Chronic Effect Of Photobiomodulation Therapy On Muscle Function In Persons With Multiple Sclerosis

Muscle weakness and fatigue are two disabling symptoms of Multiple Sclerosis (MS). Photobiomodulation therapy (PBMT) using red/near-infrared light is an emerging therapeutic modality thought to improve endurance or strength in healthy populations. Previously presented work revealed that a single acute high energy dose of PBMT may improve muscle force recovery in persons with MS (PwMS). PURPOSE: To investigate the effect of extended PBMT at an optimal dose of energy on muscle strength and endurance during a fatiguing contraction in PwMS. METHODS: Randomized crossover design. Persons with mild-moderate relapsing-remitting MS (n = 12, F = 11) were recruited. Participants applied PBMT (active or placebo) to the gastrocnemius and Tibialis Anterior (TA) muscles of both legs twice a day. The optimal dose of energy of the active device for each participant was 40 J, 80 J, or 120 J as determined individually from preliminary studies. The effect of PBMT on muscle function was assessed in five sessions, pre- and post-treatment, and post-washout. The measurements comprised three maximal voluntary contractions (MVCs) of the right TA, followed by an intermittent contraction at 50% MVC to task failure. The measurements were obtained at baseline, after which followed two weeks of active or placebo treatment at home, followed by post-treatment measurements. Then participants had two weeks with no intervention or placebo to wash-off any potential effects, followed by the repetition of the procedure with the other active or placebo device, again followed by two weeks of washout. The Wilcoxon signed-rank test was used to compare the change in pre to post-treatment measurement within subjects and between the active treatment and placebo. Values are mean (SD) in N. RESULTS: Under active treatment, strength significantly improved compared to the baseline (Pre,162.64 (37.51); Post,185.56 (33.95), p = 0.01) and compared to the placebo (Active,22.64 (24.01); Placebo,-4.12 (32.24), p = 0.02). No significant difference in strength was reported with placebo (p = 0.68). Endurance time did not change significantly with either active treatment (p = 0.52) nor placebo (p = 0.85). CONCLUSIONS: Two-week administration of PBMT may improve muscle strength in persons with mild-moderate MS. Supported by a pilot grant from the National MS Society.