Postprandial glucose responses to standardised meals consumed after moderate- and high-intensity exercise bouts across standard school days in healthy adolescents

Exercise-induced moderation of postprandial glycaemia in adolescents is unclear and has not been examined under free-living conditions. We assessed the effect of moderate-intensity exercise (MIE) and high-intensity intermittent exercise (HIIE) bouts on subsequent postprandial glycaemic responses across three standard school days. Fourteen healthy adolescents (13 ± 1 years) completed three conditions in the following order across consecutive days: MIE, 30-min continuous brisk walking; CON, no-exercise control; HIIE, 30-min of 10 × 30-s sprints interspersed with 2.5-min brisk walking bouts. Participants consumed three standardised meals (breakfast, lunch and dinner) at standardised times. Interstitial glucose, energy intake, sedentary time and physical activity were assessed under free-living conditions. Linear mixed models compared glucose outcomes between conditions, and Cohen’s d effect sizes were calculated. Although non-significant, the reduction in post-breakfast glucose iAUC was moderate for MIE (-0.24 mmol·L-1; P = 0.59; d = 0.77) and large for HIIE (-0.26 mmol·L-1; P = 0.44; d = 0.86) compared with CON. Non-significant, moderate (0.37 mmol·L-1; P = 0.22; d = 0.70) and large (0.42 mmol·L-1; P = 0.20; d = 0.81) increases in post-lunch glucose iAUC were observed for MIE and HIIE compared with CON. Nevertheless, the 24-h mean glucose was stable at ~5.4 mmol·L-1 across conditions. The glycaemic variability indices calculated over 24-h after the onset of exercise for each condition including standard deviation (P = 0.59) and mean amplitude of glycaemic excursion (P = 0.82) were not different between conditions. Thirty-minute bouts of MIE and HIIE did not change postprandial glycaemia or 24-h glycaemic variability significantly in the small sample of healthy adolescents. However, the moderate and large effect sizes suggest both MIE and HIIE reduced breakfast glucose iAUC compared with CON, yet led to increases in post-lunch iAUC in the two exercise conditions. The mismatch between the probability values and effect sizes was a consequence of our COVID-reduced sample. The ramifications of these exercise effects are unclear and need to be confirmed in a larger sample of adolescents.