Therapeutic Effect Of Low Intensity Laser Irradiation On Exercise-induced Muscle Damage And Its Mechanism

Exercise-induced muscle damage (EIMD) is referred to the micro-damage of skeletal muscle induced by an unaccustomed, especially high-intensity and eccentric exercise. Human EIMD is also named as delayed onset muscle soreness (DOMS) because the patient with EIMD experienced delayed onset soreness in muscle after exercise. DOMS is a common phenomenon in sports training and so far no really efficient therapeutic approach has been found. Low intensity laser therapy (LLLT) may be an important treatment for DOMS, but the efficacy is uncertain and the mechanism behind the beneficial clinic effects is unclear.In this study, the effects of low intensity He-Ne laser irradiation at different doses on eccentric exercise-induced muscle injury and its mechanism were investigated with animal experimental method first time. Seventy-two Sprague-Dawley rats were randomly divided into five groups: (1) sedentary control group; (2) exercise control group; (3) three exercise plus laser groups: low-dose laser group, medium-dose laser group, and high-dose laser group. Each of the four exercise groups was further divided into two subgroups: 24 h post-exercise subgroup and 48 h post-exercise subgroup. The exercise was a bout of downhill running (gradient at -16°, speed at 16 m/min) to exhaustion. The laser irradiation was done immediately, 18 h and 42 h after exercise at the middle bellies of bilateral gastrocnemius muscles with He-Ne laser at 12, 28, and 43 J/cm~2(20, 46, and 71 mW/cm~2, 10 min), respectively. At 24 and 48 h after exercise, the gastrocnemius muscles and blood were sampled. Histological change in muscle was examined by HE staining method, and muscle desmin was was examined by immuno-histochemistry staining method, and the analysis for serum creatine kinase (CK), muscle superoxide dismutase (SOD), malondiadehyde (MDA), nitric oxide synthase (NOS) and nitric oxide (NO) were done by biochemistry method.Main results were as following:(1) The exercise control group exhibited a few myofibers undergoing necrosis, a marked inflammation in the gastrocnemius muscle 24 and 48 h after exercise. There were significant elevations in serum CK activity, muscle MDA level and NOS activity, and a significant decrease in muscle desmin over sedentary control level in the same post-exercise periods. In addition, there were also obvious reductions in the ratios of SOD/MDA and NO/MDA after exercise, which were more obvious at 24 h after exercise, whereas the muscle inflammation and the elevation of serum CK activity were more obvious at 48 h after exercise.(2) He-Ne irradiation at 43 J/cm~2 obviously reduced the amount of necrotic myofibers, inhibiting muscle inflammation, and significantly reduced the extent of elevation in serum CK activity and the loss of muscle desmin at both 24 and 48 h after exercise. The irradiation at 43 J/cm~2 also significantly enhanced muscle SOD activity, lowering muscle MDA level, and significantly enhanced muscle NOS activity and NO level so that the ratios of SOD/MDA and NO/MDA obviously increased as compared to the exercise control group in the same post-exercise periods. There were no significant differences in the serum CK activity and muscle MDA level between the laser group receiving 43 J/cm~2 and the sedentary control group at both 24 h and 48 h after exercise.(3) He-Ne irradiation at 12 or 28 J/cm~2 significantly reduced the loss of muscle desmin and partly inhibited muscle inflammation at both 24 and 48 h after exercise, and significantly inhibited serum CK activity only at 48 h after exercise. The effects of the irradiation at 12 or 28 J/cm~2 on other outcomes were no sigmificant.Conclusion:(1) The imbalance between reactive nitric species and reactive oxygen species is involved in the development of eccentric exercise-induced muscle injury in rats.(2) Low intensity He-Ne laser could efficiently reduce eccentric exercise-induced muscle injury in rats and promote the repair of tissue through inhibiting muscle inflammation and restoring the balance between oxidation and anti-oxidation and the balance between reactive nitric species and reactive oxygen species in muscle in time.(3) The effects of low intensity He-Ne laser on eccentric exercise-induced muscle injury in rats depend on laser intensity and dose, and the dose 43 J/cm~2 (71 mW/cm~2, 10 min) is the most efficient among the doses used.