Carnitine in muscle, serum, and urine of nonprofessional athletes: Effects of physical exercise, training, and L‐carnitine administration

Abstract

Efficient utilization of fatty acids to sustain prolonged physical efforts is thought to be dependent on the carnitine shuttle of muscle. A study has been carried out in 24 athletes (13 long-distance runners and 11 sprinters). These subjects received placebo or L-carnitine (1 g/orally b.i.d.) during a 6-month period of training. In endurance athletes, training induced lowering of total and free muscle carnitine. Increase of esterified muscle carnitine was also observed. Post-exertional overflow of acetylcarnitine and long-chain acylcarnitine, as well as reduction of the free fraction was also noticed in the blood. Fasting plasma carnitine levels, however, were not affected in carnitine-treated athletes at rest. These changes were likely related with the significantly increased urinary excretion of esterified and total carnitine which occurred after physical exercise. In the sprinters only, a decrease in free and total carnitine of muscle was detected after training. Both these potentially unfavorable effects were prevented by oral administration of L-carnitine. Our data suggest that training in endurance athletes, and to a lesser extent, in sprinters, is associated with a decrease in free and total carnitine of muscle, due to an increased overflow of short-chain carnitine esters in urine.

l-Carnitinel-tartrate supplementation favorably affects markers of recovery from exercise stress

“…During placebo, there was no change in the total carnitine response to exercise; however, free carnitine was significantly reduced at 30 and 120 min postexercise, and there was a slight increase in acetylcarnitine. A decrease in serum free carnitine and an increase in acetylcarnitine after intense exercise is in agreement with other studies that have examined carnitine responses to exercise (1,9). Although there are proportional changes in free and acetylcarnitine in muscle during exercise, it is generally accepted that the total muscle carnitine concentration is not altered during exercise and does not interact significantly with carnitine metabolism in the circulation (10).…”

Effects of Carnitine Coingested Caffeine on Carnitine Metabolism and Endurance Capacity in Athletes.

“…Our study also showed that NEC levels slightly decreased and that ASAC levels increased with a CON or CAF trial. This alternation of CAR levels was explained by the enhanced oxidation of both pyruvate and fatty acids in muscles during prolonged exercise (49). Plasma CAR concentrations at exhaustion time were significantly increased in CAR-supplemented groups.…”

Nutritional Interventions as Potential Strategy to Minimize Exercise-Induced Muscle Injuries in Sports

“…This decrease has been suggested as one of the mechanisms for the reduction of plasma fatty acid and intramuscular triacylglycerol oxidation during high-intensity exercise [91]. Accordingly most studies showed improved maximum oxygen consumption, reduced lactate accumulation, and increased high-intensity exercise performance in professional and nonprofessional athletes, especially when L-carnitine was supplemented for longer periods and at higher doses [92][93][94][95]. However, some investigations failed to show any effect of carnitine supplementation following on high-intensity training programs [96][97][98][99][100][101].…”