Morning versus evening exercise: Its effect on body composition and weight loss

This study will use a multi-armed, randomised controlled trial design, with a 12-week lifestyle intervention. Following recruitment and screening, participants will complete baseline assessments and will then be randomised into one of two intervention groups, or the waitlist Control group. The primary component of the intervention is exercise, incorporating both supervised and unsupervised sessions. The two intervention conditions will be given the same instructions and encouragement, and differ only by the dedicated time slot to complete exercise; that is, in the morning, or in the evening. During the 12-week intervention participants will be prescribed 250 minutes of moderate-vigorous exercise per week, as recommended by the ACSM (2011) to elicit clinically significant weight loss. There will be no caveats to restrict additional exercise outside of the intervention, however, participants must complete the minimum dose of exercise during their respective time frame, conducive to their group allocation. That is, the AMEx group must complete minimum of 250 minutes of exercise between 0600 – 0900 h, and the PMEx group must complete =250 minutes of exercise between 1600 – 1900 h. These time periods were chosen to coincide with diurnal hormone patterns, and for convenience based on when most people could accommodate exercise (i.e. before or after work) (Blonc et al., 2010; Maraki et al., 2005). The exercise programme will comprise both instructor-supervised and unsupervised individual exercise sessions. Participants will complete an initial four-week supervised exercise training phase, with 5 sessions per week of 50 minutes. Phase 1 will involve four weeks of supervised exercise training, with 5 sessions per week to meet the minimum dose. Phase 2 will be eight weeks in duration and will involve a combination of supervised and unsupervised exercise sessions, tapering the supervised sessions from four times per week to twice per week. Weeks 5-6: 4 supervised sessions, weeks 7-8: 3 supervised sessions, weeks 9-12: 2 supervised sessions. Supervised sessions will consist of brisk walking or running on a motor-driven treadmill for approximately 50 minutes, at a self-selected intensity. All sessions will include a 10-minute warm-up and a 10-minute cool-down/stretching period. RPE will be recorded using the 6- to 20-point Borg scale (Borg, 1985) at the end of warm-up, during the session and at the end of the session (before cool-down). Participants are free to undertake other aerobic activities of their choice during the unsupervised sessions. Both intervention groups will receive the same instructions during the exercise sessions, including verbal encouragement and equal motivation. All supervised exercise sessions will be performed in the exercise laboratory at the Univerity of Queensland. To assist individuals achieve weight loss, the secondary component of the intervention will involve several constituents of behaviour change, including 1. self-monitoring: Participants will record their behaviour using exercise diaries and HR monitors. The act of keeping daily records requires conscious thought about activity levels and serves as a reminder to exercise (Gleeson-Kreig, 2006). Additionally, participants will weight themselves weekly to promote weight loss and reduce the risk of weight regain (Burke et al., 2011; Racette et al., 2006). 2. goal setting: Participants will be taught goal-setting techniques during the first week of the intervention. Following their first supervised exercise session, participants will be familiarised with the S.M.A.R.T technique (Specific, Measurable, Attainable, Relevant and Timely) to ensure the goals will likely be attained. Participants will be provided with written guidelines explaining the SMART principles so they have something to refer back to throughout the intervention, and will be instructed to set weekly goals to increase their energy expenditure, (both the intensity and dose). During the supervised exercise sessions, participants will self-select their work rate and the caloric expenditure will be visible on the treadmill. 3. education: Participants will be given instructions, feedback and guidance about use of exercise equipment, exercise technique, and recognising cues for injury avoidance. Participants will also be provided with a booklet containing the Australian Dietary Guidelines and pictures to accurately measure food portion sizes prior to the start of the intervention. 4. encouragement and support: Data from participants HR monitors will be downloaded weekly. During this time, participants will be asked about their progress and any potential barriers to exercise will be identified and methods to help overcome them will be discussed. 5. Prompting: Participants will be sent email/text message reminders to attend their supervised exercise sessions. After their session, participants will be prompted to incorporate some active transport or active leisure time each week. During phase 2, participants will be reminded to complete the required dose of unsupervised exercise. All education, encouragement and motivation will be standardised across the intervention groups. Adherence to the intervention will be assessed by recording attendance to supervised sessions, self-reported exercise diaries and data downloaded from heart rate monitors.