This study plans to learn more about whether exercise can help protect the body from health problems that happen when a person's sleep and daily schedule are out of sync with their natural body clock (circadian rhythm).

This study plans to learn more about whether exercise can help protect the body from health problems that happen when a person's sleep and daily schedule are out of sync with their natural body clock (circadian rhythm). Specifically, this study will help us understand whether exercise can help protect the body from health problems that happen when a person's sleep and daily schedule, due to night shift work, are out of sync with their natural body clock.

Inclusion Criteria:

• Age 18-40 years
• Body Mass Index 18.5-<40kg/m^2
• Physically inactive: defined as <150 minutes per week of voluntary exercise at moderate intensity or greater and <60 min per day of total habitual physical activity (i.e., work related, transportation related) at moderate intensity or greater, over the past 3 months.
• No plans to relocate within the next 6 months.
• No plans for extended travel (>2 weeks) within the next 3 months.
• Capable and willing to give informed consent, understand exclusion criteria, and adhere to study conditions.
• Have a primary care physician (or are willing to establish care with a primary care physician prior to study enrollment) to address medical issues which may arise during screening or study procedures.
• No contraindications to exercise or limitations on ability to be physically active.
• Ability to adhere to sleeping, eating, and exercise protocol
• Willing and able to wear activity/sleep monitor for 7 consecutive days.
• For Females:
• Not currently pregnant or lactating.
• Not pregnant within the past 6 months.
• Not planning to become pregnant in the next 6 months
• Regularly timed menstrual cycles to facilitate measurement of EE in the early follicular phase.

Exclusion Criteria:

• Diastolic blood pressure >100 mmHG, systolic blood pressure >160 mmHG, or resting heart rate >100 bpm as measured in duplicate on the screening visit after 5 minutes of rest in a seated position.
• Diabetes (fasting glucose >/=126 mg/dL or Hemoglobin A1C >/=6.5%) as measured during the screening visit.
• Undiagnosed hypo- or hyper-thyroidism (TSH outside of the normal range as measured during the screening visit) or history of uncontrolled thyroid disorder. History of thyroid disease or current thyroid disease treated with a stable medication regimen for at least 6 months is acceptable.
• Triglycerides >400 mg/dL as measured on the screening visit.
• LDL cholesterol >200 mg/dL as measured on the screening visit.
• Abnormal resting electrocardiogram (ECG) as measured on the screening visit: serious arrhythmias, including multifocal PVC's, frequent PVC's (defined as 10 or more per min), ventricular tachycardia (defined as runs of 3 or more successive PVC's), or sustained atrial tachyarrhythmia; 2nd or 3rd degree A-V block, QTc interval > 480 msec or other significant conduction defects.
• Presence or history of any metabolic or chronic health problems which would affect appetite, food intake, energy metabolism, or ability to participate in exercise: CVD, peripheral vascular disease, cerebrovascular disease, significant cardiac arrhythmias or cardiac valve disease, diabetes, uncontrolled hyper- or hypothyroidism, uncontrolled hypertension, cancer (within the last 5 years, except skin cancer or other cancers considered cured with excellent prognosis), HIV infection, significant renal, musculoskeletal, neurologic, hematologic, or psychiatric disease.
• Significant gastrointestinal disorders including: chronic malabsorptive conditions, peptic ulcer disease, Crohn's disease, Ulcerative Colitis, chronic diarrhea, or active gallbladder disease.
• Significant pulmonary disorders including: chronic obstructive pulmonary disease (COPD), interstitial lung disease, cystic fibrosis, or uncontrolled asthma.
• Symptoms suggestive of CVD: chest pain, shortness of breath at rest or with mild exertion, syncope.
• Regular use of prescription or over-the-counter medications known to significantly impact appetite, weight, or energy metabolism (e.g., appetite suppressants, lithium, stimulants, anti-psychotics, tricyclic antidepressants).
• Regular use of systemic steroids (other than Oral Contraceptive Pills).
• Regular use of obesity pharmacotherapeutic agents within the last 6 months.
• Current alcohol or substance abuse.
• Nicotine use (past 6 months).
• Current severe depression or history of severe depression within the previous year, based on DSM-IV-TR criteria for Major Depressive Episode. Score > 16 on the Center for Epidemiologic Studies Depression Scale (CES-D) will require further assessment by the Study MD to determine if it is appropriate for the subject to participate
• History of other significant psychiatric illness (e.g., psychosis, schizophrenia, mania, bipolar disorder) which in the opinion of the Study MD would interfere with ability to adhere to the study conditions.
• Weight loss >5% in past 3 months.
• Currently participating in or planning to participate in any formal weight loss or physical activity programs or clinical trials.
• Primary sleep disorders including but not limited to insomnia, obstructive sleep apnea, periodic limb movements in sleep, restless leg syndrome.
• Night-time shiftwork, rotating work, or other circadian disruptions and disorders (e.g., diagnosed delayed sleep-wake phase disorder).
• Self-reported long (>9.25h) or short sleep (<7h) that would make adhering the exercise conditions difficult.
• Regular use of prescription or over-the-counter medications known to affect sleep (e.g., benzodiazepines, doxepin, zolpidem, trazodone, diphenhydramine HCl, etc.).
• Regular use of melatonin (>/=2 days per week).
• High consumption of caffeine (>500 mg/d) or unwilling to abstain from caffeine consumption during run-in and in-patient protocol.
• Planned travel >1 time zone away 4 weeks prior to study start or at any time during study protocol.