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Abstract
Metabolic flexibility is the body’s ability to switch between fat and carbohydrates in response to exercise or eating. Historically this has been researched in response to meal challenges. However, exercise is an equally robust stressor on the body, which challenges underlying metabolic processes both at the muscular and whole body level. Exercise metabolism has been frequently assessed during steady state or ramped intensity exercise. High intensity interval exercise may, however, act as a test of exercise metabolic flexibility. Additionally, metabolism may be impacted by hormonal shifts, such as those seen in the menstrual cycle. The menstrual cycle can be separated in the low hormone follicular phase (days 1-14), and the high hormone luteal phases (days 16-28) separated by a ovulation, a one day estrogen surge (~day 15). These changes in hormones may impact exercise performance and how the body uses fats and carbohydrates. Estrogens positively influence metabolism in women by improving fat metabolism and performance in the first half of the menstrual cycle. However, these effects may be negatively impacted by high progesterone in the luteal phase or by hormonal oral contraceptive use. There also appears to be a need for additional research on sex differences in metabolism, as well as on the impact of hormonal contraceptives across on metabolic flexibility and its underlying mechanisms. The proposed project aims to draw connections between postprandial and exercise metabolism, and to investigate the impacts of sex and mitochondrial capacity on metabolic flexibility.