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.
Alex’s Notes: Previous research in young adults has demonstrated the efficiency of high-intensity interval exercise (HIIE) to improve insulin sensitivity, but no research has yet to compare HIIE to steady state cardio (moderate intensity exercise: MIE) in adolescents. In the current study, nine pubertal boys (14 years old) were recruited from a local school to undergo four laboratory testing sessions on a cycle ergometer, separated by one week. The first session was used for body composition and cardiorespiratory fitness assessment. For sessions 2-4, the boys arrived at the lab after a 12 hour overnight fast to have resting metabolic rate (RMR), fasting glucose, and fasting insulin determined. Afterwards, they randomly completed one of three conditions:
- HIIE à 3 minute warmup à 8 bouts of 60 sec @ 90% peak power separated by 75 seconds recovery @ warmup intensity à 3 minute cool down
- MIE à continuous cycling at 90% VO2GET for duration calorically matched to HIIE
- Control à nothing
Ten minutes after each session the boys completed an oral glucose tolerance test and had RMR, glucose, and insulin testing for up to three hours afterwards. As would be expected, HIIE was significantly shorter in duration, lasting 22.8 minutes compared to 28.9 minutes of MIE. Power output and cardiorespiratory work were also significantly greater in the HIIE condition.
Overall, both HIIE and MIE had a significantly lower glucose response and a trend for a reduction in the insulin response compared to the control condition, with no significant differences between them. However, HIIE significantly increased insulin sensitivity by 11.2% compared to the control whereas there was only a trend for MIE to increase insulin sensitivity by 8.4%. Moreover, while RMR was unchanged in any condition, there was a trend for increased fat oxidation following HIIE compared to the control.
The differences between HIIE and MIE are trivial, which makes having the children do the method they prefer more prudent when designing exercise prescriptions. That said, HIIE does appear to have a small advantage in terms of insulin sensitivity and fat oxidation, although the latter has recently been shown to have little significance in the long-term.