Training-induced alterations of glucose flux in men

Abstract

We examined the hypothesis that glucose flux was directly related to relative exercise intensity both before and after a 10-wk cycle ergometer training program in 19 healthy male subjects. Two pretraining trials [45 and 65% of peak O2 consumption (V̇O(2peak))] and two posttraining trials (same absolute and relative intensities as 65% pretraining) were performed for 90 min of rest and 1 h of cycling exercise. After training, subjects increased V̇O(2peak) by 9.4 ± 1.4%. Pretraining, the intensity effect on glucose kinetics was evident with rates of appearance (R(a); 5.84 ± 0.23 vs. 4.73 ± 0.19 mg · kg-1 · min-1), disappearance (R(d); 5.78 ± 0.19 vs. 4.73 ± 0.19 mg · kg-1 · min-1), oxidation R(ox); 5.36 ± 0.15 vs. 3.41 ± 0.23 mg · kg-1 · min-1), and metabolic clearance (7.03 ± 0.56 vs. 5.20 ± 0.28 ml · kg-1 · min-1) of glucose being significantly greater (P ≤ 0.05) in the 65% than the 45% V̇O(2peak) trial. When R(d) was expressed as a percentage of total energy expended per minute (R(dE)), there was no difference between the 45 and 65% intensities. Training did reduce R(a) (4.63 ± 0.25), R(d) (4.65 ± 0.24), R(ox) (3.77 ± 0.43), and R(dE) (15.30 ± 0.40 to 12.85 ± 0.81) when subjects were tested at the same absolute workload (P ≤ 0.05). However, when they were tested at the same relative workload, R(a), R(d), and R(dE) were not different, although R(ox) was lower posttraining (5.36 ± 0.15 vs. 4.41 ± 0.42, P ≤ 0.05). These results show 1) glucose use is directly related to exercise intensity; 2) training decreases glucose flux for a given power output; 3) when expressed as relative exercise intensity, training does not affect the magnitude of blood glucose use during exercise; 4) training alters the pathways of glucose disposal.