Effects of exercise mode on human skeletal muscle and circulating biological networks

The effects of a single bout of high intensity interval training (HIIT) versus a single bout of work-matched continuous endurance exercise on skeletal muscle and circulating biological networks will be investigated in healthy young males. Overview of design: Ten healthy sedentary males aged between 18 – 30 years old with a body mass index (BMI) of 18.5 – 24.9 kg/m2 will be recruited to participate in a randomised cross-over study. All participants will complete the HIIT (vigorous intensity; Borg RPE scale 15-16; 5 x 1 minute of cycling at 85% of maximal Watts [Wmax] with 1 minute break in between each interval) and endurance exercise (moderate to vigorous intensity; Borg RPE scale 13-14; 10 minutes of continuous cycling at 50-55% Wmax) protocols in random order on two separate occasions with a minimum 10-day washout between trial days. Baseline testing (body composition data, resting metabolic rate and aerobic capacity) and exercise protocol familiarisation will precede the first trial day. Aerobic capacity, familiarisation and exercise testing sessions will all be conducted one-on-one with a trained exercise scientist, who will also monitor session attendance and adherence to exercise protocols. Rating of perceived exhaustion (RPE) and heart rate will be monitored during aerobic capacity, familiarisation and exercise testing sessions. Trial days will involve skeletal muscle biopsy and blood sampling before, during, immediately following, 1 hour post and 3 hour post exercise. Procedures: Baseline testing and trial days will take place at the Exercise Science laboratory within the Daniel Mannix Building at Australian Catholic University, Melbourne. Participants will attend the laboratory for 5 visits outlined below. Visits 1-3 will occur over a total period of 1-2 weeks. Following these visits, a minimum of 10 days will separate the two trial days (Visits 4 and 5). Visit 1: Participant meets with researchers to have the study procedures explained prior to obtaining written consent. Additional paperwork including exercise and muscle biopsy screening tools are completed. Visit 2: Baseline measurements visit: Resting metabolic rate (RMR), Dual-Energy X-Ray Absorptiometry (DXA) and maximal effort cycling (VO2peak) test. Visit 3: Exercise familiarisation and collection of standardised meal to consume prior to each trial day. During this exercise familiarisation visit, the participant will complete both exercise protocols with each exercise protocol lasting a total of 8-12 minutes (approximately 30 minutes total including warm up and warm down). The two exercise protocols will be separated by a rest period of 15-30 minutes. Visit 4: Trial day 1: Participants will attend the lab in the morning following consumption of a provided standardised meal the night prior to the trial day and following an overnight fast. A cannula will be inserted and the first muscle biopsy will be obtained. Participants will complete the first randomly assigned exercise protocol (8-12 minutes; approximately 30 minutes total including warm up and warm down), including muscle biopsy and blood sampling. Visit 5: Trial day 2: Participants will attend the lab in the morning following consumption of a provided standardised meal the night prior to the trial day and following an overnight fast. A cannula will be inserted and the first muscle biopsy will be obtained. Participants will complete the second randomly assigned exercise protocol (8-12 minutes; approximately 30 minutes total including warm up and warm down), including muscle biopsy and blood sampling. Description of study procedures: Resting Metabolic Rate test: Participants will lie down in a quiet, dim-lit room for 25 minutes 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. This test requires the participant to be fasted with no food, fluid or exercise/activity prior to the test. Body composition assessment: Participants will undergo a whole body DXA scan. Participants will lay supine on the scanning bed for the duration of the 7-15 minute scan (depending on scanning mode; thick or standard; according to weight 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 the machine and scans to be used in this study by a Medical Physicist. This test requires the participant to 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 needed), and all jewelry must be removed. All measures will be obtained 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. Aerobic capacity [VO2 peak] test: Aerobic capacity will be assessed by measuring the maximum volume of oxygen (VO2) participants can breathe in and transport to the working muscles while exercising at maximal intensity. After a light 10-minute warm-up on a cycling ergometer (exercise bike), participants will pedal at a fixed intensity (watts) that will increase every 1-2.5 minutes until volitional fatigue. During this test participants will wear a mouthpiece and headpiece that is connected to a tube for the collection of expired air. Following the warm-up, the test will last for 10-15 minutes where the last few minutes should be perceived as exhaustive. A warm-down will be completed after the test finishes. The aerobic capacity test is a vigorous intensity exercise protocol with intensity assessed by RPE, heart rate and oxygen uptake. The total duration of the aerobic capacity test including the warm up, testing and warm down will be approximately 30 minutes. Muscle biopsy sampling: All muscle biopsy sampling is conducted by an experienced sports medicine physician. In preparation for a biopsy, a small amount of local anesthetic is injected under the skin, which may result in a mild burning sensation while the fluid is injected. A small, 4-5 mm incision is then made into the skin to create an opening for the biopsy needle. There is often a small amount of bleeding from the incision; however, this bleeding is generally minimal. The biopsy needle is then inserted through the incision site. A small amount of muscle (100-200 mg) is collected and frozen immediately in liquid nitrogen. After each biopsy, the incision will be closed with sterile tape and wrapped with a bandage. Across the 2 trials, a total of 10 muscle biopsy samples will be taken (5 per trial day). Blood sampling: An in-dwelling venous cannula will be inserted by the doctor performing the muscle biopsies to collect a total of 10 blood samples (12 mL each) equating to a total volume of 120 mL across the entire study period.