Md. Vukovich et al., CARNITINE SUPPLEMENTATION - EFFECT ON MUSCLE CARNITINE AND GLYCOGEN-CONTENT DURING EXERCISE, Medicine and science in sports and exercise, 26(9), 1994, pp. 1122-1129
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.