Examining Sex Differences in Substrate Utilization During Threshold-Based Exercise Prescription

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Pacitti, Lauren J.
Exercise prescription , Metabolic stress , Lactate Threshold , Critical Power
The traditional “relative percent method” (TRAD) of prescribing exercise (e.g. % of maximal oxygen uptake [%VO2max]) elicits sex specific amounts of metabolic stress and ratios of carbohydrate to fat oxidation that result in a lower steady-state respiratory exchange ratio (RER) in females. Differences in exercise response may be explained by differences in metabolic stress and muscle oxygenation linked to sex-based differences in lactate threshold (LT) and critical power (CP). Thus, the purpose of this thesis was to examine the effect of threshold-based exercise prescribed (THR) using LT and CP to determine whether using THR – specifically, an intensity anchored halfway between LT and CP (Δ50) - eliminates differences in substrate utilization, metabolic stress and muscle oxygenation between sexes. 13 females and 13 males completed preliminary LT and CP testing. Continuous cycling was performed twice at Δ50 for 45 minutes whilst recording RER, blood lactate (BL), heart rate, rate of perceived exertion (RPE) and tissue oxygenation. No difference in RER, BL or RPE between sexes was observed. Significant effects of sex and interaction (time x sex) (p<0.05) were observed in (oxygenated hemoglobin) O2Hb during Δ50. Our results suggest sex differences in tissue oxygenation but not RER are present during THR. The potential for THR in future training studies merits investigation.
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