abstract
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This thesis examined the effect of high-intensity "sprint" interval training (SIT) on aerobic-based exercise performance and metabolic adaptations in human skeletal muscle. It has long been recognized that several weeks of interval-based training increased skeletal muscle oxidative capacity; however, little was known regarding the minimum "dose" of SIT necessary to elicit this adaptive response or the time-course and magnitude of adaptation in other markers of skeletal muscle metabolic control. Our general hypothesis was that low-volume SIT would induce rapid improvements in a wide array of metabolic variables that were comparable to traditional high-volume endurance training (ET). Healthy young men and women were recruited to perform four to six 30- second "all out" Wingate Tests, three times per week with one to two days of recovery, for up to six weeks. The weekly dose of SIT corresponded to ~10 minutes of maximal cycling exercise (-225-300 kJ) over a total training time commitment of 60-90 minutes, including recovery. The SIT response was compared against control subjects who performed no training or an ET group who performed up to one hour per day of moderate-intensity cycling exercise, five days per week for six weeks (-2250 kJ per week). Our major findings were that one to two weeks of SIT increased performance during aerobic-based exercise (time-to-fatigue tests and time-trials of varying duration) and the maximal activity or total protein content of mitochondrial enzymes and transport proteins associated with carbohydrate metabolism (e.g., citrate synthase, cytochrome oxidase, glucose transporter 4). Six weeks of SIT or ET induced similar increases in markers of skeletal muscle carbohydrate (pyruvate dehydrogenase E1a protein content) and lipid oxidation (3-hydroxyacyl CoA dehydrogenase maximal activity) and peroxisome-proliferator-activated receptorgamma coactivator-1a protein content, and similar reductions in phosphocreatine and glycogen utilization during matched-work exercise. These data suggest that SIT is a time-efficient strategy to increase skeletal muscle oxidative capacity and to induce specific metabolic adaptations during exercise that are comparable to ET.