Thesis Defence: Investigating the Sex-Based Differences in the Locomotor Muscle Metaboreflex Activation at High Altitude
July 24 at 9:00 am - 1:00 pm
Katherine M. Taylor, supervised by Dr. Glen Foster, will defend their thesis titled “Investigating the Sex-Based Differences in the Locomotor Muscle Metaboreflex Activation at High Altitude” in partial fulfillment of the requirements for the degree of Master of Science in Health and Exercise Sciences.
An abstract for Katherine M. Taylor’s thesis is included below.
Defences are open to all members of the campus community as well as the general public. Registration is not required for in-person defences.
Abstract
The locomotor muscle metaboreflex (LMM) is essential in the exercise-mediated cardiovascular response, coordinating blood flow distribution to support skeletal muscle’s metabolic demands. At low altitudes (LA: < 1,500 m), LMM sensitivity is reduced in females, and whether sex-based differences in the LMM persist at high altitudes (HA: > 2,500 m) is unknown. Utilizing the effects of post-exercise circulatory occlusion (PECO), via lower-limb cuff inflation to 220 mmHg, allows for continued stimulation of the LMM while isolating it from concurrent reflexes (i.e., central command, arterial baroreflex), thereby trapping exercise-produced metabolites within the skeletal muscle. We hypothesized that the cardiorespiratory responses to PECO would be attenuated in females compared to males during sub-maximal cycling exercise, at both LA (1,045m; Calgary, Canada) and HA (3,500m; La Paz, Bolivia). Twenty healthy participants (age = 31 ± 7 years), females: n = 10, completed a 2-day protocol that was repeated at LA and HA. First, a maximal cardiopulmonary exercise test to determine participants’ gas exchange threshold (GET) for use in sub-maximal testing. Twenty-four to forty-eight hours later, participants sub-maximally cycled at the workrate corresponding to GET, followed by a round each of control or PECO, in randomized order. The changes in minute ventilation (∆V̇E), heart rate (∆HR), and mean arterial pressure (∆MAP) served as indicators of LMM sensitivity. Maximal exercise tests were repeated on days 1-3 of acclimatization to 3,500 m, sub-maximal tests were repeated on days 6-10. During occlusion, the absolute difference between control and PECO for ∆V̇E was not different from females to males (4 [6, 15] l/min; P=0.308) and no different at HA (1 [-6, 8] l/min; P=0.698). ∆HR was not different in females compared to males (2 [-9, 14] beats/min: P=0.624), nor HA compared to LA (5 [-4, 14] beats/min; P=0.145). ∆MAP was not different between sexes (3 [-4, 10] mmHg; P=0.249), or altitudes (3 [-3, 8] mmHg; P=0.192). Our results demonstrate there was no difference between sexes in LMM sensitivity at LA or HA. Suggesting that LMM sensitivity at HA may depend on other sex-based cardiopulmonary factors (e.g., cyclic ovarian hormones) or central command.
