Peripheral arterial disease (PAD) is a disease in which fatty build-up, or "plaque," accumulates in the peripheral arteries. People with PAD often experience leg pain while walking due to reduced blood flow to the legs. This study will use magnetic resonance imaging (MRI) techniques to examine how specific features of plaque build-up in the leg arteries affect walking ability, leg strength, and balance in people with PAD.

Plaque build-up caused by atherosclerosis increases the risk of blood clots, heart attack, and stroke. Blockages of plaque can occur in different areas of the body. PAD, a circulatory disorder in which blockages occur in the peripheral arteries, is one manifestation of atherosclerosis. Individuals with PAD experience reduced blood flow to the legs, which may cause leg pain while walking. This study will use MRI techniques to examine how characteristics of plaque build-up in the leg arteries change over time and how this change affects function, walking ability, leg strength, and balance in people with PAD. Results from this study may be used to shape future research studies that will attempt to identify more effective treatments for people with PAD.

This study will enroll people with PAD, as well as a smaller control group of people who do not have PAD. At an initial study visit, study researchers will interview participants to collect information about their medical history, daily activity level, walking ability, and mental functioning. Blood collection and a leg MRI will occur. Also, blood flow to the legs will be measured by comparing blood pressure measurements in the arms and legs. Leg function will be measured through a series of timed walks, leg strength exercises, and muscle power exercises. Questionnaires to assess participants' medical history will be completed by each participant's primary care doctor, and study researchers will review participants' medical records. Participants with knee pain will have a knee x-ray, and participants may wear a small device called an accelerometer for 1 week to monitor physical activity levels. During the second and third study visits, occurring at one and two year follow-up, blood flow, leg function, and leg strength will be measured. If participants cannot attend either study visit, researchers may visit participants at their home or conduct an interview over the phone. Study researchers may contact participants by phone once or twice a year for follow-up.

Inclusion Criteria:

• For participants with PAD: lowest leg ankle-brachial index (ABI) less than or equal to 0.999
• For participants in the control group: lowest ABI between 1.00 to 1.30

Exclusion Criteria:

• Foot amputation, leg amputation, or gangrene
• Recent liver transplantation
• Requires oxygen on ambulation
• End stage renal disease
• Confined to a wheelchair
• Lives in a nursing home
• Low life expectancy
• Mini-Mental Status Exam (MMSE) score of less than 23 out of 30
• Communication difficulty due to language barriers
• Inability to tolerate MRI testing for any reason
• Six-minute walk performance limited primarily by pulmonary disease, legal blindness, or severe lower extremity arthritis

Ankle Brachial Index less than 1 in participants