Small Steps for Big Changes

Overview

Exercise is a proven strategy for preventing type 2 diabetes. Traditionally individuals have been prescribed moderate-intensity continuous aerobic exercise but adherence to this standard exercise program is dismal. High-intensity interval training (HIIT) is a novel form of exercise that involves brief, repeated bursts of vigorous exercise separated by periods of recovery. HIIT elicits many favourable cardiometabolic adaptations that are similar to traditional exercise but does so with a lower amount of exercise and in substantially less time than moderate-intensity continuous exercise. Therefore, HIIT has been touted as a "time-efficient" exercise strategy for improving health. Whether overweight individuals at risk for pre diabetes will show greater adherence to HIIT than moderate-intensity continuous exercise over the long-term (12-months) has not been tested. Because exercise adherence requires complex self-regulation, interventions designed to improve adherence should include a behavioural component. The investigators will assess adherence to HIIT and moderate-intensity continuous exercise over 12 months following a short-term (2 week) intervention of either HIIT or moderate-intensity continuous exercise. Both conditions will include a self-regulatory component targeted to increase participants' confidence to engage in regular, independent exercise. The results will help determine whether HIIT is a more feasible option for promoting exercise adherence for pre diabetes prevention than the traditional moderate-intensity continuous exercise. The investigators hypothesize that a) over the 12 months follow-up subjects randomized to the HIIT will be more likely to adhere when compared to moderate-intensity continuous exercise, b) over the 12 months follow-up subjects randomized to HIIT will have higher rates of adherence and levels of total physical activity, c) greater increases in self-regulation (including goal setting, self-monitoring, and self-regulatory efficacy) following HIIT will mediate higher rates of adherence, d) 10-days of HIIT and moderate-intensity continuous exercise will improve cardiorespiratory fitness, increase insulin sensitivity, reduce circulating inflammatory markers, and improve glucose control and e) Improvements in cardiometabolic health factors will be greater following HIIT compared to moderate-intensity continuous exercise.

Eligible participants will be randomized to the HIIT or moderate-intensity continuous exercise conditions. Each condition will involve a two-week supervised exercise period consisting of ten sessions. Exercise prescriptions for each condition will be progressive in nature over the two week supervised period and will be matched for external work. Specifically, individuals randomized to HIIT will begin with four intervals lasting 1-minute each at \~85-90% peak oxygen uptake \[VO2peak\] and increased to 10 X 1-min intervals by day 10. Individuals randomized to moderate-intensity exercise condition will begin with 20 minutes of continuous activity at \~55-60% V02peak and gradually increase the duration to 50 minutes by day 10. Participants will self-select exercise modality (walking outdoors, elliptical machine, treadmill walking, or stationary cycling). One trainer will supervise participants during the 2-week training program. Participants will complete 3 of the 10 training days (day 4, 7 and 9) at home unsupervised. Participants will wear a heart rate monitor during each exercise session (supervised and unsupervised) to monitor exercise intensity and ensure compliance. In addition, participants will record their exercise bouts in a logbook on both lab and home training days. Participants in both conditions received 10 minutes of behavioural counseling each day they trained in the lab (for a total of 70 minutes). Following the supervised training, participants will be instructed to maintain HIIT or moderate-intensity continuous exercise three days per week independently. Specifically, individuals randomized to HIIT will be prescribed three exercise sessions per week involving 10 X 1-minute intervals at \~85-90% VO2peak, while participants randomized to moderate-intensity continuous exercise will be prescribed three session per week of 50-minute continuous exercise at \~55-60% VO2peak. Training logs will be provided and participants will be instructed to estimate exercise intensity based on physiological cues taught during supervised training days.