Title: The effect of age and sex on the skeletal muscle metaboreflex
Supervisory Committee: Dr. William Sheel (Research Supervisor), Dr. Nisha Charkoudian, Dr. Glen Foster, Dr. Michael Koehle
University Examiners: Dr. Kristin Campbell, Dr. Jeffrey Richards
External Examiner: Dr. Ylva Hellsten
Chair: Dr. Maja Krzic
Abstract: The purpose of this thesis was to contribute to our understanding of the effects of ageing and sex on the skeletal muscle metaboreflex in the respiratory musculature (Chapter 2) as well as the limb during dynamic exercise (Chapters 3 and 4).
Methods: Chapter 2 investigates the effects of age and sex on the cardiovascular response to the intense inspiratory muscle work in young males and females relative to older males and females, post-menopause. Chapter 3 investigates the effect of sex on the cardiorespiratory response to the skeletal muscle metaboreflex evoked by dynamic exercise in young males and females. Chapter 4 investigates the effect of skeletal muscle mass on the cardiorespiratory response to the skeletal muscle metaboreflex evoked by intense, dynamic exercise in young males.
Conclusions: In Chapter 2 we found the blood pressure response to the respiratory muscle metaboreflex is augmented with healthy ageing. Additionally, the effect of sex observed in young females and males is absent in older adults when females are post-menopausal. In Chapter 3 we found that females continue to have an attenuated blood pressure response to the skeletal muscle metaboreflex in the context of whole-body, dynamic exercise; however, there is no effect of sex in the sympathetic activation of heart rate. The metaboreflex also has a greater influence on ventilatory control in males compared to females in dynamic exercise. Lastly, in Chapter 4 we found the mass of muscle stimulating the metaboreflex resulted in the dose-dependent arterial pressure and heart rate response following intense dynamic exercise. Additionally, we also found a ventilatory response to the metaboreflex can only be isolated with intense exercise and large muscle mass stimulus. Findings from this thesis suggest that circulating female sex hormones contribute to the attenuated arterial pressure response to the skeletal muscle metaboreflex when activated by the respiratory muscles and during dynamic exercise. Furthermore, the absolute mass activating the metaboreflex impacts the cardiorespiratory response to the metaboreflex even in the context of intense, dynamic exercise. Our findings point to age and sex differences in the control of blood flow during exercise.