M. Hargreaves et al., INFLUENCE OF MUSCLE GLYCOGEN ON GLYCOGENOLYSIS AND GLUCOSE-UPTAKE DURING EXERCISE IN HUMANS, Journal of applied physiology, 78(1), 1995, pp. 288-292
To examine the effects of alterations in preexercise muscle glycogen a
vailability on glycogenolysis and glucose uptake during exercise, 12 a
ctive but untrained men [22.8 +/- 1.6 (SE) yr, 71.7 +/- 2.0 kg, peak p
ulmonary oxygen uptake 3.85 +/- 0.16 l/min] were studied during 40 min
of cycle ergometer exercise at 65-70% peak pulmonary oxygen uptake on
two separate occasions, at least 1 wk apart. Preexercise muscle glyco
gen concentrations were manipulated by having the subjects perform gly
cogen-lowering exercise either 24 or 48 h before a trial, in combinati
on with either high or low dietary carbohydrate intake. In series I (n
= 7), increasing muscle glycogen from 90.3 +/- 6.0 to 124.7 +/- 10.8
mmol/kg wet wt increased muscle glycogenolysis during exercise (62.7 /- 7.9 vs. 49.1 +/- 6.6 mmol/kg; P < 0.05). Similarly, in series 2 (n
= 5) when muscle glycogen was reduced from 96.2 +/- 6.6 to 53.7 +/- 6.
0 mmol/kg, glycogen utilization during exercise was reduced from 51.8
+/- 4.6 to 28.3 +/- 3.8 mmol/kg (P < 0.05). The altered muscle glycoge
n utilization was associated with alterations in carbohydrate oxidatio
n during exercise, without effect on tracer ([H-3]glucose)-determined
glucose uptake. These results indicate that preexercise muscle glycoge
n availability influences muscle glycogenolysis, but not glucose uptak
e, during exercise.