EFFECT OF ENDURANCE EXERCISE TRAINING ON MUSCLE GLYCOGEN SUPERCOMPENSATION IN RATS

The purpose of this study was to test the hypothesis that the rate and extent of glycogen supercompensation in skeletal muscle are increased by Endurance exercise training. Rats were trained by using a 5-wk-lon g swimming program in which the duration of swimming was gradually inc reased to 6 h/day over 3 wk and then maintained at 6 h/day for an addi tional 2 wk. Glycogen repletion was measured in trained and untrained rats after a glycogen-depleting bout of exercise. The rats were given a rodent chow diet plus 5% sucrose in their drinking water ad libitum during the recovery period. There were remarkable differences in both the rates of glycogen accumulation and the glycogen concentrations att ained in the two groups. The concentration of glycogen in epitrochlear is muscle averaged 13.1 +/- 0.9 mg/g wet wt in the untrained group and 31.7 +/- 2.7 mg/g in the trained group (P < 0.001) 24 h after the exe rcise. This difference could not be explained by a training effect on glycogen synthase. The training induced similar to 50% increases in mu scle GLUT-4 glucose transporter protein and in hexokinase activity in epitrochlearis muscles. We conclude that endurance exercise training r esults in increases in both the rate and magnitude of muscle glycogen supercompensation in rats.