2 Max increased by 20%), (5) (1500m Running), (6) (Performance in 1500m swimming up by 1.5-1/7%), (7) (In rowing 2000m tests improvements by about 1% in men and women) and (8) (Caffeine increases the maximum force during a voluntary contraction (MVC) by 3%.)
There is no complete understanding as to what the exact reason behind caffeine’s success is. It is considered to be due to either the direct action of caffeine on the skeletal muscles or impacting the brain to reduce the perception of fatigue or increase fat use by the muscles thus sparing muscle glycogen use (but this is not proven as muscle glycogen use is unaffected (4) and there is limited evidence of whole body fat metabolism with carbohydrate sparing (9) (10) (11)). Recent studies (12) have indicated that ingesting caffeine with carbohydrate increases carbohydrate oxidation as a result of enhanced intestinal absorption of carbohydrates. As hypoglycaemia is the significant factor in limiting performance, there are clear advantages of having a greater quantity of carbohydrate oxidation! Excretion (going for a pee) is not affected by caffeine during exercise (13) nor does it increase urine production during exercise (14) although it does so at rest.
(1) Graham and Spreit 1991; Graham, T.E., Spriet, L.L. (1991). Performance and metabolic responses to a high caffeine dose during prolonged exercise. Journal of Applied Physiology 71, 2292–98.
(2) Spriet et al 1992; Spriet, L.L. MacLean, D.A., Dyck, D.J., Hultman, E., Cederblad, G., Graham, T.E. (1992). Caffeine ingestion and muscle metabolism during prolonged exercise in humans. American Journal of Physiology 262, E891–98.
(3) Pasman et al. 1995 ; Pasman, W.J., van Baak, M.A., Jeukendrup, A.E., de Haan, A. (1995). The effect of different dosages of caffeine on endurance performance time. International Journal of Sports Medicine 16, 225–.
(4) Jackman et al 1996; Jackman, M., Wendling, P., Friars, D., Graham, T. (1996). Metabolic, catecholamine, and endurance responses to caffeine during intense exercise. Journal of Applied Physiology 81, 1658–63.
(5) Wiles et al 1992; Wiles, J.D., Bird, S.R., Hopkins, J., Riley, M. (1992). Effect of caffeinated coffee on running speed, respiratory factors, blood lactate and perceived exertion during 1500m treadmill running. British Journal of Sports Medicine 26, 116–20.
(6) MacIntosh et Al 1995; MacIntosh, B.R., Wright, B.M. (1995). Caffeine ingestion and performance of a 1500-metre swim. Canadian Journal of Applied Physiology 20, 168-77.
(7) Bruce et Al (2000); Bruce, C.R., Anderson, M.E., Fraser, S.F., Stepto, N.K., Klein, R., Hopkins, W.G., Hawley, J.A. (2000). Enhancement of 2000-m rowing performance after caffeine ingestion. Medicine and Science in Sports and Exercise 32, 1958–63.
(8) Anderson et Al (2000); Anderson, M.E., Bruce, C.R., Fraser, S.F., Stepto, N.K., Klein, R., Hopkins, W.G., Hawley, J.A. (2000). Improved 2000- meter rowing performance in competitive oarswomen after caffeine ingestion. International Journal of Sports Nutrition and Exercise Metabolism 10, 464–75.
(9) Kalmar, J.M., Cafarelli, E. (1999); Kalmar, J.M., Cafarelli, E. (1999) Effects of caffeine on neuromuscular function. Journal of Applied Physiology 87, 801–08.
(10) Mohr et al. 1998; Mohr, T., Van Soeren, M., Graham, T.E., Kjaer, M. (1998). Caffeine ingestion and metabolic responses of tetraplegic humans during electrical cycling. Journal of Applied Physiology 85, 979–85.
(11) Van Soeren and Graham 1998; Van Soeren, M.H., Graham, T.E. (1998). Effect of caffeine on metabolism, exercise endurance, and catecholamine responses after withdrawal. Journal of Applied Physiology 85, 1493–501.
(12) E. Sophie et al. 2005; Sophie E. Yeo , Roy L. P. G. Jentjens , Gareth A. Wallis , Asker E. Jeukendrup (2005) Caffeine increases exogenous carbohydrate oxidation during exercise. Journal of Applied Physiology 844-850
(13) Van der Merwe et al 1992; Van der Merwe, P.J., Luus, H.G., Barnard, J.G. (1992). Caffeine in sport: Influence of endurance exercise on the urinary caffeine concentration. International Journal of Sports Medicine 13, 74–76.
(14) Wemple, Lamb et al 1997; Wemple, R.D., Lamb, D.R., McKeever, K.H. (1997). Caffeine vs caffeine-free sports drinks: Effects on urine production at rest and during prolonged exercise. International Journal of Sports Medicine 18, 40–46.