Time and Nutrient-Dependent Effects of Aerobic Exercise on Metabolism in Adults (TANDEM Study)

Inclusion Criteria: * Age 18-40 years * Body Mass Index 18.5-\<40 kg/m2 * Recreationally active: defined as \>100 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 self-report of acute or chronic disease (cardiovascular disease (CVD), diabetes, pulmonary, gastrointestinal disorders, and orthopedic problems in particular). * No plans to relocate within the next 6 months. * No plans for extended travel (\>2 weeks) within the next 6 months. * Live or work within 30 minutes of the AHWC (exceptions may be made at the discretion of the Study PI on a case-by-case basis for highly motivated subjects). * 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 complete AM or PM exercise and complete 4 exercise sessions per week. * Ability to adhere to eating and exercise protocols (meal timing, exercising in fasted and fed states) * Willing and able to wear activity/sleep monitor for 7 consecutive days. * Willing not to enroll in any other formal weight loss or physical activity programs over the next 6 months. * For Females: * Not currently pregnant or lactating. * Not pregnant within the past 6 months. * Not planning to become pregnant in the next 6 months 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. * Hematocrit, white blood cell count or platelets significantly outside the normal reference range as measured on the screening visit. * 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). * Use of medications that would impact ability to achieve age-predicted maximum heart rate (e.g. beta blockers). * 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 exercise 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.