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

Muscle Nerve. 1991 Jul;14(7):598-604. doi: 10.1002/mus.880140703.


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.

Publication types

  • Clinical Trial
  • Comparative Study
  • Controlled Clinical Trial

MeSH terms

  • Adult
  • Carnitine / analysis*
  • Carnitine / pharmacology*
  • Carnitine / physiology
  • Exercise / physiology*
  • Female
  • Humans
  • Male
  • Muscles / chemistry*
  • Physical Education and Training*
  • Physical Endurance / physiology
  • Running


  • Carnitine