The ENLIGHTEN PAD Trial will collect preliminary data to test whether daily 660 nm light treatment of the lower extremities immediately before home-based walking exercise sessions improves six-minute walk distance at 4-month follow-up, compared to sham light, in people with lower extremity peripheral artery disease (PAD).

The ENLIGHTEN PAD Trial will collect preliminary data to test whether daily 660 nm light treatment of the lower extremities immediately before home-based walking exercise sessions improves six-minute walk distance at 4-month follow-up, compared to sham light, in people with lower extremity peripheral artery disease (PAD) (Primary Aim #1). In Primary Aim #2, the investigators will measure the acute effect of the first treatment of 660 nm light on six-minute walk distance and on walking intensity (measured with the ActiGraph accelerometer) during the six-minute walk. In secondary and exploratory aims, the investigators will delineate biologic pathways by which 660 nm light enhances the benefits of home-based walking exercise, by measuring the effects of 660 nm light on exercise intensity during the exercise intervention and by measuring the effects of 660 nm light on plasma nitrosothiols, leg perfusion, and gastrocnemius muscle health and mitochondrial activity. Exercise intensity will be measured by the well validated ActiGraph accelerometer.

The ENLIGHTEN PAD Trial is a Phase II multi-centered randomized clinical trial. Thirty-two participants with PAD will be randomized at one of two centers: Northwestern University (PI: MM McDermott, MD) and the University of Alabama (PI: Nicole Lohr MD, PhD) to either 660 nm light + home-based exercise or sham light + home-based exercise for four months. Both groups of participants will receive the same home-based high intensity walking exercise intervention.

Inclusion Criteria:

First, all participants will be age 50 and older. Second, all participants will have PAD. PAD will be defined as:

1. An ABI <= 0.90 at baseline.
2. Vascular lab evidence of PAD (such as a toe brachial pressure <= 0.70 or an ankle brachial index less than or equal to 0.90), or angiographic evidence of PAD defined as at least 70% stenosis of an artery supplying the lower extremities.
3. An ABI of >0.90 and <= 1.00 who experience a 20% or greater drop in ABI in either leg after the heel-rise test.

Exclusion Criteria:

1. Above- or below-knee amputation
2. Critical limb ischemia defined as an ABI <0.40 with symptoms of rest pain
3. Wheelchair confinement or requiring a walker to ambulate
4. Walking is limited by a symptom other than PAD
5. Current foot ulcer on bottom of foot
6. Failure to successfully complete the study run-in
7. Planned major surgery, coronary or leg revascularization during the next four months
8. Major surgery, coronary or leg revascularization or major cardiovascular event in the previous three months
9. Major medical illness including lung disease requiring oxygen, Parkinson's disease, a life-threatening illness with life expectancy less than six months, or cancer requiring treatment in the previous two years. [NOTE: potential participants may still qualify if they have had treatment for an early stage cancer in the past two years and the prognosis is excellent, unless the cancer is located in the lower extremities. Participants who require oxygen only at night may still qualify.]
10. Mini-Mental Status Examination (MMSE) score < 23
11. Non-English speaking
12. Participation in or completion of a clinical trial in the previous three months. [NOTE: after completing a stem cell or gene therapy intervention, participants will become eligible after the final study follow-up visit of the stem cell or gene therapy study so long as at least six months have passed since the final intervention administration. After completing a supplement or drug therapy (other than stem cell or gene therapy), participants will be eligible after the final study follow-up visit as long as at least three months have passed since the final intervention of the trial.]
13. Visual impairment that limits walking ability.
14. Six-minute walk distance of <400 feet or >1700 feet.
15. Participation in a supervised treadmill exercise program or a cardiac rehabilitation program in previous three months or planning to begin a supervised treadmill exercise program or a cardiac rehabilitation program in the next five months.
16. Unwilling to avoid red light therapy outside of study participation.
17. Baseline blood pressure <100/45.
18. In addition to the above criteria, investigator discretion will be used to determine if the trial is unsafe or not a good fit for the potential participant.

This will be a double blinded study where both the participant and the people collecting data will be blinded.