Research Studies

1) 18-35 years old; men and women 2) Physical activity history: no regular physical activity (<20 minutes/day ? self report). Exercise will be proscribed for 3 days prior to study start. 3) Sleep/wake history: habitual sleep duration between 7-9.25h (determined by self-report during interview). a. During the screening process, subjects are asked questions about their present, past habitual sleep/wake schedule and nap times. Participants will be included if habitual sleep duration is > 7 and < 9.25h. We screen potential subjects who sleep < 7 or > 9.25h per night since there are significant medical and psychological disorders that are commonly associated with more extreme habitual sleep durations (e.g., depression, thyroid disease, sleep disorders, alcoholism). b. Subjects must be willing to maintain a 7 day consistent self-selected ~9h sleep schedule, which will be verified by wrist actigraphy, sleep logs, and either call-ins to a time stamped recorder or completing a secure, web-based survey program. 4) Altitude history: Potential subjects must have lived at Denver altitude or higher for at least 3 months to inpatient study to control for physiological adjustment to altitude (self-report by interview). 5) The subject must be able to read and understand the consent form and provide written informed consent, indicating the subject?s understanding of the purpose of the study and willingness to perform procedures described in the protocol. Our performance tests are in English and thus knowledge of English is a requirement.