Inclusion Criteria:  Being untrained based on a self-report of engaging in < 1 h of weekly moderate to vigorous physical activity based on the Canadian Society for Exercise Physiology Get Active Questionnaire. Having an estimated cardiorespiratory fitness in the lower 50% of adults in the specified age range based on the online fitness calculator available at: www.worldfitnesslevel.org. Females who are naturally cycling (i.e., not using any form of hormonal contraceptive) or are using a 2nd generation oral contraceptive.  Exclusion Criteria:  Experiencing a condition that might preclude safe participation in physical activity and exercise, as determined by answering "Yes" to any question on Page 1 of the Canadian Society for Exercise Physiology Get Active Questionnaire. Females with a positive pregnancy test.