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1 Human Biology and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada N1G 2W1 and 2 Copenhagen Muscle Research Centre, Rigshospitalet, DK-2200 Copenhagen N, Denmark
We examined the net catabolism of two pools of
glycogen, proglycogen (PG) and macroglycogen (MG), in human skeletal
muscle during exercise. Male subjects (n = 21) were
assigned to one of three groups. Group 1 exercised 45 min at
70% maximal O2 uptake (
O2 max) and had muscle biopsies at
rest, 15 min, and 45 min. Group 2 exercised at 85%
O2 max to exhaustion (45.4 ± 3.4 min) and had biopsies at rest, 10 min, and exhaustion. Group
3 performed three 3-min bouts of exercise at 100%
O2 max separated by 6 min of rest.
Biopsies were taken at rest and after each bout. Group 1 had
small MG and PG net glycogenolysis rates (ranging from 3.8 ± 1.0 to 2.4 ± 0.6 mmol glucosyl
units · kg
1 · min
1)
that did not change over time. In group 2, the MG
glycogenolysis rate remained low and unchanged over time, whereas the
PG rate was initially elevated (11.3 ± 2.3 mmol glucosyl
units · kg
1 · min
1) and
declined (P
0.05) with time. During the first 10 min, PG
concentration ([PG]) declined (P
0.05), whereas MG
concentration ([MG]) did not. Similarly, in group 3, in
both the first and the second bouts of exercise [PG] declined
(P
0.05) and [MG] did not, although by the end of the
second exercise period the [MG] was lower (P
0.05) than
the rest level. The net catabolic rates for PG in the first two
exercises were 22.6 ± 6.8 and 21.8 ± 8.2 mmol glucosyl
units · kg
1 · min
1, whereas
the corresponding values for MG were 17.6 ± 6.0 and 10.8 ± 5.6. The MG pool appeared to be more resistant to mobilization, and,
when activated, its catabolism was inhibited more rapidly than that of
PG. This suggests that the metabolic regulation of the two
pools must be different.
glycogen; glycogen phosphorylase; carbohydrate; metabolic compartments; repeated exercise; intermittent exercise
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