This thesis sought to advance our understanding of the physiological and health-related adaptations to low-volume interval training. Three separate studies were conducted in previously sedentary adults who trained three times per week. High-intensity interval training (HIIT) involved ten, 60-second cycling efforts at an intensity that elicited ~90% of maximal heart rate, interspersed with 60 seconds of recovery, whereas sprint interval training (SIT) involved three, 20-second ‘all-out’ cycling efforts interspersed with 2 minutes of recovery. Both protocols involved a brief warm-up and cool-down, resulting in 25- and 10-minute sessions for HIIT and SIT, respectively. Peak oxygen uptake (VO2peak), skeletal muscle mitochondrial content as reflected by the maximal activity and protein content of mitochondrial enzymes, and glycemic control based on oral glucose tolerance tests (OGTTs), intravenous glucose tolerance tests (IVGTTs) or continuous glucose monitoring (CGM), were determined before and after training. Study 1 found that 6 weeks of HIIT in the fed or fasted state increased VO2peak and mitochondrial content in women, but insulin sensitivity based on OGTTs was unchanged. Study 2 showed that 6 weeks of SIT increased VO2peak and mitochondrial content in men and women, whereas mean 24-hour glucose based on CGM was reduced in men only. Study 3 directly compared 12 weeks of SIT to traditional moderate-intensity continuous training (MICT) in men. The two protocols elicited similar improvements in VO2peak, mitochondrial content and insulin sensitivity based on IVGTTs, despite SIT involving a five-fold lower exercise volume and time commitment. This work advances our understanding of the potency of brief, intense exercise training to induce physiological remodeling and improve cardiometabolic health. It also highlights potential sex-specific adaptations to interval training that warrant clarification. Further investigation into the mechanisms of physiological remodeling to HIIT and SIT is needed, as are large-scale randomized clinical trials that compare these protocols to MICT. / Thesis / Doctor of Philosophy (PhD) / This thesis examined physiological and health-related adaptations to interval training, which involves brief bouts of intense exercise interspersed with recovery periods. One protocol involved alternating 60-second hard and easy cycling efforts for 20 minutes; the other involved three, 20-second ‘all-out’ sprints interspersed with 2 minutes of recovery. Both protocols improved indices of cardiometabolic health in previously inactive adults who trained three times per week for 6 weeks, even though the amount of exercise performed was lower than typically recommended in public health guidelines. When the latter protocol was directly compared against traditional endurance training, the improvement in cardiometabolic health after 12 weeks was the same, despite a five-fold difference in the total amount of exercise performed. Our findings highlight the effectiveness of short bursts of high-intensity exercise for improving health. These results may appeal to individuals who cite “lack of time” as a barrier to exercise.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/18080 |
| Date | 11 1900 |
| Creators | Gillen, Jenna |
| Contributors | Gibala, Martin, Kinesiology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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