Targeting Diurnal Exercise Timing to Increase Exercise Levels Among Adults With Obesity: A Randomized, Crossover Pilot

Performing at least 150 minutes of moderate intensity physical activity per week is associated with many health improvements. Some research suggests that people who exercise at the same time day-to-day perform more physical activity than those who exercise at variable times day-to-day, but it is not yet known if asking people to exercise at the same time day-to-day is helpful for becoming more active and whether there is a specific time of day (e.g., morning vs. evening) that is most helpful. Importantly, it is also not yet known whether people are able and willing to exercise at a specific time day-to-day. This study thus seeks to learn more about how feasible, acceptable, and helpful it is to exercise at an assigned time.

The study will last for 4 months total. Interested participants will be asked to attend an orientation visit at the research center to learn more about the study and will wear a physical activity monitor for 1 week to verify eligibility. Participants who enroll in the study will then complete a 45-minute session with study staff (in person or via videoconferencing) to learn strategies for safely increasing physical and will be asked to walk at a moderate intensity for at least 15 consecutive minutes every day during three, 3-week periods (9 weeks total). Each participant will be asked to perform this walking in the morning (5:00-10:00 AM) for one of the 3-week periods, in the evening (5:00-10:00 PM) for one of the 3-week periods, and at a time of their choice for one of the 3-week periods. Between each 3-week period with a daily exercise goal, there will be a 2-week break period with no exercise goal. Participants will be asked to wear a physical activity sensor on an elastic band around their waist during all waking hours for the full study duration to monitor their physical activity levels. They will also be emailed a survey about their physical activity each night during each of the 3-week exercise periods. Participants will receive a weekly email each week to provide support and encouragement for increasing their physical activity, and to report on how many days they wore the physical activity sensor. Lastly, participants will complete a visit at the research center at the end of the study to complete questionnaires about their experiences.