Effects of high intensity interval training in hypoxia on insulin sensitivity in overweight and sedentary individual

Potential participants will be initially screened by the primary investigator. Participants who meet the eligibility criteria will then be invited to the Exercise Physiology Lab at Murdoch University. Written informed consent will be obtained from all participants prior to participation. Baseline assessments including anthropometric measurements, physiological parameters, and metabolic status will be undertaken before the start of the exercise training program. This study will adopt a 10-week Randomised Controlled Trial design; participants will be allocated to a 10-week training program that will either be performed in normal ambient conditions (normoxia) or in low oxygen conditions (i.e., hypoxia). Procedure: All participants will be required to complete a 10-week training program. Specifically, participants will complete three supervised exercise training session per week, at the Strength and Conditioning Laboratory in Murdoch University. Each training session will consist of both an aerobic and resistant exercise component, with an approximate session duration of 60-75 min. All participants will undergo a standardised training for the first 2 weeks. After the 2 weeks of standardised training, participants will be allocated to either a group that performs the aerobic exercise in hypoxia or the group that performs the aerobic session in normoxia. The resistance exercise will always be conducted in normal ambient conditions. All training sessions will be supervised by an exercise physiologist. Exercise adherence will be assessed for all participants in the research by the exercise physiologist conducting the training sessions. The total number of sessions completed, as well as workload (during the interval training) and the number of repetitions and weight lifted (during the resistance training), will be recorded to determine adherence to the program. Standardized training (First 2 weeks) During each session, participants will first perform 20 min of high intensity interval cycling which will consist of four, 1-min cycling bouts interspersed with 4 min of recovery. Specifically, participants will perform the work and recovery bouts at a perceptually regulated intensity corresponding to a RPE of 16 (between 'hard' and 'very hard'; 6-20 Borg scale) and 10 ('very light' and 'fairly light'), respectively. Following 10 min of rest, participants will then perform four different resistance exercise involving the major muscle groups (i.e., leg press, bench press, lateral pulldown and overhead press). The weights will be individually adjusted to ensure that participants achieve 12-15 repetitions for each set. All participants will perform 3 sets of each resistance exercise, with 60 s of rest between sets. Hypoxia screening (Prior to hypoxia training) Upon completion of the 2-week standardized training, participants will then be randomly allocated into either the exercise with hypoxia (Ex+H) or exercise without hypoxia (Ex) group for the final 8 weeks. Prior to the hypoxia training, all participants (allocated to hypoxia training group) will be required to undergo a hypoxia screening test. Participants will be fitted with a facemask connected via corrugated plastic tubing to a portable hypoxic generator under passive resting conditions. Participants will first be exposed to a hypoxic dose of FiO2 ~0.18 (equivalent to ~1200m) for 5 min. The facemask will then be removed, so that participants will breathe normal air (i.e. FiO2 0.21). An identical procedure will be performed for a hypoxic dose of FiO2~0.16 and FiO2~014. Arterial oxygen saturation (SpO2) will be measured continuously (1Hz) via a pulse oximeter. It is expected that rapid re-oxygenation will occur immediately upon removal of the facemask i.e., within seconds, with recovery to baseline SpO2 (of 98-100%) within a minute. Hypoxia training (Final 8 weeks) The targeted FiO2 for the hypoxia training is 0.14 (i.e., ~3000m). However, to ensure that participants are accustomed to hypoxia, the FiO2 will be set at 0.18 during the first training session (in week 2) and gradually decreased to 0.14 by the end of week 4. Participants will only perform the interval training in hypoxia (i.e., four, 1-min cycling bouts interspersed with 4 min of recovery); Hypoxic exposure will be implemented throughout the entire high intensity interval exercise. All hypoxia training sessions will be conducted in an environmental chamber. All resistance training will be performed in normal ambient conditions. For the final 4 weeks (week 7 to 10), participants will perform the same high intensity interval exercise with the exception that the total duration will be increased to 30 min (i.e., total of 6, 1-min cycling bouts, interspersed with 4 min of recovery). The specificities of the resistance training will remain the same (as the first 2 weeks) during this 8 weeks of training, with the exception that the intensity will be progressively increased. Specifically, weights will be gradually increased to ensure that individuals achieve 12-15 repetitions (per set) during week 1-4 and 8-12 repetitions during week 5-10. The training session from week 1 to 6 will take approximately 60 min (per session) whilst the final 4 weeks will take approximately 75 min. Following the completion of the training program (i.e., week 10), participants will complete their post-intervention assessments, which will be identical with the baseline measurements, at least 24 h but not more than 96 h after the last training session.