The overall goal of observational study is to examine the age-related and habitual exercise training status-related differences in structural and functional changes in the human brain, detected by magnetic resonance (MR) imaging.

Normal aging reduces cerebral blood flow, brain volume, and cognitive function, thereby increasing the risk of dementia or Alzheimer's disease. Aging is associated with increased white matter hyperintensities (WMH) and appears to alter functional connectivity within the brain both of which associated with cognitive function (references). Observational studies suggest that regular physical activity is associated with improved cognitive function and higher cerebral blood flow 1,2. However, it is unknown if aging or exercise training status alters the structural and functional biomarkers that are predictive of cognitive decline. Thus, the overall goal of this project is to examine the age-related and exercise training status-related differences in structural and functional changes in the brain, detected by magnetic resonance (MR) imaging.

1. To determine if white matter hyperintensities on MRI scans of the brain are altered by aging and exercise training status.
2. To determine the interaction of aging and habitual physical activity on functional connectivity in the brain.

Inclusion Criteria:

• Between 18-35 or 55-75
• Body mass index <34 kg/m2
• Physically active (exercise more than 3 times per week for at least 30 min) or sedentary (no formal exercise over 1 hour per week)

Exclusion Criteria:

• Current smoker
• History or evidence of: hepatic disease, renal disease, hematological disease, peripheral vascular disease, stroke/neurovascular disease, diabetes, hypertension
• Part of a vulnerable population (e.g. pregnant women, prisoner, individuals lacking capacity to consent, etc.)

Subjects for this study will include healthy young adults (18-35 years old), sedentary older adults (55-75 years old), and healthy exercise trained older adults (55-75 years old). Both men and women will be eligible to participate in this study.