© 2017 Informa UK Limited, trading as Taylor. &. Francis Group. The purpose of this study was to assess the acute effect of high-intensity interval exercise (HIIE) and moderate-intensity exercise (MIE) on glucose tolerance, insulin sensitivity and fat oxidation in young boys. Eleven boys (8.8 ± 0.8 y) completed three conditions: 1) HIIE; 2) work-matched MIE; and 3) rest (CON) followed by an oral glucose tolerance test (OGTT) to determine glucose tolerance and insulin sensitivity (Cederholm index). Fat oxidation was measured following the OGTT using indirect calorimetry. There was no effect for condition on plasma [glucose] and [insulin]. area under the curve (AUC) responses following the OGTT (P  >  0.09). However, there was a “trend” for a condition effect for insulin sensitivity with a small increase after HIIE (P = 0.04, ES = 0.28, 9.7%) and MIE (P = 0.07, ES = 0.21, 6.5%) compared to CON. There was an increase in fat oxidation AUC following HIIE (P = 0.008, ES = 0.79, 38.9%) compared to CON, but with no differences between MIE and CON and HIIE and MIE (P  >  0.13). In conclusion, 7- to 10-year-old boys may have limited scope to improve insulin sensitivity and glucose tolerance after a single bout of HIIE and MIE. However, fat oxidation is augmented after HIIE but not MIE.

This study examined the time course of adaptions in insulin sensitivity (IS) in adolescent boys after acute high-intensity interval exercise (HIIE) and moderate-intensity exercise (MIE). Eight boys (15.1±0.4 y) completed three 3-day experimental trials in a randomised order: 1) 8×1 min cycling at 90% peak power with 75 s recovery (HIIE); 2) cycling at 90% of gas exchange threshold for a duration to match work during HIIE (MIE); and 3) rest (CON). Plasma [glucose] and [insulin] were measured before (PRE-Ex), 24 and 48 h post (24 h-POST, 48 h-POST) in a fasted state, and 40 min (POST-Ex) and 24 h (24 h-POST) post in response to an oral glucose tolerance test (OGTT). IS was estimated using the Cederholm (OGTT) and HOMA (fasted) indices. There was no change to HOMA at 24 h or 48 h-POST (all P>0.05). IS from the OGTT was higher POST-EX for HIIE compared to CON (17.4%, P=0.010, ES=1.06), and a non-significant increase in IS after MIE compared to CON (9.0%, P=0.14, ES=0.59). At 24 h-POST, IS was higher following both HIIE and MIE compared to CON (HIIE: P=0.019, 13.2%, ES=0.88; MIE: 9.7%, P=0.024, ES=0.65). In conclusion, improvements to IS after a single bout of HIIE and MIE persist up to 24 h after exercise when assessed by OGTT.

Current physical activity guidelines for youth with type 1 diabetes (T1D) are poorly supported by empirical evidence and the optimal dose of physical activity to improve glycemic control is unknown. This case report documents the effect of acute high-intensity interval exercise (HIIE) and moderate-intensity exercise (MIE) on 24-h glycemic control in three adolescents with T1D using continuous glucose monitoring. Results highlight varied individual response to exercise across the participants. In two participants both MIE and HIIE resulted in a drop in blood glucose during exercise (-38 to -42% for MIE and -21-46% in HIIE) and in one participant both MIE and HIIE resulted in increased blood glucose (+19% and + 36%, respectively). Over the 24-h period average blood glucose was lower for all participants in the HIIE condition, and for two for the MIE condition, compared to no exercise. All three participants reported HIIE to be more enjoyable than MIE These data show both HIIE and MIE have the potential to improve short-term glycemic control in youth with T1D but HIIE was more enjoyable. Future work with a larger sample size is required to explore the potential for HIIE to improve health markers in youth with T1D.

© 2014 Sports Medicine Australia. Objectives: High-intensity interval exercise (HIIE) may offer a time efficient means to improve health outcomes compared to moderate-intensity exercise (MIE). This study examined the acute effect of HIIE compared to a work-matched bout of MIE on glucose tolerance, insulin sensitivity (IS), resting fat oxidation and exercise enjoyment in adolescent boys. Design: Within-measures design with counterbalanced experimental conditions. Methods: Nine boys (14.2 ± 0.4 years) completed three conditions on separate days in a counterbalanced order: (1) HIIE; (2) work matched MIE, both on a cycle ergometer; and (3) rest (CON). An oral glucose tolerance test (OGTT) was performed after exercise or rest and the area under curve (AUC) responses for plasma [glucose] and [insulin]. were calculated, and IS estimated (Cederholm index). Energy expenditure and fat oxidation were measured following the OGTT using indirect calorimetry. Exercise enjoyment was assessed using the Physical Activity Enjoyment Scale. Results: the incremental AUC (iAUC) for plasma [glucose] was reduced following both MIE (-23.9%, P= 0.013, effect size [ES]. = -0.64) and HIIE (-28.9%, P= 0.008, ES = -0.84) compared to CON. The iAUC for plasma [insulin] was lower for HIIE (-24.2%, P= 0.021, ES. = -0.71) and MIE (-29.1%, P= 0.012, ES = -0.79) compared to CON. IS increased by 11.2% after HIIE (P= 0.03, ES = 0.76) and 8.4% after MIE (P= 0.10, ES = 0.58). There was a trend for an increase in fat oxidation following HIIE (P= 0.097, ES. = 0.70). Both HIIE and MIE were rated as equally enjoyable (P >. 0.05, ES. <. 0.01). Conclusion: a single bout of time efficient HIIE is an effective alternative to MIE for improving glucose tolerance and IS in adolescent boys immediately after exercise.

High-intensity interval training (HIIT) improves traditional cardiovascular disease (CVD) risk factors in adolescents, but no study has identified the influence of HIIT on endothelial and autonomic function in this group. Thirteen 13- to 14-yr-old adolescents (6 girls) completed six HIIT sessions over 2 wk. Each training session consisted of eight to ten 1-min repetitions of cycling at 90% peak power interspersed with 75 s of unloaded cycling. Traditional (triglycerides, cholesterol, glucose, insulin, and blood pressure) and novel [flow-mediated dilation (FMD), heart rate variability (HRV)] CVD risk factors were assessed in a fasted and postprandial state before (PRE), 1 day after (POST-1D), and 3 days after (POST-3D) training. Aerobic fitness was determined PRE and POST-3D. Two weeks of HIIT had no effect on aerobic fitness or traditional CVD risk factors determined in the fasted or postprandial state (P > 0.15). Compared with PRE, fasted FMD was improved POST-1D [P = 0.003, effect size (ES) = 0.70] but not POST-3D (P = 0.32, ES = 0.22). Fasted FMD was greater POST-1D compared with POST-3D (P = 0.04, ES = 0.48). Compared with PRE, postprandial FMD was greater POST-1D (P < 0.001, ES = 1.01) and POST-3D (P = 0.01, ES = 0.60). Fasted HRV was greater POST-1D (P = 0.001, ES = 0.71) and POST-3D (P = 0.02, ES = 0.44). The test meal lowered HRV in all laboratory visits (P < 0.001, ES = 0.59), but there were no differences in postprandial HRV between visits (P > 0.32 for all). Two weeks of HIIT enhanced endothelial function and HRV without improvements in traditional CVD risk factors. However, most of this favorable adaptation was lost POST-3D, suggesting that regularly performing high-intensity exercise is needed to maintain these benefits.