Sex Differences in Cold-Induced Changes in Maximal Fat Oxidation

Inclusion Criteria: * Age 18-40 years (inclusive) * Weight stable (no change in body mass greater than 5 lbs. within the previous 6 months. * Willing to abstain from caffeine and alcohol for 24-hours prior to two different study visits * Competency in English as informally assessed by comprehension of the Informed Consent. This study involves maximal exercise testing; for safety reasons, the ability for clear and rapid communication will be necessary between the research participants and the investigators. * Regular exercise (i.e., at least 150 minutes of moderate-vigorous exercise per week) Exclusion Criteria: * Use of hormonal contraceptives * History of autonomic, cardio-pulmonary, and/or metabolic disease (including heart failure, hypertension, arrhythmia, vascular disease, and/or diabetes) * Pregnancy or breast feeding * Habitual use of tobacco/nicotine products or recreational drugs (2 or more uses within the previous month)