Plasma and urine carnitine concentrations in well-trained athletes at restand after exercise. Influence of L-carnitine intake

L-carnitine is essential to cellular energy production mainly because of it s acyl- and acetyl-carrier properties. Athletes commonly take L-carnitine, which is thought to improve exercise performance. There are no reports on c arnitine plasma concentrations and carnitine excretion in short-duration ma ximal exercise in well-trained athletes taking this substance. We measured plasma and urine carnitine concentrations before and 10 min after maximal t readmill ergometry in nine well-trained sportsmen with and without oral sup plementation with 1 g L-carnitine. In athletes without L-carnitine intake, plasma free carnitine concentration decreased significantly from 45.2 +/- 5 .3 to 41.6 +/- 5.0 mu mol/l (mean +/- SD, p < 0.001) 10 min after exercise compared with baseline. In athletes with oral L-carnitine supplementation, plasma free carnitine concentration at baseline was 71.3 +/- 10.2 mu mol/l and did not change after maximal exercise (71.8 mu mol/l +/- 10.7 mu mol/l) . The elevated plasma concentration of free carnitine without decrease afte r maximal exercise in well-trained athletes taking L-carnitine could be imp ortant in view of the newly postulated direct vascular effects of L-carniti ne in improving skeletal muscle performance.