This is a small pilot aerobic training trial designed to examine differences between normal-high and low vitamin D levels and 7-days of aerobic training on local VO2 measured by non-invasive Hybrid Diffuse Optical Spectroscopy.

Inclusion Criteria:

• 65-75 years of age

Exclusion Criteria:

• Currently have or have a history of cardiovascular or pulmonary disease that would preclude the involvement in the performance of exercise.
• Uncontrolled diabetes or hypertension.
• History of neurological conditions related to spinal derangement, disk disease, peripheral neuropathies, tremor and rigidity
• History of leg/hip trauma, inflammation, infection rhabdomyolysis, or leg surgery in the past 3 months
• Have a diagnosis of osteoporosis (as determined by DXA)
• Participated in a resistance or aerobic training program in the last 3 months
• Engage in more than 1 hr/week of vigorous activity
• Body mass index >29
• On hormone replacement therapy