Training-induced alterations of carbohydrate metabolism in women: Women respond differently from men

Abstract

We examined the hypothesis that glucose flux was directly related to relative exercise intensity both before and after a 12-wk cycle ergometer training program [5 days/wk, 1-h duration, 75% peak O2 consumption (V̇O(2peak))] in healthy female subjects (n = 17; age 23.8 ± 2.0 yr). Two pretraining trials (45 and 65% of V̇O(2peak)) and two posttraining trials [same absolute workload (65% of old V̇O(2peak)) and same relative workload (65% of new V̇O(2peak))] were performed on nine subjects by using a primed- continuous infusion of [1-13C]- and [6,6-2H]glucose. Eight additional subjects were studied by using [6,6-2H]glucose. Subjects were studied postabsorption for 90 min of rest and 1 h of cycling exercise. After training, subjects increased V̇O(2peak) by 25.2 ± 2.4%. Pretraining, the intensity effect on glucose kinetics was evident between 45 and 65% of V̇o(2peak) with rates of appearance (R(a): 4.52 ± 0.25 vs. 5.53 ± 0.33 mg · kg-1 · min-1), disappearance (R(d): 4.46 ± 0.25 vs. 5.54 ± 0.33 mg · kg-1 · min-1), and oxidation (R(ox): 2.45 ± 0.16 vs. 4.35 ± 0.26 mg · kg-1 · min-1) of glucose being significantly greater (P ≤ 0.05) in the 65% than in the 45% trial. Training reduced R(a) (4.7 ± 0.30 mg · kg-1 · min-1), R(d) (4.69 ± 0.20 mg · kg-1 · min-1), and R(ox) (3.54 ± 0.50 mg · kg-1 · min-1) at the same absolute workload (P ≤ 0.05). When subjects were tested at the same relative workload, R(a), R(d), and R(ox) were not significantly different after training. However, at both workloads after training, there was a significant decrease in total carbohydrate oxidation as determined by the respiratory exchange ratio. These results show the following in young women: 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 flux during exercise; but 4) training does reduce total carbohydrate oxidation.