Morning compared to afternoon school-based exercise on cognitive function in adolescents

Purpose: Adolescents may be less ready to learn in the mornings due to a propensity for waking up later. High-intensity interval exercise (HIIE) has been shown to acutely improve cognitive functioning in teenagers. This within-measures study explored whether the benefit of HIIE differs when delivered in the morning or afternoon. Methods: 37 teenagers (19 boys, 13.7±0.4 years) each completed 3 trials in school; morning HIIE (MORN), afternoon HIIE (AFTER) and a no-exercise control trial (CON). The HIIE involved 10x10 second sprints, interspersed by 50 seconds of walking. Cognitive function was assessed using a battery of computerised tasks four times over the course of the day. Results: Z scores for reaction time, but not proportion of correct responses, were improved 45 minutes post exercise in the MORN trial (P<0.01, d=0.47), and this improvement persisted until the third (P=0.04, d=0.34), but not final (P=0.93, d=0.01), time point. Global reaction time was not improved 45 minutes post exercise in the AFTER trial (P=0.17, d=0.20). Global reaction time was quicker 45 minutes post morning exercise compared to the same time point in CON (P=0.02, d=0.56) and AFTER (P=0.01, d=0.72). Conclusion: HIIE may be more effectual in improving cognitive functioning when delivered in the morning.