Effect of linear polarized near-infrared light irradiation on muscle fatigue recovery after repeated handgrip exercise.

Linear polarized near-infrared light (PL) irradiation is considered one of the useful methods for muscle fatigue recovery, because it increases the blood flow and skin temperature of the irradiated part. The purpose of this study was to examine the effect of PL-irradiation on muscle fatigue recovery and physiological response in the upper limbs after maximal repeated rhythmic hand gripping (RRH). Ten males and ten females participated in this study. Subjects performed RRH for 9 min, and then rested for 20 min with PL- or placebo-irradiations. After rest, they again performed RRH for 3 min. As evaluation parameters, we selected the sustained force curve during RRH, subjective muscle-fatigue sensation (Fs), blood lactate concentration (La), muscle oxygenation (Total Hb, Oxy-Hb, and Deoxy-Hb), and skin temperature. The decreasing rate of the integrated area for 30 sec during RRH was significantly smaller in the PL-irradiation than with the placebo. There were no significant differences between irradiation conditions for fatigue sensation and lactate concentration skin temperature during rest was kept high by PL-irradiation. Muscle oxygenation tended to remain slightly high during the initial phase (1-8 min after the exercise). It is inferred that PL-irradiation maintains a high skin temperature and blood flow, but it may not contribute to recover muscle contraction performance in muscle fatigue.