MacInnis, MartinTripp, Thomas2025-01-172025-01-172025-01-10Tripp, T. (2025). Acute and chronic physiological responses to endurance exercise of varying durations: neuromuscular, hematological, and integrative outcomes (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.https://hdl.handle.net/1880/120430The integrative action of several physiological systems supports increased skeletal muscle energy demand during exercise. Physiological systems structurally and functionally adapt when exercise stresses are regularly imposed during a period of training. These adaptations, in turn, reduce the homeostatic stress for a given exercise bout. In particular, the impacts of exercise duration and exercise frequency on acute and chronic exercise responses are poorly understood. During prolonged exercise, physiological systems are activated to support muscle contraction, but metabolite accumulation and substrate depletion inevitably occur. During a training program, the balance between the number of times an exercise stress is experienced and the amount of stress per instance implicates exercise frequency along with duration as factors influencing physiological adaptations. This dissertation sought to address gaps in our understanding of the acute responses to differing exercise durations, and to compare chronic training adaptations when total exercise volume is the same. Study 1(Chapter III) showed that near-infrared spectroscopy measures of muscle oxidative capacity are sensitive to contraction intensity, necessitating intensity controls when the technique is used in future studies. Study 2 (Chapter IV) characterized neuromuscular fatigue kinetics during high-intensity interval training and showed that the largest deficits occur early during exercise, implying that additional exercise stress diminished during later bouts. Study 3 (Chapter V) investigated erythropoietic signalling when exercise duration is doubled. I found that increases in erythropoietin mass were not different after both exercise durations, despite hypervolemia only occurring after longer exercise. Study 4 (Chapter VI) aimed to probe whether the acute differences I found between exercise durations impacted training adaptations. This study showed that both long, low-frequency (a Weekend Warrior pattern) and shorter, high-frequency training similarly improved maximal oxygen uptake, hemoglobin mass, muscle oxidative capacity, and exercise capacity. The findings of this dissertation suggest that for some exercise responses, duration does not substantially augment the magnitude of acute stress/signalling events; however, when comparing different frequencies of exposure to that exercise stress, training adaptations were not different. Future studies should address how this acute stress/signal-to-chronic adaptation discrepancy occurs in the context of exercise duration and training frequency.enUniversity of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.High-intensity interval trainingHemoglobinSkeletal muscle oxidative capacityNeuromuscular fatigueOxygen uptakeExercise performancePhysiologydoctoral thesis