Glycogen resynthesis in leg muscles of rats during exercise

This study was undertaken to determine whether glycogen resynthesis can occur in glycogen-depleted muscles in response to glucose feeding during prolonged exercise. Rats were exercised for 40 min with a treadmill running program designed to deplete muscle glycogen. One group was studied immediately after the glycogen-depletion exercise. A second group was given 1 g glucose by stomach tube and exercised for an additional 90 min at a running speed of 22 m/min on a treadmill set at an 8 degree incline; they were given additional 1-g glucose feedings after 30 and 60 min of running. The initial 40-min run resulted in liver glycogen depletion, large decreases in plasma glucose and insulin concentrations, and a marked lowering of muscle glycogen. The glucose feedings resulted in greater than twofold increases in the concentrations of glucose and insulin in plasma, and of glycogen in leg muscles, during the 90 min of running. No repletion of liver glycogen occurred. These results provide evidence that glycogen resynthesis can occur in glycogen-depleted muscle despite continued moderate intensity exercise if sufficient glucose is made available.