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)