Inclusion Criteria:  Between the ages of 18-35. Currently meeting the American College of Sports Medicine's recommended guidelines of activity (at least 90 min/week of moderate and/or vigorous physical activity). Willing to participate for 4 days (2 visits) and refrain from exercise outside of the lab for 4 days (1 day before and the day of two visits).  Exclusion Criteria:  Any known history of cardiac, pulmonary, or metabolic disease (e.g. cardiovascular disease, asthma, diabetes). A current musculoskeletal injury, mental illness (e.g., depression, anxiety, or stress disorders), or sleep disorder.