|
|
Caffeine
and Endurance Performance
Ellen Coleman, RD, MA, MPH © 2004
Caffeine holds a unique position in the athletic world. The
use of caffeine is restricted by the International Olympic Committee
in that urinary caffeine levels above 12 micrograms/ml are considered
illegal. However, caffeine is an integral part of many athletes'
diets and moderate caffeine doses (3-6 mg/kg) can enhance performance
in certain exercise situations. Thus, caffeine has the potential
to be a "legal" ergogenic aid.
How does caffeine enhance exercise performance? Since caffeine
enters the central nervous system and skeletal muscle, it isn't
possible to separate caffeine's central effects from it's peripheral
effects. It's also possible that different mechanisms are responsible
for performance improvement in different exercise situations
(1).
Three major theories have been proposed for the ergogenic effects
of caffeine (1). First, as a central nervous system stimulant,
caffeine increases alertness and decreases the perception of
fatigue. Caffeine may reduce the perception of effort by lowering
the neuron activation threshold, making it easier to recruit
the muscles for exercise.
Second, caffeine may increase the force of muscle contractions
by positively influencing calcium kinetics and the sodium-potassium
pump activity within the exercising muscles.
Third, caffeine may increase fat utilization and decrease carbohydrate
utilization. This is the classic or "metabolic" hypothesis.
Caffeine mobilizes free fatty acids from adipose or intramuscular
triglyceride by increasing circulating epinephrine levels. The
increased availability of free fatty acids increases fat metabolism
and decreases carbohydrate utilization. This delays glycogen
depletion and so enhances endurance performance.
Next: "Laboratory
Studies"
|
|
