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1 Département de
Kinésiologie,
The purpose of this study was to compare the oxidation of
[13C]glucose (100 g)
ingested at rest or during exercise in six trained (TS) and six
sedentary (SS) male subjects. The oxidation of plasma glucose was also
computed from the volume of
13CO2
and
13C/12C
in plasma glucose to compute the oxidation rate of glucose released from the liver and from glycogen stores in periphery (mainly muscle glycogen stores during exercise). At rest, oxidative disposal of both
exogenous (8.3 ± 0.3 vs. 6.6 ± 0.8 g/h) and liver glucose (4.4 ± 0.5 vs. 2.6 ± 0.4 g/h) was higher in TS than in SS.
This could contribute to the better glucose tolerance observed at rest in TS. During exercise, for the same absolute workload [140 ± 5 W: TS = 47 ± 2.5; SS = 68 ± 3 %maximal oxygen uptake
(
O2 max)], [13C]glucose oxidation
was higher in TS than in SS (39.0 ± 2.6 vs. 33.6 ± 1.2 g/h),
whereas both liver glucose (16.8 ± 2.4 vs. 24.0 ± 1.8 g/h) and muscle glycogen oxidation (36.0 ± 3.0 vs. 51.0 ± 5.4 g/h) were lower. For the same relative workload (68 ± 3% O2 max:
TS = 3.13 ± 0.96; SS = 2.34 ± 0.60 l
O2/min), exogenous glucose
(44.4 ± 1.8 vs. 33.6 ± 1.2 g/h) and muscle glycogen oxidation (73.8 ± 7.2 vs. 51.0 ± 5.4 g/h) were higher in TS. However,
despite a higher energy expenditure in TS, liver glucose oxidation was similar in both groups (22.2 ± 3.0 vs. 24.0 ± 1.8 g/h). Thus exogenous glucose oxidation was selectively favored in TS
during exercise, reducing both liver glucose and muscle glycogen oxidation.
exogenous glucose; training; substrate utilization; insulin; stable isotopes
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