Exercise training induces glycogen sparing during exercise by old rats

Abstract

Glycogen utilization during exercise appears to be related to muscle respiratory capacity. Since the decline in hindlimb muscle respiratory capacity that occurs in rats during old age is eliminated when young and old rats undergo an identical exercise training protocol, liver and gastrocnemius glycogen concentrations were determined in identically trained young and old Fischer 344 rats at rest and immediately after a 30-min run requiring approximately 75% of maximal O2 consumption. These values were also compared with untrained age-matched control animals. The animals, which were 10 or 24 mo old after 6 mo of training, were fasted for 24 h before they were killed. Resting gastrocnemius glycogen did not differ among the groups. After 30 min of running, gastrocnemius glycogen was lower in the untrained than the trained groups and was not different between the trained groups. Resting liver glycogen was lower in the old trained group than the untrained groups but not statistically different from the young trained group. The postrun liver glycogen did not differ among the groups. Estimated gastrocnemius and liver glycogen utilization during exercise was decreased in both trained groups compared with untrained age-matched controls. These results indicate that the training-induced glycogen sparing during exercise of the same relative intensity was not diminished with age in identically trained young and old rats.