Postprandial improvement in insulin sensitivity after a single exercise session in adolescents with low aerobic fitness and physical activity

Abstract

The purpose of this study was to determine the acute and residual impact of a single exercise bout on meal glucose control in adolescents with habitually low physical activity. Twelve adolescents (seven females/five males, 14 ± 2 yr) completed three trials. One trial [No Exercise (No Ex)] was completed after refraining from vigorous activity for ≥ 3 d. On the other two trials, a 45-min aerobic exercise bout at 75% peak heart rate was performed either 17-h Prior Day Exercise (Prior Day Ex) trial or 1-h Same Day Exercise (Same Day Ex) trial before consuming the test meal (2803 kJ, 45/40/15% energy as carbohydrate/fat/protein, respectively). Compared to No Ex, insulin sensitivity (SI) (minimal model analysis) was increased by 45% (p < 0.03) and 78% (p < 0.01) on the Prior Day Ex and Same Day Ex trials, respectively. This improvement in glucose control was supported by corresponding reductions in the net area under the curve for glucose, insulin, and c-peptide, although there was no change in postprandial suppression of fatty acids. These results show that SI is improved with a single bout of moderate intensity exercise in adolescents with habitually low physical activity and that the residual beneficial effect of exercise lasts at least 17 h. This finding highlights the plasticity of exercise responses in youth and the importance of daily exercise for metabolic health.

Fig. 1.

Study protocol. Each of the three morning study trials began with a baseline rest phase (rest 1). The intravenous catheter was placed just prior to the first blood collection. Thereafter, all procedures followed the same time course for each trial while the participants rested quietly (rest 2). The primary difference among trials was whether exercise was performed prior to the meal (none for No Exercise), or the timing of the exercise in relation to the meal (exercise in the Prior Day Exercise trial was completed 16 h before rest 1 and 17 h before the start of the meal; exercise in the Same Day Ex trial was completed 40 min prior to the start of the meal). The meal was consumed within 5 min. Indirect calorimetry was performed for 30 min during rest 1 (shown as dashed lines to reflect slight timing difference among trials) and for 20 min at each time point during rest 2.

Fig. 2.

Post-meal responses in glucose, insulin, c-peptide and non-esterified fatty acids. Values shown as mean ± SEM for 12 children. *No Exercise (No Ex) > Prior Day Exercise (Prior Day Ex) and Same Day Ex trials; ^†Same Day Ex < (10 and 30 min) or > (120 and 180 min) No Ex trial; ^§Same Day Ex > Prior Day Ex trial, p < 0.05.

Fig. 3.

Upper row: minimal model indices of insulin sensitivity (SI) and basal and dynamic pancreatic beta-cell function (Phi). Lower row: Incremental AUC for glucose, insulin, c-peptide, and fatty acids during the post-meal period. Values shown as mean ± SEM for 12 children. *p < 0.05 vs. No Exercise; ^†p < 0.05 vs. Prior Day Exercise trial.

Fig. 4.

Post-meal responses in energy expenditure and fuel oxidation. Energy expenditure was increased throughout the post-meal period relative to baseline but did not differ among trials. Carbohydrate (CHO) oxidation increased above baseline from 60 to 180 min in the No Exercise (No Ex) and Prior Day Exercise (Prior Day Ex) trials but not the Same Day Ex trial. *No Ex > Same Day Ex; Prior Day Ex > Same Day Ex, p < 0.05.