Inclusion Criteria:  Untrained participants will be defined as having a V̇O2peak of 30-45 ml.kg-1.min-1. Trained participants will be defined as having a V̇O2peak above 55 ml.kg-1.min-1 (females) and 60 ml.kg-1.min-1 (males). All participants will be between the ages of 18-40 years.  Exclusion Criteria:  Absolute contraindication to exercise testing or an orthopedic condition that may limit exercise testing as identified by standardized health screening tool (PAR-Q+). Pre-existing cardiac conditions (heart failure, congenital heart defect, valvular disease) that may limit exercise testing. A diagnosis of pulmonary hypertension. Current prescription drug use (excluding oral contraception for females). Pregnancy or lactation. Women of childbearing potential must be willing to use an acceptable method of contraception to avoid pregnancy throughout the study. Acceptable methods of contraception include tubal ligation, oral contraceptive, barrier methods (intra-uterine device, diaphragm, female condom, male condom). Abstinence is an acceptable form of contraception, only insofar as patients agree to use another acceptable method of birth control, preferably a barrier method, if they become sexually active. Postmenopausal female participants must be amenorrheic for ≥12 months.