|（1.Lab of Laser Sports Medicine，South China Normal University，Guangzhou 510006，China；2. Institute of Biomedical Photonics，Huazhong University of Science and Technology，Wuhan 430074，China）
Abstract: This study has investigated the effects of low-level He-Ne laser irradiation at different doses on the me-tabolism of free radicals and nitric oxide (NO) of rat skeletal muscle after exhaustive exercise by using the animal model of downhill running. Seventy-two Sprague-Dawley rats were randomly divided into five groups: sedentary control group, exercise control group，exercise + low-dose laser group, exercise + medium-dose laser group, and exercise + high-dose laser group. Each rat in the exercise control group and the three exercise plus laser groups per-formed a bout of exhaustive downhill running on treadmill. Three exercise plus laser groups received He-Ne laser irradiation after exercise at gastrocnemius muscles daily. The irradiation parameters for three different dose laser groups were 12, 28, and 43 J/cm2（20, 46, and 71 mW/cm2，10 min）, respectively. Gastrocnemius muscles were sampled at 24 and 48 h after exercise. Muscle superoxide dismutase (SOD), malondiadehyde (MDA), nitric oxide synthase (NOS) and NO were analyzed. The exercise control group exhibited significant elevations in muscle MDA level and NOS activity after exhaustive exercise. He-Ne laser irradiation at 43 J/cm2 significantly enhanced muscle SOD activity, NOS activity and NO level and significantly reduced muscle MDA level after exercise, whereas the effects of the irradiation at 12 or 28 J/cm2 were unmarked. In conclusion, low-level laser irradiation could enhance muscle anti-oxidative capacity and reduce free radicals level, and promote to synthesize NO and increase NO level in a dose/intensity-dependent manner.
Key words: exercise biochemistry；low-level laser；photobiomodulation；free radical；nitric oxide；exhaustive exercise