Author(s): BRUGGISSER, F., INFANGER, D., HANSSEN, H., KNAIER, R., Institution: UNIVERSITY BASEL, Country: SWITZERLAND, Abstract-ID: 812

INTRODUCTION:
Impaired glycaemic control is a major risk factor for cardiovascular disease, the leading cause of death worldwide. Increasing physical activity is a key strategy to improve glycaemic control. The circadian system influences glucose metabolism, causing 24-hour fluctuations in plasma glucose with a peak later in the day. Metabolic responses may vary depending on the time of day during which exercise is performed. Evidence of diurnal variations in physical performance, combined with the timing of behaviours such as sleep and diet, suggests that the timing of exercise may influence adaptations and health outcomes. This study aimed to investigate the impact of exercise timing on glycaemic control and optimise metabolic health strategies.
METHODS:
Sixty non-diabetic adults (36% female, mean [standard deviation] age 68 [6] years, BMI 24.1 [2.7] kg/m²) participated in this double-blind, randomised controlled trial. Participants were assigned to exercise at 8:00, 12:00, 16:00 or 20:00 (E-08, E-12, E-16, E-20) for 12 weeks, performing two strength and one endurance session weekly. A two-hour oral glucose tolerance test was performed before and after the intervention following an overnight fast. Serum glucose was measured at fasting and 10, 20, 30, 60, 90 and 120 min after ingestion of 75g dextrose. Glucose response was quantified as area under the curve (AUC) using the trapezoidal method. Treatment effects over time were analysed using analysis of covariance with estimated marginal means, adjusted for sex, age, lean mass and fat mass. Effect sizes were standardised using baseline standard deviations.
RESULTS:
Fifty-two participants were analysed (E08: n=14, E-12: n=15, E-16: n=7, E-20: n=16), with most dropouts due to missing more than two serum glucose values. Exercise adherence was excellent with 93% of all sessions completed. AUC decreased more in the E-16 group than in the others, with effect sizes being E-08: -0.21 (-0.68 to 1.10), E-12: -0.29 (-0.56 to 1.15) and E-20: -0.30 (-1.15 to 0.54), all considered small. Negative effect sizes, indicating a reduction in AUC, are considered beneficial for metabolic health. However, there was considerable uncertainty about these effects. Comparisons between the remaining groups showed negligible effect sizes (< 0.10).
CONCLUSION:
The timing of exercise appears to influence metabolic adaptations, with different patterns observed between exercise groups. The results suggest that exercising at a time of day when glucose metabolism is less efficient (e.g. E-16) may lead to greater adaptations. However, the wide confidence intervals indicate considerable uncertainty in these results. Further research is needed to improve our understanding of the underlying metabolic mechanisms and to provide a scientific basis for integrating exercise timing into health and metabolic management strategies.