The effect of oral supplementation with l-carnitine on maximum and submaximum exercise capacity

Summary

Two trials were conducted to investigate the effects of l-carnitine supplementation upon maximum and submaximum exercise capacity. Two groups of healthy, untrained subjects were studied in double-blind cross-over trials. Oral supplementation of 2 g per day l-carnitine was used for 2 weeks in the first trial and the same dose but for 4 weeks in the second trial. Maximum and submaximum exercise capacity were assessed during a continuous progressive cycle ergometer exercise test performed at 70 rpm. In trial 1, plasma concentrations of lactate and β-hydroxybutyrate were measured pre- and post-exercise. In trial 2, pre- and post-exercise plasma lactate were measured. The results of treatment with l-carnitine demonstrated no significant changes in maximum oxygen uptake ($\dot V_{O_{2\max } }$) or in maximum heart rate. In trial 1, there was a small improvement in submaximal performance as evidenced by a decrease in the heart-rate response to a work-load requiring 50% of $\dot V_{O_{2\max } }$. The more extensive trial 2 did not reproduce the significant result obtained in trial 1, that is, there was no significant decrease in heart rate at any given submaximal exercise intensity, under carnitine-supplemented conditions. Plasma metabolic concentrations were unchanged following l-carnitine, in both trials. It is concluded, that in contrast to other reports, carnitine supplementation may be of little benefit to exercise performance since the observed effects were small and inconsistent.