Skeletal Response to Simulated Night Shift

Inclusion Criteria * Healthy, nonpregnant adults 20-40 years old who habitually sleep 7-9 hours during the biological night o Women must be premenopausal, on continuous combination oral contraception and not breastfeeding. * Willing and able to complete a sleep diary, wear a wrist actigraphy monitor and complete a 3-6 week research study including two 4-night inpatient stays. * Fully vaccinated against SARS-CoV-2, and willing to produce a negative COVID test result before their first inpatient stay. Exclusion Criteria * Regularly go to sleep after midnight. * Night shift work within 1 year prior to study. * Travel \> 1 time zone within 4 weeks prior to the study or need to travel \>1 time zone during study. * Physical activity level/regimen incompatible with inpatient CTRC stay. * Current smokers (or within the previous year of study) * Positive drug test at screening or inpatient admission * BMI \> 30 kg/m2 * Individuals who are concurrently participating in another research protocol that would influence their safe participation in this study. For example, participants involved in a study that requires blood draws or ingestion of experimental medication as this would increase the risk of participation in our study and/or compromise study results. * Any clinically significant unstable medical or surgical condition within the last year (treated or untreated), including history of a clinically significant abnormality of the neurological system (including cognitive disorde…