Background Delayed onset muscle soreness (DOMS) occurs after unaccustomed exercise and is particularly associated with high-intensity eccentric exercise. Eccentric exercise is reported to have a protective effect against DOMS caused by subsequent eccentric exercise. Since objective assessment of pain is difficult, only limited experimental studies on DOMS and a few studies on pain prevention in DOMS have been performed.

Objective To examine the hypothesis that performing a low-load eccentric exercise before the high-intensity exercise could reduce the pain associated with DOMS.

Design Experimental study.

Interventions 36 male Wistar rats were divided into five groups: rats that received muscular compression only (Comp); those that performed high-intensity eccentric exercise only (HE); those that received muscular compression 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 underwent a week of low-load eccentric training before starting high-intensity eccentric exercise, which was followed by muscular compression 48 h later (LET).

Main outcome measurements Immunohistochemistry was used to determine c-fos expression in the spinal dorsal horn, and change in the tenderness of the exercised muscle was determined from c-fos expression.

Results In the HE+Comp/48 h rats, the total number of c-fos-positive neurons at the L2 segment was significantly greater than that at the L2 segment in the Comp and HE rats. A week of low-load eccentric training resulted in a decreased number of c-fos-positive neurons compared with the HE+Comp/48 h rats.

Conclusions The increase in c-fos-positive neurons in the dorsal horn indicated the presence of muscle tenderness. Our data suggest that muscle tenderness occurs in muscles for which high-intensity eccentric exercise has been applied 48 h ago; this tenderness is reduced when low-load eccentric training is performed before high-intensity eccentric exercise.