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Department of Human Biology and Nutritional Sciences, University of Guelph, Guelph, Ontario N1G 2W1; and Department of Medicine and Kinesiology, McMaster University, Hamilton, Ontario, Canada L8N 3Z5
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.
glycogenin; recovery; acid-soluble and acid-insoluble glycogen; glycogen synthase; supercompensation; carbohydrate loading
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