The impact of exercise timing (morning vs. evening) on the circadian metabolic systems disrupted in the face of a high fat diet in middle-aged overweight men.

All subjects will eat a high fat diet for 11 days. On day 6 of the high fat diet, subjects in arm 1 and arm 2 will commence the first of five daily exercise sessions finishing on day 10. Subjects in Arm 1 will compete exercise at 7 AM and subjects in Arm 2 at 6 PM. Overview of design: Twenty-four sedentary males, body mass index (BMI): 27-35 kg/m2), will be included in a randomised (1:1:1), parallel groups design. There will be two exercise groups (one group exercising in the morning and one in the evening), and a control group. Materials: Participants will receive a participant information letter outlining study procedures and a handbook to log physical activity and sleep during the intervention and a daily food checklist. Procedures: Experimental conditions will take place at the Exercise Science facilities within the Daniel Mannix Building at Australian Catholic University. Participants will attend the laboratory on a minimum of 6 days (if allocated to the control group) or 11 days (if allocated to training), as detailed below. Visit 1: Forms, Resting Metabolic Rate, Dual-Energy X-Ray Absorptiometry (DXA), blood pressure measurements, anthropometry measurements, instructions to complete a three-day food record, exercise pre-screening questionnaire, peak oxygen uptake test (VO2peak). Visit 2, 2-7 days after visit 1: Continuous glucose monitor inserted, physical activity monitors put on, and food pick-up Visit 3 and 4 (morning and evening visits for both visits): Muscle biopsies and blood collection, blood pressure measurements, food pick-up. Visit 3 will be the day after visit 2. Visit 4 will be 5 days after visit 3. Visit 5-9 (only for participants allocated to training): Exercise training sessions, either in the morning or in the evening, depending on group allocation. All sessions will be conducted on a stationary cycle ergometer and supervised by an exercise physiologist. These visits will be on the five consecutive days after visit 4. Visit 5 (for participants allocated to control, 6 days after visit 4) or Visit 10 (for participants allocated to training, the day following visit 9). Morning and evening visit: muscle biopsies and blood collection, blood pressure measurements. Visit 6 (for participants allocated to control, 2 days after visit 5) or Visit 11 (for participants allocated to training, 2 days after visit 10): DXA scan, VO2peak, blood pressure measurement. Description of study procedures: Resting Metabolic Rate (RMR): Participants will lie down in a quiet, dim-lit room for 25 min where RMR will be measured using an automated gas analyser. A hood (clear) will be placed over the participants head and connected to the gas analyser. The 25 minutes includes a 10 minute rest period, followed by a 15 minute period of data collection. DXA: participants will undergo a whole body DXA scan. Participants will lay supine on the scanning bed for the duration of the 15 minute scan. There will be one to two scans depending on the body shape of the participant. The machine uses small doses (<1% of the yearly radiation dose) of radiation to estimate tissue density. The total effective dose of radiation has been calculated for this machine and the scans for this study by a Medical Physicist. This test requires the participant be fasted with no food, fluid or exercise/activity prior to the test. Light clothing with no metal items (i.e. zips, domes, clips, underwire etc.) should be worn (gowns are available if need be) and all jewellery must be removed. All measures will be taken by trained researchers who hold radiation licences with Victorian Government and comply to the Code of Practice set out by the Australian Radiation Protection and Nuclear Safety Agency. Blood pressure: blood pressure (BP) will be measured via an automated BP machine. Three measures will be taken, a minimum of 1 minute apart. Each measure is approximately 3 minutes in duration. The participant will have a cuff applied to the upper portion of the arm. This will inflate and tighten around the arm and then slowly release. Three-day dietary record: Participants will be given a three day diet record to complete. Continuous blood glucose monitoring (CGM): participants will be required to wear the minimally invasive Medtronic iPro2 blood glucose monitoring system from visit 2 and until visit 6/11. The monitor is the size of a 50 cent piece and the associated sensor inserted rather painlessly into the subcutaneous tissue of the lower back. The iPro2 will be worn continuously throughout the experimental conditions (16 days). Physical activity and sleep monitors: to assess physical activity and sleep, participants will be fitted with an inclinometer (ActivPAL3TM) worn on the thigh, an ActiGraph accelerometer worn around the waist, and a SenseWear armband worn on the triceps muscle, to be worn continuously throughout the experiment.. Blood sampling: samples will be collected via a venipuncture into the antecubital vein. A total of 36 mL will be collected each of these days, in total 108 mL from each participant. Muscle biopsy sampling: skeletal muscle biopsy samples will be obtained from the outer thigh (vastus lateralis) at 7:30 AM and 7:30 PM on three separate days throughout the experimental conditions. The muscle biopsy will be taken by Dr Andrew Garnham. Six muscle biopsies will be obtained from each participant in total. Exercise: On the first, third, and fifth visit participants will do 10 x 1 min cycling at 85% peak power output (PPO) with one min rest between work intervals at low intensity. The second session and fourth condition will be continuous moderate-intensity cycling for 40 min at 65% PPO (visit 4) and for 60 min at 60% PPO (visit 6). Dietary control: During the supervised feeding protocol our accredited research dietitian will create meal plans to provide participants with all meals and snacks. The diet will be a high-fat, low carbohydrate diet containing 65% fat, 15% carbohydrate, 20% protein (including 50 g fibre). Using the RMR collected in the initial visit (Visit 1), participants’ total daily estimated energy requirements will be calculated using RMR x an activity factor of 1.4 to give calories/day. The participants allocated to training will get an extra 100 kcal high-fat snack to consume on training days. During the days of diet control, participants will be instructed to abstain from alcohol. Participants who are habitual caffeine drinkers, will be instructed to consume caffeine as usual on all days. Meal times will be within +/- 30 min of 08:00 am, 13:00, and 19:30 to ensure the trial days are adequately matched. On the days of biopsies, dinner will be at 18:30. Participants will have a single 20 min face-to-face session with the dietitian at visit 1. Diet adherence will be assessed by a diet checklist, administrated by the dietitian. Exercise adherence will be assessed by exercise intensity, by the supervising exercise physiologist,