Muscle soreness is associated with enhancement of nitrogen oxide and DNA damage in human skeletal muscle

The mechanisms behind the muscle soreness are still poorly understood. The aim of the present investigation was to study the possible involvement of free radical species in muscle soreness. The presence of free radicals was measured directly by the determination of NO level using electron spin resonance (ESR) and indirectly by the measurement of DNA adduct of 8-hydroxydeoxyguanosine (8-OHdG) by ELISA method from human skeletal muscle. Fourteen physically active university students voluntarily participated in the study, and were divided into control (C) and exercised (E) group. The E group performed eccentric exercises in the gym and the biopsy samples were taken from the rectus femoris muscle one day after the exercising. The level of muscle soreness was evaluated by questionnaire scaled from zero to ten. The score ranged between 6 and 10 indicating significant muscle soreness at the time of biopsy sampling. There was a massive nearly three fold increase (P <0.0032) in NO level in the E group (0.96±0.05 arbitrary unit) compared with C group (0.39±0.08 arbitrary unit). The concentration of 8-OHdG was about 30% larger (P <0.05) in E group than in the muscle of C subjects. The results of the present study suggest that during muscle soreness there is a massive increase in NO production which is associated with the increase of DNA damage in human skeletal muscle.