The effect of morning versus evening aerobic exercise on 24-hour ambulatory blood pressure

Aerobic exercise is a well-established intervention for blood pressure (BP) management; however, the influence of exercise timing on 24-hour ambulatory blood pressure (ABP) and related cardiovascular outcomes remains unclear. This study investigates whether morning or evening aerobic exercise elicits differential effects on 24-hour ABP, including systolic and diastolic BP, mean blood pressure (MBP), and pulse pressure (PP), nocturnal dipping patterns, sleep quality, and heart rate variability (HRV) in otherwise healthy, young adults. A randomized crossover design was used in which 13 participants completed both morning and evening 45-minute aerobic exercise sessions. ABP monitoring and actigraphy were used to assess 24-hour BP patterns, sleep variables such as total sleep time, sleep onset latency, wakefulness after sleep onset, and sleep efficiency, and HRV following three conditions: baseline (control), morning exercise, and evening exercise. Repeated-measures one-way ANOVAs and mixed effects models were used to analyze outcomes. Both morning and evening exercise caused a similar magnitude of post-exercise hypertension at 1-h post-exercise. However, no statistically significant differences were observed in systolic BP, diastolic BP, MBP, or PP dipping between morning and evening exercise conditions. Heart rate dipped more following morning than evening exercise (p = 0.03). Sleep outcomes, including total sleep time and sleep efficiency, did not differ significantly across conditions (all p > 0.04). HRV analysis revealed no significant changes during the nocturnal period or during the AM surge, defined as the hour immediately following wake up. Overall, while aerobic exercise timing did not significantly affect 24-hour BP or HRV metrics in this cohort, morning exercise may increase nocturnal heart rate dipping and both morning and evening exercise elicited post-exercise hypotension observable for ~1 h. These findings suggest that timing of aerobic exercise may have subtle physiological effects that warrant further investigation in larger samples and other populations (e.g., those with hypertension or disrupted sleep) in whom optimization of non-pharmacological strategies for BP management is important.