Metabolic changes induced by maximal exercise in human subjects following L-carnitine administration

Abstract In double-blind cross-over experiments, ten moderately trained male subjects were submitted to two bouts of maximal cycle ergometer exercise separated by a 3 day interval. Each subject was randomly given either l -carnitine (2 g) or placebo orally 1 h before the beginning of rach exercise session. At rest l -carnitine supplementation resulted in an increase of plasma-free carnitine without a change in acid-soluble carnitine esters. Treatment with l -carnitine induced a significant post-exercise decrease of plama lactate and pyruvate and a concurrent increase of acetylcarnitine. The determination of the individual carnitine esters in urine collected for 24 h after the placebo exercise trial revealed a decrease of acetyl carnitine and a parallel increase of a C 4 carnitine ester, probably isobutyrylcarnitine. Conversely, acetylcarnitine was strongly increased and C 4 compounds were almost suppressed in the l -carnitine loading trial. These results suggest that l -carnitine administration prior to high-intensity exercise stimulates pyruvate dehydrogenase activity, thus diverting pyruvate from lactate to acetylcarnitine formation.