The effects of morning versus evening high-intensity interval exercise on the magnitude of the morning blood pressure surge.

Blood pressure (BP) follows a circadian rhythm, dipping during sleep and surging in the morning. A larger morning BP surge is an independent predictor of cardiovascular events. Acute exercise can produce sustained periods of post-exercise hypotension that last up to 24 h; however, the timing of exercise (morning vs. evening) may influence this response. Whether the timing of exercise influences the morning BP surge remains unknown. The current study investigated the effects of a bout of high-intensity interval exercise (HIIE) performed in the morning versus evening on the magnitude of the morning BP surge in young healthy adults. Twenty-six young, otherwise healthy adults (23 ± 4 years; 15 females) completed a randomized crossover trial where, on different days, they completed a no exercise control visit or performed either morning (0800-1000 h) or evening (1700-1900 h) HIIE. Following each visit, ambulatory BP was assessed in 30 min intervals for 24 hrs. HIIE at either time did not alter the magnitude of the morning BP surge compared to control values (control: 22 ± 5 mmHg; morning exercise: 20 ± 8 mmHg; evening exercise: 22 ± 10 mmHg,  = 0.40) or when grouped separately by sex (visit × sex  = 0.42). A positive correlation existed between Morningness-Eveningness Questionnaire score and the change in nighttime BP following both exercise times (both  = 0.42 and  = 0.04). These findings suggest that HIIE does not attenuate the morning BP surge in young healthy adults and that chronotype can predict nighttime BP responses following HIIE, irrespective of exercise time of day. This study was registered on ClinicalTrials.gov (NCT06702930).