Paige A. Reinhard’s MSc Thesis Defence

Title: Exercise-Induced Diaphragm Fatigue With Superimposed Hypoxia

Thesis Supervisor: Dr. Bill Sheel
Committee Members: Dr. Michael Koehle, Dr. Jordan Guenette
Chair: Dr. Peter Crocker

Abstract: The mechanisms and sites that contribute to skeletal muscle fatigue vary depending on the specifications of the task, oxygen delivery, and fibre type composition. Due to anatomic and physiologic differences, men and women can have altered responses to a similar muscular fatiguing stimulus. The aerobic diaphragm muscle may exhibit neural protection under cases of potentially high fatigue, with a higher inhibition at the periphery. Hypoxia exacerbates key factors in diaphragm fatigue development, that may vary on the basis of sex. PURPOSE: The purpose of this thesis is to compare diaphragm fatigue between men and women under conditions of high-intensity exercise in normoxia and acute hypoxia. METHODS: 20 healthy participants (n=10 men) came into the lab on three occasions, the first day included pulmonary characterization and a maximal graded exercise test. The final two trial days randomize exercise in a normoxic or a hypoxic condition (FIO2 =0.21, 0.15, respectively). Cycling at ~85% VO2max till exhaustion, diaphragm force production was assessed via cervical magnetic stimulation pre- and post-exercise, and into recovery. RESULTS: There was no significant differences in the degree of diaphragm fatigue regardless of sex or FIO2. Time to failure in hypoxia was significantly shorter for both groups (men: p = 0.016, women: p < 0.05). A lowered FIO2 decreased up to 60-minutes into recovery for the female diaphragm more so than their male counterparts.  CONCLUSION: The authors conclude decreasing FIO2 during whole-body cycling exercise has little effect on the degree of diaphragm fatigue achieved. This result was found in both men and women. However, women had impaired recovery during hypoxia, whereas men have a similar recovery pattern in both conditions.