Eccentric exercise-induced delayed-onset muscle soreness and changes in markers of muscle damage and inflammation

The purpose of this study was to determine the relationships among delayed-onset muscle soreness (DOMS), muscle damage and inflammatory responses to eccentric exercise and investigate the underlying mechanisms. Nine healthy males performed one-leg calf-raise exercise with their right leg on a force plate. They performed 10 sets of 40 repetitions of exercise at 0.5 Hz by the load corresponding to the half of their body weight, with a rest for 3 min between sets. DOMS was evaluated by a visual analogue scale (VAS). Blood and urine samples were collected before and 2, 4, 24, 48, 72 and 96 h post-exercise. Blood samples were analyzed for leucocyte differential counts and neutrophil functions (migratory activity and oxidative burst activity). We also determined a serum marker of muscle damage, myoglobin (Mb), and plasma and urinary prostaglandin E2 as an algesic substance. As for the inflammatory mediators, plasma and urine were analyzed for cytokines (interleukin (IL)-1beta, IL-1 receptor antagonist, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12p40, IL-12p70, tumour necrosis factor-alpha, interferon-gamma, monocyte chemotactic protein-1, granulocyte colony-stimulating factor, macrophage colony-stimulating factor, and granulocyte macrophage colony-stimulating factor), leucocyte activation markers (calprotectin and myeloperoxidase), and neutrophil chemotactic factor complement 5a. All subjects reported muscle soreness on subsequent days and VAS peaked at 72 h after exercise. Serum Mb concentration significantly increased (p < 0.05) at 72 h after exercise as compared with the pre-exercise values which was correlated with the increases in VAS at 72 h (r = 0.73, p < 0.05). Circulating neutrophil count and migratory activity increased significantly (p < 0.01, and p < 0.05, respectively) at 4 h after exercise, whereas there were no significant changes in the other plasma and urinary inflammatory mediators. These results suggest that neutrophils can be mobilized into the circulation and migrate to the muscle tissue several hours after the eccentric exercise. There were also positive correlations between the exercise-induced increases in neutrophil migratory activity at 4 h and the increases in Mb at 48 h (r = 0.67, p < 0.05). These findings suggest that neutrophil mobilization and migration after exercise may be involved in the muscle damage and inflammatory processes.