Pro- and macroglycogenolysis during repeated exercise: roles of glycogen content and phosphorylase activation

This study examined the relationship between preexercise muscle glycogen co ntent and glycogen utilization in two physiological pools, pro- (PG) and ma croglycogen (MG). Male:subjects (n = 6) completed an exercise and dietary p rotocol before the experiment that resulted in one leg with high: glycogen (HL) and one with low glycogen (LL). Preexercise PG levels were 312 +/- 29 and 208 +/- 31 glucosyl units/kg dry wt (dw) (P less than or equal to 0.05) in the HL and LL, respectively, and the corresponding values for MG were 1 25 +/- 37 and 89 +/- 43 mmol glucosyl units/kg dw (P less than or equal to 0.05). Subjects then performed two 90-s exercise bouts at 130% maximal oxyg en uptake separated by a 10-min rest period. Biopsies were obtained at rest and after each exercise bout. Preexercise glycogen concentration was corre lated to net glycogenolysis for both PG and MG for bout 1 and bouts 1 and 2 (r less than or equal to 0.60). In bout I, there was no difference in the rate of PG or MG catabolism between HL and LL despite a 26% increase (P les s than or equal to 0.05) in glycogen phosphorylase transformation (phos a % ) in the HL. In the second bout, more PG was catabolized in the HL vs. LL ( 38 +/- 9 vs. 9 +/- 6 mmol glucosyl units kg dw-l min-l) (P less than or equ al to 0.05) with no difference between legs in phos a %. phos a % was incre ased in HL vs. LL but does not necessarily increase glycogenolysis in eithe r PG or MG. Despite both legs performing the same exercise and having ident ical metabolic demands, the HL catabolized 2.3 (P less than or equal to 0.0 5) times more PG and 1.5 (P less than or equal to 0.05) times more MG vs. L L in bents 1 and,2, indicating that preexercise glycogen concentration is a regulator of glycogenolysis.