Author(s): IDE, D.1, YAMADA, K.1, MATSUDAIRA, H.1, MIYAZAKI, M.2, ITOH, H.1, Institution: NAGOYA INSTITUTION OF TECHNOLOGY , Country: JAPAN, Abstract-ID: 784

INTRODUCTION:
Muscle damage-induced reduction in force generation is accompanied by increased nitric oxide (NO) content in human skeletal muscle (Radák et al. 1999). We (Ohkuwa et al. 2006) previously have been detected NO emanating from human skin (skin-gas), however, there is very little data concerning with skin-gas NO concentration on the surface of damaged muscle in human. Therefore, we examined whether skin-gas NO would be as a marker of damaging muscle inflammation or not.
METHODS:
Seven healthy male students (22.1 ± 0.3 years; mean ± SD) volunteered as the subjects. None of them had performed muscle- damaging exercise at least six months prior to the experiment. The subjects performed 8 sets of 15 repetition-maximum (RM) knee flexion-extension exercise (left leg only) consisting of predominantly isokinetic eccentric contractions. The skin-gas samples were obtained from the surface of the belly muscle of the rectus femoris before exercise and 1, 2, 3, 7 days after exercise. The skin-gas NO concentration was measured by a chemiluminescence analyzer (Pico-Device Co., Ltd., Nagoya, Japan). Knee extension muscle strength (1RM), circumference of the thigh, muscle soreness (visual analog scale; VAS) of exercised left leg, and serum nitrites, creatine kinase activity were also measured.
RESULTS:
The skin-gas NO concentration significantly increased 2 days after the exercise compared to pre-exercise values (p<0.01) and returned to pre-exercise levels 7 days after exercise. The peak skin-gas NO concentration (16.1 ± 0.6 ppb) of each subject was about 1.4 times more than pre-exercise value (11.8 ± 0.9 ppb). Although no significant difference was found in the circumference of the exercised thigh during experimental period, muscle strength significantly (p<0.05) decreased, and VAS significantly (p<0.05) increased compared to the pre-exercise values 1-3 days after exercise. Serum CK activity increased significantly at 3 days after exercise compared to pre-exercise values (p<0.05) and returned to pre-exercise levels 7 days after exercise. Serum nitrate concentration also significantly (p<0.01) increased 2 days after the exercise compared to pre-exercise values.
CONCLUSION:
Eccentric exercise induces mechanical muscle damages and pathological changes such as fiber necrosis and inflammatory cell infiltration that become apparent a few days later (Maruhashi et al. 2007). It is known that delayed reactive oxygen species (ROS) production to inflammatory reactions induced in damaged muscle (Close et al. 2004). Therefore, increased skin-gas NO concentrations in this study may be due to activation of induced NO synthase in the damaged muscle cells or in activated macrophages.Exercise-induced muscle damage increases skin-gas NO concentrations, and skin-gas NO concentrations on the surface of damaged muscle may be a useful index for determining decreasing muscle strength and muscleinflammation