Dietary carbohydrate and postexercise synthesis of proglycogen and macroglycogen in human skeletal muscle

Abstract

This study examined the role of carbohydrate (CHO) ingestion on the resynthesis of two pools of glycogen, proglycogen (PG) and macroglycogen (MG), in human skeletal muscle. Nine males completed an exhaustive glycogen depletion exercise bout at 70% maximal O2 consumption on two occasions. Subsequent 48-h dietary interventions consisted of either high (HC, 75% of energy intake) or low (LC, 32% of energy intake) CHO diets. Muscle biopsies were taken at exhaustion (EXH) and 4, 24, and 48 h later. The total muscle glycogen (Gt) at EXH for the HC and LC conditions was not significantly different, and the MG represented ∼12% of the Gt. From EXH to 4 h, there was an increase in the PG only for HC and no change in MG in either diet ( P < 0.05). From 4 to 24 h, the concentration of PG increased in both conditions ( P < 0.05). Between 24 and 48 h, in HC the majority of the increase in Gt was due to the MG pool ( P < 0.05). The MG and PG concentrations for HC were significantly greater than for LC at 24 and 48 h ( P < 0.05). At 48 h the MG represented 40% of the Gt for the HC diet and only 21% for the LC diet. There was no change in the net rates of synthesis of PG or MG over 48 h for LC ( P < 0.05). The net rate of PG synthesis from 0 to 4 h for HC was 16 ± 1.68 mmol glucosyl units ⋅ kg dry wt−1 ⋅ h−1, which was threefold greater than for LC ( P < 0.05). The net rate of PG synthesis decreased significantly from 4 to 24 h for HC, whereas the net rate of MG synthesis was not different over 48 h but was significantly greater than in LC ( P< 0.05). The two pools are synthesized at very different rates; both are sensitive to CHO, and the supercompensation associated with HC is due to a greater synthesis in the MG pool.