CARNITINE SUPPLEMENTATION - EFFECT ON MUSCLE CARNITINE AND GLYCOGEN-CONTENT DURING EXERCISE

This study investigated the effects of L-carnitine supplementa tion on muscle carnitine and glycogen content during submaximal exercise (EX) . Triglycerides were elevated by a fat feeding (90 g fat) and 3 h late r subjects cycled for 60 min at 70% VO2max (CON). Muscle biopsies were obtained preexercise and after 30 and 60 min of EX. Blood samples wer e taken prior to and every 15 min of exercise. Subjects randomly compl eted two additional trials following 7 and 14 d of carnitine supplemen tation (6 g.d(-1)). During one of the two trials, subjects received 20 00 units of heparin 15 min prior to EX to elevate FFA(CNhep); no hepar in was administered during the other trial (CN). There were no differe nces in VO2, respiratory exchange ratio, heart rate, or g.mid(-1) of C HO and fat oxidized among the three trials. At rest serum total acid s oluble (TASC) and free (FC) carnitine increased with supplementation ( TASC; CON, 71.3 +/- 2.9;CN, 92.8 +/- 5.4; CNhep, 109.8 +/- 3.5 mu mol. l(-1)) (FC; CON, 44.1 +/- 2.7; CN, 66.1 +/- 5.3; CNhep, 77.1 +/- 4.1 m u mol.l(-1)). During EX, TASC remained stable, while FC decreased and short-chain acylcarnitine (SCAC) increased (P < 0.05). Muscle carnitin e concentration at rest was unaffected by supplemen tation. During EX, muscle TASC did not change, FC decreased, and SCAC increased signific antly in all three trials. Pre-EX and post-EX muscle glycogens were no t different. Increased availability of serum carnitine does not result in an increase in muscle carnitine content nor does it alter lipid ox idation. It appears that there is an adequate amount of carnitine pres ent within the mitochondria to support lipid oxidation.