The Effect of Low-Level Laser Therapy on Electrically Induced Muscle Fatigue: A Pilot Study

Abstract

The purpose of this pilot study is to determine if low-level laser therapy (LLLT) could attenuate skeletal muscle fatigue induced by surface neuromuscular electrical stimulation (NMES) in healthy volunteers. Five college-age participants underwent three cross-over randomized trials: two (LLLT + NMES) test trials and a control trial (NMES only), in which NMES was applied to their dominant knee extensor muscle group. The LLLT doses, 500 mW at 808 nm, were either adjusted to deliver a total energy of 7 J for 10 min or 3 J for 5 min in a blinded fashion. Following LLLT irradiation, the NMES protocol was immediately delivered for 3 min to induce fatigue in the knee extensor muscle group. The five participants completed the three trials. After the control trial, torque significantly decreased (62%; p < 0.0001) at the end of 3 min. There was no significant difference between the 7 J and 3 J trials on muscle fatigue. Following both LLLT trials, torque significantly decreased (51%; p < 0.0001) at the end of 3 min. Although there was a difference (11%) in fatigue between the two LLLT trials and the control trial, this difference did not attain statistical significance (p = 0.63). LLLT did not attenuate muscle fatigue evoked by NMES, but this needs to be further addressed in human studies and clinical settings. The lack of significant findings could be explained by the small sample size and the selection of LLLT parameters.