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Bruce, Christina Dominique

University of British Columbia

When the availability of oxygen within the atmosphere is reduced (i.e., hypoxic hypoxia) there are numerous adaptations that take place over time within the human neuromuscular system. However, less is known about intrinsic muscle contractile properties under hypoxic conditions when studied in vivo, and whether or not hypoxia influences these properties following varying lengths of time at high altitude (HA). Using non-volitional (i.e., electrically-evoked) contractions, it has been established in male participants that the intrinsic neuromuscular fatigability is exacerbated with acute hypoxia and recovers following acclimatization to HA; however, it is currently unknown how acute and prolonged exposures to hypoxia influence intrinsic neuromuscular fatigability of females. Therefore, the studies within this dissertation have utilized external electrical stimulation of the human neuromuscular system to determine if muscle contractility and fatigability change with acute and prolonged exposures to hypoxia. When simulating HA at sea level, a two-hour exposure to hypoxia led to increased contractile speeds and a rightward shift to the torque-frequency relationship of the dorsiflexors. Post-activation potentiation of the quadriceps muscle was not affected by simulated hypoxia at sea level, or after sojourning to HA (3800 m) for 1-2 and 11-13 days. However, potentiation of the maximal compound muscle action potential increased with altitude for males following 11-13 days at 3800 m and remained unchanged in females. For male participants, quadriceps fatigability was exacerbated by 1-2 days at altitude and did not recover following acclimatization of 11-13 days. In contrast, fatigability was unaffected by HA for females. These findings contribute to our collective understanding of how the neuromuscular system acclimatizes to hypoxia, and highlight the need for more research regarding female physiology at HA.

Text

2024-08-22

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/89008

Kinesiology

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/