BACKGROUND: LED phototherapy can attenuate muscle fatigue and accelerate muscle recovery in young persons, but little is known about photobiomodulation effects on muscle strength in the elderly. OBJECTIVE: To assess the effects of LED phototherapy on the grip strength and muscle fatigue of wrist flexors in elderly women. METHODS: Twenty-nine women were recruited and allocated to placebo group (PG) (n = 14) and LED group (LG) (n = 15). Grip strength, number of resisted wrist flexion repetitions, and serum creatine kinase (CK) were measured. The subjects were irradiated with one diode (638 nm, 150 mW, 11.7 J/cm2, 4.5 J/point) at four points on the wrist flexor muscles, and fatigue was induced by exercise using 75% of one maximum repetition (1MR). When muscle fatigue was reached, grip strength and CK were reassessed. RESULTS: In the LG, there was no intra-group difference for grip strength (N), 217.7 +/- 34.3 to 209.9 +/- 35.3 (p = 0.063) whereas in the PG, there was decrease in strength from 203.0 +/- 22.5 to 181.4 +/- 21.6 (p < 0.001). LED increased the number of repetitions by 22.0%. An increase in CK (U/L) was observed in PG in all post-fatigue periods (p = 0.003) but no difference was found in the LG (p = 0.972). CONCLUSIONS: A single application of LED before muscle fatigue induction may effectively maintain grip strength and reduce muscle fatigue and damage.

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