EFFECT OF L-CARNITINE ON SUBMAXIMAL EXERCISE METABOLISM AFTER DEPLETION OF MUSCLE GLYCOGEN

The effect of L-carnitine on energy metabolism at a high lipolytic flu x was studied. Nine healthy male subjects received L-carnitine (CARN) (3 g.d-1) for 7 d, or a placebo (CONT), both with Ca pentothenate. The treatment increased resting nitrogen excretion slightly (+ 15 %, P < 0.02). After an overnight fast, the subjects were submitted successive ly to 20 min bicycle exercise at 43 +/- 2 (SEM) %VO2max, a glycogen de pletion routine involving high intensity bouts to exhaustion, 1-2 h of rest, again 20 min at the initial load, and finally 20 min at 57 +/- 3 %VO2max. After glycogen depletion, blood short-chain acylcarnitine c oncentrations increased 5 times as much in CARN as in CONT (P < 0.02). Fat oxidation estimated from respiratory gas exchange doubled after g lycogen depletion for the same exercise intensity. However, there were no treatment differences in nonprotein RQ, heart rate, perceived fati gue, and blood parameters. It is concluded that during submaximal exer cise after glycogen depletion (i.e., at a high lipid flux) substrate m etabolism is not influenced by L-carnitine supplementation.