This is a longitudinal study supported by Pfizer and is a collaboration between DMPI (Duke Molecular Physiology Institute) and DIAL (Duke Image Acquisition Laboratory) to measure the effects of acute exercise on carnitine and acylcarnitine levels in the muscle and on insulin sensitivity in the plasma. This pilot study seeks to explain why moderate intensity exercise provides more improvements in glucose control for pre-diabetic patients than vigorous intensity. The investigators hypothesize that moderate intensity exercise might be beneficial for elderly individuals who are overweight or obese, specifically by: 1. Reducing damaging excess protein acetylation (measured in muscle biopsy), 2. Improving the acylcarnitine/carnitine ratio (measured by MRS), 3. Improving overall mitochondrial function as reflected in reduced phosphocreatine recovery time (measured by MRS) and 4. Increasing insulin sensitivity as measured by a 4-hour oral glucose tolerance test. Investigators intend to use the results of this study to show feasibility in measuring mitochondrial function at Duke for a larger federal grant submission. Investigators hypothesize that carnitine insufficiency might contribute to mitochondrial dysfunction and obesity-related impairments in glucose tolerance and insulin action.

Inclusion Criteria:

• Age: 60-80 years
• Moderately Overweight: BMI - 25.0 - 35.4
• Sedentary - exercise ≤ 1 day/week
• Fasting plasma glucose: > 100 - < 126 mg/dL
• Readings from two separate days

Exclusion Criteria:

• Orthopedic limitations, musculoskeletal disease and/or injury

• Allergic to xylocaine

• Inability to give blood continuously through an intravenous catheter

• Have a confounding medical condition that is progressive and unstable such as HIV, Hepatitis C, active cancer, and/or taking medications for those conditions that are likely to confound the assessment of pre-diabetes

• Prior surgical operation within the past 6 months

• Prior injury to the eye involving metallic objects or fragments

• Prior injury involving a metallic object or foreign body (eg. BB, bullet, shrapnel, etc.)

• Tattoos from the waist down to the feet

• Any of the following implants or devices

  • Aneurysm clip
  • Cardiac pacemaker
  • Implanted cardioverter defibrillator (ICD)
  • Electronic implant or device
  • Magnetically activated implant or device
  • Neurostimulation system
  • Spinal cord stimulator
  • Internal electrodes or wires
  • Bone growth/bone fusion stimulator
  • Cochlear, otologic or other ear implant
  • Insulin or other infusion pump
  • Implanted drug infusion device
  • Eye implants
  • Vascular access port and/or catheter
  • Wire mesh implant or stent
  • Other implant

• Claustrophobia

• Prior knee replacement surgery

• Pregnant or intending to become pregnant during the study