Photobiomodulation time response of human skeletal muscle fatigue
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Photobiomodulation therapy (PBMT) is a modality that is gaining popularity in the sports medicine field. By using light, specifically red and infrared wavelengths, PBMT can reduce inflammation, promote faster healing and recovery, treat neurological disorders and pain, and also prevent muscle damage following intense exercise. More recently, it has been shown that PBMT can also increase resistance to skeletal muscle fatigue by stimulating mitochondrial function in muscle cells. Photobiomodulation therapy improves ATP production in the cell for up to 24 hours post-irradiation. The purpose of this study was to determine the optimal time between PBMT application and a knee extensor exercise to resist fatigue. A total of 42 participants were randomized into 4 different treatment groups: (1) PBMT applied 0 h (<10 minutes) prior to exercise, (2) PBMT applied 5 h prior to exercise, (3) PBMT applied 24 h prior to exercise, and (4) sham PBMT at 0 h, 5 h, or 24 h prior to exercise. The sham treatment was with the same device, just not powered on. This study aimed to demonstrate that 5 hours prior to an exercise rather than immediately before will give the muscle the greatest resistance to fatigue. Peak quadriceps torque pre-fatigue to post-fatigue task (MVC), muscle fatigue, and acute muscle soreness perception (mVAS) were measured. None of the PBMT groups were able to reduce fatigue in any outcome measure. Although the results were not significant (P = 0.2488), the PBMT 0 h and 5 h treatment groups showed smaller decreases in peak quad torque compared to the sham treatment. The 5 h PBMT group also had slightly better muscle endurance during the fatigue test, averaging 4% more repetitions than the 0 h treatment (P = 0.9169). The results hint that PBMT application 5 hours before a fatiguing exercise may enhance muscular endurance and prevent a decrease in maximal strength compared to an immediate application, however further investigation is necessary.