The use of supplementary L-carnitine by athletes has become rather widespread over the recent years even in the absence of unequivocal results from human experimental studies that might support this practice. To justify the above procedure, the most commonly purported reasons are that L-carnitine administration could hypothetically: 1. increase lipid turnover in working muscles leading to glycogen saving and, as a consequence, allow longer performances for given heavy work loads; 2. contribute to the homeostasis of free and esterified L-carnitine in plasma and muscle, the allegation being that the levels of one or more of these compounds may decrease in the course of heavy repetitive exercise. A critical survey of the literature on carnitine metabolism in healthy humans at exercise does not appear to be available. The authors are of the opinion that this paper, besides shedding light into some relevant aspects of energy turnover in muscle, could also be of practical use not only for the physiologists but particularly for the Sport Medicine practitioners.