Most athletes consume caffeine beverages prior to exercise competition. Although it has no nutritional value, it does enhance performance.

Theory of Action

The exact mechanism of exercise enhancement is not known. There are 3 theories.

1. Direct effect on central nervous system. There is a direct effect of caffeine on the central nervous system which effects perceived effort or muscle contraction.

2. Direct effect on skeletal muscle. This would involve iron transport and effects on regulatory enzymes which control glycogen breakdown.

3. Metabolic theory. Caffeine enhances activity of enzymes which break down fat into fatty acids or mobilizes free-fatty acids from triglyceride. This causes an increase in fat oxidation and a decrease or sparing of carbohydrate oxidation.

Type of Exercise Performance Enhanced

Caffeine has not been shown to help sprint or anerobic performance (exercise lasting less than 2 minutes). Short term intense exercise of 5 to 20 minutes has been minimally enhanced with use of caffeine. Long term exercise or aerobic exercise has been enhanced by ingestion of caffeine.

Amount and Predictability of Enhancement

The degree of enhancement is small, usually in the 1-5% range and variable. The variability is dependent on dosage and time ingested. Optimal time is approximately 1 hour before exercise. The dosage is usually 5-6mgm/kilogram of body weight. Chronic caffeine use dampens the response.

Legal Consideration

Caffeine is a "controlled or restricted drug", and levels of greater than 12mg/ml of urine are considered illegal by the International Olympic Committee (IOC). To reach a level of greater than 12mg/ml usually require 4-5 cups of strong coffee ingested 1-1 ½ hours before testing.

Side Effects

There are several side effects to taking caffeine.

1. Decreased temperature tolerance. Thus it is not recommended to take caffeine on a hot day.

2. Nausea. This is often dose related.

3. Anxiety or "agitation".

4. Occasional cardiac palpitation. If you are subject to cardiac tachycardia, caffeine is contra indicated.