No Effect of Exercise Timing on Daily Glycaemia Despite Shifts in Acute Glucose Dynamics in Participants with Normal Glucose Tolerance: A Randomised Crossover Trial

Exercise is a well-established modulator of glucose regulation, but whether the time of day it is performed matters for healthy, free-living adults remains unresolved. In a randomised crossover trial, 29 healthy adults completed a single 30-minute bout of moderate-intensity exercise in the morning (07:00-10:00) and in the evening (16:00-19:00), with continuous glucose monitoring and wrist-worn activity tracking used to capture responses over an 8-day free-living protocol. Evening exercise produced a significantly greater acute reduction in blood glucose (P < 0.001) compared to morning exercise, but this did not translate into consistent differences in overall daily mean glycaemic exposure, whether measured over the calendar day or over a window aligned with exercise onset. Evening exercise was linked to greater within-day glycaemic variability than morning exercise, with the clearest evidence coming from the circadian-aligned analysis (day x timing interaction, SD: P = 0.00939; CV: P = 0.00766). Appetite rose after exercise in both conditions, with no difference by time of day. Taken together, these results show that exercise timing does not change how much glucose exposure a healthy adult accumulates over a day, but it does change the shape of the glucose response around the exercise bout itself, a distinction only visible when glucose is examined at a finer temporal resolution than daily averages allow.