The goal of this clinical trial was to assess the effects of morning vs. evening high-intensity interval exercise on the magnitude of the morning blood pressure surge in young healthy adults. The main questions it aimed to answer were:

• Does the timing of high-intensity interval exercise modulate the magnitude of the morning blood pressure surge?
• Do sex differences exist?

Participants came in and completed a bout of high-intensity interval exercise in the morning (8-10 am) and evening (5-7 pm) as well as a no exercise control, and ambulatory blood pressure was assessed for 24 hours afterwards.

Introductory Visit:

Participants came in for 4 visits. The first visit was an introductory visit where chronotype, eligibility for exercise, and anthropometrics were measured. This was followed by a maximal incremental exercise test to determine aerobic capacity (i.e., V̇O2peak) on a cycle ergometer, and instrumentation of an ambulatory blood pressure monitor for familiarization during daily activities and sleep.

Intervention Visits:

Three intervention visits (control, morning exercise, and evening exercise) were completed. The order was randomized using and each visit was separated by a minimum of 36 hours. Each intervention visit began by obtaining the participant's resting blood pressure and heart rate and ended with the instrumentation of the ambulatory blood pressure monitor. No exercise was performed during the control visit. The morning exercise visit included a bout of high-intensity interval exercise between 8-10 am and the evening exercise visit included a bout of high-intensity interval exercise between 5-7 pm. The high-intensity interval exercise protocol consisted of a light intensity, 3-minute warm-up at 15% peak power followed by ten 1-minute work intervals at 80% of peak power, with each interval separated by 1-minute rest intervals at 15% peak power. A 3-minute cool down was performed at 15% peak power.

Inclusion:

• Between 18-50 years of age.
• No history of known disease.
• None smokers.
• No use of chronic medications other than oral contraceptives.

Exclusion:

• <18 years of age.
• >50 years of age.
• Cardiovascular disease.
• Metabolic disease.
• History of smoking (within the past 3 months).
• Chronic medications (other than oral contraceptives).

Individual participant data that underlie the results reported in this article, after deidentification (text, tables, figures, and appendices).

After publication; unending.

Investigators whose proposed use of the data has been approved by an independent review committee ("learned intermediary") identified for this purpose.