Browsing by Author "Inglis, Erin Calaine"

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    Characterizing the effect of precise exercise intensity prescription on physiological adaptations to endurance training - an intensity domain-specific approach
    (2023-06) Inglis, Erin Calaine; Murias, Juan M; Reimer De Bruyn, Raylene A; Keir, Daniel A; Aboodarda, Saied Jalal; Boone, Jan; Townsend, Nathan E
    Exercise intensity determines the magnitude of the metabolic disturbance which is directly related to the upregulation of signalling pathways responsible for the adaptative responses to exercise training. The exercise intensity domain schema describes four distinct domains (i.e., moderate-, heavy-, severe- and extreme-intensity) each characterized by distinct metabolic responses. These domains are separated by exercise thresholds – of which the position varies widely between individuals. The most commonly used endurance exercise intensity prescription approach utilizes a percentage of maximal values (i.e., maximal oxygen uptake (V̇O2max) or maximal heart rate (HRmax)) to assign intensity. However, a major limitation to this approach is that it ignores the existence of individual exercise thresholds and the exercise intensity domains they create. This is problematic as research has shown that a given percentage of maximal values does not ensure a homogenous metabolic disturbance across individuals which complicates the interpretation of previous research studies that utilized this approach. Therefore, the true contribution of exercise intensity in modulating changes in response to endurance exercise training is unknown. The aim of this thesis was to apply a domain-based approach that precisely accounts for the metabolic disturbance of the intervention, to allow for the determination of the true effect of intensity on V̇O2max, submaximal thresholds, oxygen uptake (V̇O2) kinetics, and central and peripheral adaptations. The main findings were that i) changes in V̇O2max were intensity-domain dependent such that, with the exception of sprint interval training (SIT), greater magnitudes of change were found with progressively greater intensities with severe-intensity exercise (i.e., high-intensity interval training) producing the greatest magnitude of change, ii) this intensity-domain dependency was less pronounced when evaluating changes in the estimated lactate threshold and the maximal metabolic steady state and did not apply to the extreme-intensity domain (i.e. was not evident with SIT), iii) greater intensities of exercise resulted in central adaptations (i.e., maximal cardiac output and maximal stroke volume), with evidence for some peripheral adaptations to be present as well, iv) when compared to control, there was an equal speeding of V̇O2 kinetics across intervention with no significant correlations between changes in the speed of V̇O2 kinetics and performance variables.
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    Does the plateau in the NIRS-derived [HHb] signal in the vastus lateralis represent the upper limit in O2 extraction during ramp incremental cycling?
    (2018-09-10) Inglis, Erin Calaine; Murias, Juan M.; Millet, Guillaume Y.; Passfield, Louis
    Oxygen (O2) extraction and O2 delivery represent the two critical components for muscle metabolism and have been extensively studied. The near-infrared spectroscopy (NIRS) derived O2 extraction signal ([HHb]) has been widely used for characterizing the peripheral response to exercise. Research examining this signal in response to ramp-incremental cycling has identified a linear increase followed by a plateau ([HHb]PLATEAU) prior to the achievement of maximal oxygen uptake (V̇O2max). Despite the common occurrence of this plateau, beyond speculation no research has been conducted to examine the underlying mechanisms causing the plateau in this signal. The studies in this thesis contribute to the understanding of the mechanisms that mediate the [HHb]PLATEAU by examining the maximal achievable level of O2 extraction at the end of a ramp-incremental test in different populations. In this two-part study 26 subjects were tested and divided into groups based on sex and training status. The results from the first part of this study demonstrated the existence of a reserve in O2 extraction and suggest that the [HHb]PLATEAU does not represent the upper limit of extraction in the vastus lateralis muscle. Additionally, the second part of this study revealed that sex and training status do not influence the amplitude of the reserve.