THE ROLE OF CARNITINE AND CARNITINE SUPPLEMENTATION DURING EXERCISE IN MAN AND IN INDIVIDUALS WITH SPECIAL NEEDS

Carnitine is critical for normal skeletal muscle bioenergetics. Carnit ine has a dual role as it is required for long-chain fatty acid oxidat ion, and also shuttles accumulated acyl groups out of the mitochondria . Muscle requires optimization of both of these metabolic processes du ring peak exercise performance. Theoretically, carnitine availability may become limiting for either fatty acid oxidation or the removal of acyl-CoAs during exercise. Despite the theoretical basis for carnitine supplementation in otherwise healthy persons to improve exercise perf ormance, clinical data have not demonstrated consistent benefits of ca rnitine administration. Additionally, most of the anticipated metaboli c effects of carnitine supplementation have not been observed in healt hy persons. The failure to demonstrate clinical efficacy of carnitine may reflect the complex pharmacokinetics and pharmacodynamics of carni tine supplementation, the challenges of clinical trial design for perf ormance endpoints, or the adequacy of endogenous carnitine content to meet even extreme metabolic demands in the healthy state. In patients with end stage renal disease there is evidence of impaired cellular me tabolism, the accumulation of metabolic intermediates and increased ca rnitine demands to support acylcarnitine production. Years of nutritio nal changes and dialysis therapy may also lower skeletal muscle carnit ine content in these patients. Preliminary data have demonstrated bene ficial effects of carnitine supplementation to improve muscle function and exercise capacity in these patients. Peripheral arterial disease (PAD) is also associated with altered muscle metabolic function and en dogenous acylcarnitine accumulation. Therapy with either carnitine or propionylcarnitine has been shown to increase claudication-limited exe rcise capacity in patients with PAD. Further clinical research is need ed to define the optimal use of carnitine and acylcarnitines as therap eutic modalities to improve exercise performance in disease states, an d any potential benefit in healthy individuals.