ABSTRACT

Background/theoretical basis Interest in L-carnitine as a potential ergogenic aid for sport performance spans over 30 years. During this time there have been many human and animal studies and reviews published. While interest in the topic has fluctuated alongside the positive and negative results of these studies, more recently, interest has increased again due to a number of positive observations on substrate metabolism in human exercise studies. The early studies conducted in the 1980s and 1990s examining carnitine ingestion and infusion typically investigated short-duration supplementation either from acute doses administered a few hours before exercise or from doses administered over 4 to 6 weeks of daily ingestion. Several of these early studies suggested an ergogenic effect of carnitine on variables related to sport and exercise performance, such as increased maximal aerobic capacity (VO2max), increased estimates of whole body fat oxidation during exercise, reduced blood lactate accumulation during exercise, maintenance of muscle carnitine content with training, and improved recovery from exercise. However, these observations were countered by a similar number of studies demonstrating no beneficial effects on these markers of performance. The first section of this chapter will aim to provide an overview of these early observations and highlight the equivocal outcomes from the many studies.