Training-induced alterations of glucose flux in men.

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Abstract
Friedlander, Anne L., Gretchen A. Casazza, Michael A. Horning, Melvin J. Huie, and George A. Brooks. Training-induced alterations of glucose flux in men. J. Appl. Physiol. 82(4): 1360–1369, 1997.—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 (V˙o 2 peak)] 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 increasedV˙o 2 peak by 9.4 ± 1.4%. Pretraining, the intensity effect on glucose kinetics was evident with rates of appearance (Ra; 5.84 ± 0.23 vs. 4.73 ± 0.19 mg ⋅ kg−1 ⋅ min−1), disappearance (Rd; 5.78 ± 0.19 vs. 4.73 ± 0.19 mg ⋅ kg−1 ⋅ min−1), oxidation (Rox; 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%V˙o 2 peak trial. When Rd was expressed as a percentage of total energy expended per minute (Rd E), there was no difference between the 45 and 65% intensities. Training did reduce Ra (4.63 ± 0.25), Rd (4.65 ± 0.24), Rox (3.77 ± 0.43), and Rd E (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, Ra, Rd, and Rd E were not different, although Rox 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.