Changes in indicators of inflammation after eccentric exercise of the elbow flexors

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Abstract
This study examined muscle swelling and changes in inflammatory markers in the blood following eccentric exercise-induced muscle damage. Subjects(N = 14) who had not been involved in a resistance training program performed 24 maximal eccentric actions of the elbow flexors. Muscle swelling was assessed by measures of the upper arm circumference (CIR), ultrasonography(USG), and magnetic resonance imaging (MRI). Plasma concentrations of interleukin-1α, interleukin-1β, interleukin-2, interleukin-6, tumor necrosis factor-α, and plasma levels of C-reactive protein, cortisol, and zinc were analyzed. Established indicators of muscle damage (maximal isometric force, range of motion, muscle soreness, and plasma creatine kinase, aspartate aminotransferase, and lactate dehydrogenase activities) were also measured. All measures, including CIR and USG, except for MRI, were assessed immediately before and after and for 5 d post-exercise. MRI was taken at pre- and 1, 3, 6, 10, 23, 31, and 58 d post-exercise. All muscle damage indicators changed significantly after exercise. A large increase in CIR (>20 mm) was found 4-5 d after exercise, and this coincided with USG, showing an increase in muscle thickness. The echointensity of USG increased with the enlargement of the elbow flexors. MRI displayed enlargement of the biceps brachii and brachialis cross-sectional area that started at 1 d, and lasted until 23 d, post-exercise. The most profound increase in the enlargement and signal intensity of the MRI was found 3 or 6 d after exercise. However, none of the plasma levels of inflammatory makers showed significant changes. It is concluded that exercise-induced muscle damage caused muscle swelling, which is indicative of muscle edema, but the inflammatory responses after exercise appear to be different from those accompanying infection or tissue injury.