Caffeine and sport: role of physical exercise upon elimination.
Urinary excretion of caffeine in two populations (men and women) of cyclotourists was measured, at rest and during exercise, after oral administration of 350 mg of caffeine in aqueous solution. The so-called "total metabolites", as measured by the EMIT test, were also determined, as well as urinary creatinine. At rest, elimination in relation to body weight was identical in men and women. During exercise a fivefold decrease in the female and twofold decrease in the male populations were observed. After exercise, caffeine elimination was greater than during the physical trial but remained lower for women than for men. "Total metabolites" excretion showed evidence for a slowing of caffeine catabolism during exercise and a restart of it after exercise. The caffeine content of beverages varies considerably from one country to another, depending on local customs, so that caffeine intake may be highly variable. Our results lead us to query the validity of the upper authorized official limit for urinary caffeine (12 micrograms.ml-1) in doping controls. The nature of the sporting event, sex, weight, and sampling delay after exercise are all factors that argue against the utilization of a unique standard.