Acute Photobiomodulation by LED Does Not Alter Muscle Fatigue and Cycling Performance.

PURPOSE: The purpose of the present study was to investigate the ergogenic effects of two doses of photobiomodulation therapy (PBMT) in comparison to placebo on markers of respiratory and muscle activity, blood acid-base, ion and lactate concentrations, indicators of muscle fatigue (global, central, and peripheral), and time to exhaustion in severe-intensity cycling. METHODS: Two separate studies were performed, both in a pseudorandomized and balanced, crossover design. In Study 1, fourteen male recreational cyclists completed three constant-load severe-intensity cycling bouts with duration-matched. The PBMT (18x38 cm array with 200 diodes) treatments occurred before bouts at 260 J, 130 J, or 0 J (placebo) doses. Electromyographic activity (EMG) of selected lower limb musculature was assessed during each bout. Maximal voluntary contractions of knee extension with peripheral nerve stimulations and EMG activity evaluation of vastus lateralis was also performed before and after cycling. In Study 2, thirteen recreational cyclists performed three bouts of constant-load severe-intensity cycling until exhaustion, preceded by PBMT as detailed above. Blood lactate concentrations, respiratory responses, EMG activity and capillary gasometry aspects were monitored. RESULTS: In both studies, there were no interactions effects (time×condition) on the EMG activity, which was displayed as root mean square (P≥0.168) and median frequency (P≥0.055) during cycling. In Study 1, there were no interaction effects on the indicators of muscle fatigue after exercise (P≥0.130). In Study 2, there were no differences on time to exhaustion (P=0.353) and no interaction effects among the physiological responses monitored (P≥0.082). CONCLUSIONS: Based on our findings, the PBMT at 260 J and 130 J doses does not have a beneficial effect on muscle fatigue, cycling performance, metabolic parameters and muscle activity in male recreational cyclists.