Title: “Limb and Inspiratory muscle metaboreflex activation in healthy males and females”
Supervisor: Dr. Bill Sheel
Committee members: Dr. Robert Boushel, Dr. Glen Foster
Abstract: Stimulation of type III and IV muscle afferents during exercise elicits a sympathetically-mediated increase in total peripheral resistance and blood pressure. This reflex response is termed the metaboreflex and is balanced by local metabolite-induced vasodilation to promote blood flow redistribution towards the exercising skeletal muscle. The metaboreflex has functional importance in maintaining blood pressure homeostasis, and in ensuring adequate skeletal muscle blood flow to match the increased energetic requirements of exercise. The metaboreflex is also present in the respiratory muscles, and results in the redistribution of blood flow to the respiratory muscles at the expense of the exercising limb muscles. This “competition” for blood flow between the respiratory and limb muscles likely has implications to the development of peripheral fatigue and exercise tolerance. Interestingly, the increase in blood pressure in response to both limb and inspiratory metaboreflex activation (LMA and IMA, respectively) is attenuated in females compared to males. This corresponds to the observed sex-based differences in peripheral muscle fatigue, with females generally being more resistant to fatigue. The basis of the sex-differences to LMA and IMA are not fully understood, but is suggested to result from the effect of ovarian hormones on blood pressure regulation. It is also unclear if the extent of the disparity in the pressor response between males and females is constant between muscle groups; specifically, if the sex-difference in the pressor response to LMA is of the same magnitude to that seen in response to IMA.
The purpose of this study is to compare the sex-based difference in the blood pressure response to LMA and IMA, at both absolute and relative workloads. This study will use forearm exercise and pressure-threshold loading to activate the limb and inspiratory metaboreflex, respectively. It is hypothesized that the increase in blood pressure during IMA will be equal to that which occurs during LMA, and that both responses will be attenuated in females. Findings from this study may provide insight to the mechanisms behind the sex-based differences in the development of peripheral fatigue and exercise tolerance.