American Fitness Professionals & Associates

Performance Aid

Caffeine is the most commonly consumed drug in the world.  It is likely that its use will not decline any time soon because it is inexpensive, medically safe, socially acceptable, and legal (1). Caffeine may affect stimulatory receptors in the central nervous system (CNS), as well as metabolic receptors in peripheral tissues, such as skeletal muscles and may have the ability to influence psychological states and alter pain perception.(2)

One of the first studies to investigate caffeine’s effect on exercise metabolism and performance was performed by Costill et al.(3)  Subjects consumed decaffeinated coffee or decaffeinated coffee with 330 mg of caffeine 60 minutes prior to exercise.  Time to exhaustion was over 19% greater in the caffeine trial compared to the decaffeinated trial.  Erickson et al. demonstrated that caffeine supplementation prior to exercise was found to reduce muscle glycogen utilization by 30%.(4)  Spriet et al. s(5) reported a 55% decrease in muscle glycogenolysis in just the first 15 minutes of exercise during the caffeine trail.

More recent work (6) by Bell and co-workers have further substantiated the ergogenic effects of caffeine as well as how this effect can be maintained throughout the day.  In this study, nine male caffeine users performed exercise rides to exhaustion at 80% VO₂max after ingesting a placebo, 5 mg x kg^-1 of caffeine (~398 mg of caffeine for a 175 pound individual), or 2.5 mg x kg^-1 of caffeine one hour before the endurance ride. Two endurance rides were performed weekly on the same day once in the morning (AM) and five hours later in the afternoon (PM). There were four treatments:trial A representing 5-mg x kg^-1 caffeine in the AM and 2.5-mg x kg^-1 caffeine in the PM; trial B, which was placebo in both AM and PM; trial C representing 5-mg x kg^-1 caffeine in the AM and placebo in the PM; and trial D representing a placebo in the AM and 5-mg x kg^-1 caffeine in the PM. The order of the treatment trials was double blind and randomized.

Caffeine ingestion significantly increased exercise time to exhaustion in the AM by up to 14%. This effect was maintained in the PM and greater than placebo regardless of whether redosing or placebo followed the initial morning dose.  Thus, it was concluded that redosing with caffeine after exhaustive exercise in the AM was not necessary to maintain the ergogenic effect during subsequent exercise 6 h later.  From a practical standpoint, this shows that one can ingest caffeine in the morning and still derive benefits later in the day.

Based on the available science, it is evident that a dose of 5 mg caffeine per kg of body weight is needed to see performance effect.  This ergogenic effect can be seen with endurance exercise as well as sprint performance. (7)

Side Effects

It should be noted that there are various case reports on caffeine toxicity and overdose.  For instance, there is a case of a 16 year old male who ingested an estimated 6-8 grams of caffeine. This patient manifested many of the adverse effects seen in acute caffeine ingestion such as hypokalemia, elevated blood glucose, tachycardia, and agitation. Respiratory alkalosis and chest pain, which have not been previously reported to our knowledge in caffeine overdose, were also noted in this patient.(8)  There was another case of a 20-year-old bulimic woman who ingested 20 g of caffeine in a suicide attempt. After being evaluated and discharged from the emergency department, she was readmitted with electrocardiogram alterations and was discovered to have had a subendocardial infarction. According to the authors, “this case highlights the wide-ranging health consequences of eating disorders and the toxicity of caffeine overdose.” (9) The doses seen in these victims are 20 to 60 times greater than the required ergogenic dose of caffeine.  Thus, as with any drug or ergogenic aid, there is potential for abuse.

Caffeine as a dehydrating agent

In a paper by Armstrong et al. he reviewed the scientific literature to determine if indeed caffeine posed a problem vis a vis dehydration.  It is apparent that caffeine consumption stimulates a mild diuresis similar to water; however, there is no evidence of a fluid-electrolyte imbalance that is detrimental to exercise performance or health.  In fact, studies that have compared caffeine (100-680 mg) to water or placebo seldom found a statistical difference in urine volume. Additionally, tolerance to caffeine reduces the likelihood that a detrimental fluid-electrolyte imbalance will occur.  Thus, the notion that caffeine might have an eroglytic effect due to diuresis is not supported by the existing data.(10)

1.         Sinclair. C.J.D., and J.D. Geinger.  2000.  Caffeine use in sports a pharmacological review.  The Journal of Sports Medicine and Physical Fitness 40 (1): 71-77.

2.         O’Connor PJ, Motl RW, Broglio SP, Ely MR. Dose-dependent effect of caffeine on reducing leg muscle pain during cycling exercise is unrelated to systolic blood pressure. Pain 2004;109:291-8.

3.         Costill DL, Dalsky GP, Fink WJ. Effects of caffeine ingestion on metabolism and exercise performance. Med Sci Sports 1978;10:155-8.

4.         Erickson MA, Schwarzkopf RJ, McKenzie RD. Effects of caffeine, fructose, and glucose ingestion on muscle glycogen utilization during exercise. Med Sci Sports Exerc 1987;19:579-83.

5.         Spriet LL, MacLean DA, Dyck DJ, Hultman E, Cederblad G, Graham TE. Caffeine ingestion and muscle metabolism during prolonged exercise in humans. Am J Physiol 1992;262:E891-8.

6.         Bell DG, McLellan TM. Effect of repeated caffeine ingestion on repeated exhaustive exercise endurance. Med Sci Sports Exerc 2003;35:1348-54.

7.         Collomp K, Ahmaidi S, Chatard JC, Audran M, Prefaut C. Benefits of caffeine ingestion on sprint performance in trained and untrained swimmers. Eur J Appl Physiol Occup Physiol 1992;64:377-80.

8.         Leson CL, McGuigan MA, Bryson SM. Caffeine overdose in an adolescent male. J Toxicol Clin Toxicol 1988;26:407-15.

9.         Forman J, Aizer A, Young CR. Myocardial infarction resulting from caffeine overdose in an anorectic woman. Ann Emerg Med 1997;29:178-80.

10.       Armstrong LE. Caffeine, body fluid-electrolyte balance, and exercise performance. Int J Sport Nutr Exerc Metab 2002;12:189-206.