Inclusion Criteria:  Between the ages of 18-50 years No medical history of cardiovascular, respiratory, nervous system, or metabolic disease. Women must be pre-menopausal.  Exclusion Criteria:  Participants with any known cardiovascular, respiratory, nervous system, or metabolic disease. Having travelled above 2,000m within 1 month of testing at low and high altitude. Women who are pregnant, confirmed by a pregnancy test. Women who are post-menopausal. Participants that are classified as obese (body mass index > 30 kg/m2). Participants who are current daily smokers. Participants that are currently taking monoamine (MAO) inhibitors, or tricyclic antidepressants.