Postexercise muscle and liver glycogen metabolism in male and female rats

Male and female Wistar rats were run for 5 min at 1.7 mph at a 17% grade to determine whether a sex difference exists in the rate of glycogen resynthesis during recovery in fast-twitch red muscle, fast-twitch white muscle, and liver. Rats were killed at one of three time points: immediately after the exercise bout, and at 1 or 4 h later. Males had significantly higher resting muscle glycogen levels (P < 0.05). Exercise resulted in significant glycogen depletion in both sexes (P < 0.01). Males utilized ~50% more glycogen during the exercise bout than females (P < 0.05). During the food-restricted 4-h recovery period, muscle glycogen was repleted significantly during the 1st h (P < 0.05). Liver glycogen was not depleted as a result of the exercise bout, but fell during the first h of recovery (P < 0.05) and remained low during the subsequent 3 h. The greater glycogen utilization in red and white fast-twitch muscle during exercise by males could represent a true sex difference but could also be attributable in part to the males having performed more work as a result of 20% greater body mass. We conclude that 1) no sex difference was observed in the rates of muscle glycogen repletion after exercise or in liver glycogen metabolism during and after exercise, and 2) rapid postexercise muscle glycogen repletion occurred at a time of accelerated liver glycogen depletion.