Power of Choice on Autonomy, Motivation, Exercise Adherence, and Cardiorespiratory Fitness

Individuals randomized to MICT will be asked to engage in only MICT 5 times/week for 30 min/session at 60-70% of heart rate max, consistent with physical activity guidelines of 150 min/week of moderate activity. Individuals are asked to engage in only MICT exercise during the 4-week supervised and unsupervised exercise sessions. During the supervised exercise the intensity will be based on the heart rate (HR) monitors and psychophysiological responses of perceived exertion. The exercise training is paired with 30-50 minutes of behavioral counselling that is identical for all three interventions.

Individuals randomized to HIIT will be asked to engage in only HIIT 5 times/week for 4 weeks. HIIT consists of 5 repeated vigorous intervals of 1-min duration at 80-90% of heart rate max interspersed with 1-min recovery periods. A 3-min warm-up and 2-min cool-down are also included, for a total session duration of 15 minutes. This matches the guidelines of 75 min of vigorous exercise per week. During the supervised exercise sessions, intensity will be based on HR monitors and psychophysiological responses of perceived exertion. The exercise training is paired with 30-50 minutes of behavioral counselling that is identical for all three interventions.

Participants will first be familiarized with HIIT and MICT in a randomized, counter-balanced order during supervised sessions 1 and 2, and will subsequently self-select the exercise type for the supervised and unsupervised exercise sessions. The HIIT and MICT protocols will match to the parallel imposed conditions. During the supervised exercise, intensity will also be based on HR monitors and psychophysiological responses of perceived exertion. The exercise training is paired with 30-50 minutes of behavioral counselling that is identical for all three interventions.