ImpaCt Of Shiftwork on METabolic Flexibility and Skeletal Muscle Clocks

Inclusion Criteria: * Age 21-45 yrs * Employed as a healthcare worker in either dayshift (N=15) or nightshift work (N=30). * Nightshift is defined as 12 months of consecutive nightshift work, who had 10 or more nightshifts per month (6 h between 10 PM and 8 AM, with no shift duration \> 12 h). * Dayshift is defined as 12 months of consecutive dayshift work, who had 10 or more dayshifts per month (6h between 8 AM and 10 PM, with no shift duration \> 12 h). * Weight Stable (+/- 3 kg over past 6 months) * BMI between 18.5-29.9 kg/m2 * Understands the procedures and agrees to participate by giving written informed consent * Willing and able to comply with scheduled visits, laboratory tests, and other study procedures including * Only low to moderate caffeine users (\<500 mg/day, or up to approximately 5 cups \[1 cup=8 ounces\] of coffee/day. Exclusion criteria: * Acute or chronic medical conditions or medication that would contraindicate participation in the research testing or could potentially affect metabolic function including, but not limited to: * History or presence of cardiovascular disease (unstable angina, myocardial infarction or coronary revascularization within 6 months, presence of cardiac pacemaker, implanted cardiac defibrillator) * Type 1 or Type 2 diabetes mellitus * Obesity (BMI ≥ 30 kg/m2) * Bleeding and clotting disorders * Uncontrolled hypertension (BP \>160 mmHg systolic or \>100 mmHg diastolic) * Acute or chronic infections (such as TB, HIV, or Hepatiti…