Effect of 808 nm low-level laser therapy in exercise-induced skeletal muscle fatigue in elderly women

Aging process involves several structural changes in muscle tissue which lead to decrease in musculoskeletal function. One of the most common physiological modifications is the increase in fatigability in elderly people, which leads to inability to maintain strength and motor control. In this context, low-level laser therapy (LLLT) has demonstrated positive results in reducing fatigue during physical exercise. Thus, this study aimed to investigate the effects of LLLT on skeletal muscle fatigue in elderly women. Twenty-four subjects divided in two groups entered a crossover randomized triple-blinded placebo-controlled trial. Active LLLT (808 nm wavelength, 100 mW, energy 7 J) or an identical placebo LLLT was delivered on the rectus femoris muscle immediately before a fatigue protocol. Subjects performed a fatigue protocol which consisted of voluntary isotonic contractions of knee flexion–extension performed with a load corresponding to 75 % of 1-MR (Maximum Repetition) during 60 s. Surface electromyography (SEMG) signals were recorded from rectus femoris muscle of dominant lower limb to evaluate peripheral fatigability using median frequency analysis of SEMG signal. The number of repetitions of flexion–extension during fatigue protocol was also compared between groups. The values of median frequency were used to calculate the slope coefficient. The results showed no difference in the slope comparing placebo LLLT and active LLLT groups (p = 0.293). However, a significant difference was observed in the number of repetitions between groups, after active LLLT, subjects demonstrated significantly higher number of repetitions (p = 0.047). In this study, LLLT was efficient in increasing the mean number of repetitions during knee flexion–extension exercise, although results have not shown delay electromyographic fatigue.