This study will test whether photobiomodulation therapy improves muscle endurance and decreases inflammation in persons with relapsing-remitting multiple sclerosis. We will also investigate mechanisms for any improvements.

Persons with multiple sclerosis (MS) MS commonly experience muscle weakness and fatigue which may contribute to the commonly reported symptomatic fatigue. Photobiomodulation therapy (PBMT) induced with light in the visible red to near infrared (VIS/NIR) region of the spectrum (600-1000 nm) can stimulate cytochrome c oxidase and improve mitochondrial function. PBMT is an emerging therapeutic modality for soft tissue injury, chronic inflammation, neurodegeneration , and retinal diseases. PBMT has also been used to enhance muscle endurance, strength and recovery in healthy adults. We propose that in persons with MS, PBMT will 1) enhance regional muscle endurance after acute treatment and 2) enhance functional endurance after extended treatment. We will also test to determine if improvements are due to central or peripheral neuromuscular or cardiovascular mechanisms. Final, we will explore if regional PBMT can result in systemic anti-inflammatory effects.

Inclusion Criteria:

1. Relapsing remitting MS,
2. Independent or ambulatory with minimal aid.
3. Must be able to move foot (ankle dorsiflexion) at least moderately forcibly against gravity (manual muscle test score 3-5)
4. Subjects must be able to walk for 6 minutes independently with no or minimal use of an assistive device.

Exclusion Criteria:

1. No noticeable left right ankle strength asymmetry
2. No exacerbations (MS attacks) or immunosuppressive therapy use within the previous 6 months
3. No concurrent infection or known cardiovascular disease including having a pacemaker; or other serious medical co-morbidity including metabolic, mitochondrial, autoimmune, diseases or other co-existing neurologic conditions.
4. Not involved in any clinical trial or other research that could confound results.
5. Must not be pregnant
6. Must not have an active diagnosis of cancer