Establishment of an animal model for delayed-onset muscle soreness after high-intensity eccentric exercise and its application for investigating the efficacy of low-load eccentric training

Delayed-onset muscle soreness (DOMS) occurs after unaccustomed exercise and is particularly associated with eccentric exercise. Previous studies have proposed the use of a single bout of eccentric exercise to prevent the muscle damage subsequent to a bout of eccentric exercise. This study aimed to establish a suitable animal model to evaluate the pain in DOMS and to assess whether low-load eccentric training confers a protective effect against a subsequent high-intensity eccentric exercise bout. Thirty-six female Wistar rats were divided into five groups: rats that received muscular compression only (Comp); those that received high-intensity eccentric exercise only (HE); those that received muscular compression at 3, 24, 48, and 96 h after high-intensity eccentric exercise (HE + Comp/3, 24, 48, and 96 h); those that received muscular compression 48 h after a single low-load eccentric exercise (LE); and those that received a week of low-load eccentric training before high-intensity eccentric exercise, which was followed by muscular compression 48 h later (LET). Immunohistochemistry was used to investigate c-fos expression in the dorsal horn of the spinal cord. For the HE + Comp/48 h rats, the total number of c-fos-positive neurons at the L2-3 segments was significantly greater than that in the Comp and HE rats in the same segments. A week of low-load eccentric training resulted in a decreased number of c-fos-ir neurons relative to that in the HE + Comp/48 h rats. Muscle tenderness after high-intensity eccentric exercise was evaluated by c-fos expression in the dorsal horn of the rat spinal cord. Using this rat model, the present study clarified that the muscle tenderness following high-intensity eccentric exercise is inhibited by prior low-load eccentric training.