Inclusion Criteria:

• Age 18-55 years old.
• BMI 21.0 – 32.0 kg/m^2.

Exclusion Criteria:

• BMI > 32.0 kg/m^2.
• For the 20 participants who are involved in training - participation in structured exercise (>2 times per week for 30 minutes or longer).
• For the 10 participants in the aerobic arm - do not participate in structured exercise > 5 times per week.
• For all participants - cardiovascular, metabolic (type 2 diabetes, fasting plasma glucose at or above 110 mg/dL and untreated hypo- or hyperthyroidism) or renal disease, orthopedic problems that would keep them from being able to perform leg extensions; medications that are known to have an impact on mitochondrial function: 
  • Corticosteroids, opiates, benzodiazepines, tricyclic antidepressants, beta blockers, sulfonylureas, insulin, anticoagulants, barbiturates, insulin sensitizers, fibrates (PPAR gamma agonist), smoking, pregnancy. 
  •