Purpose: This study investigated the effect of downhill run-induced muscle damage on the recovery of strength and rate of velocity development (RVD) of the knee extensors. Methods: Twenty-two untrained men (22.0 ± 1.9 yrs) performed a 30-min DHR (downhill run; -17%) at the intensity of their pre-determined 70% maximal oxygen consumption (VO2max). Maximal isokinetic concentric strength (300°/s; concentric peak torque, CPT; RVD), delay-onset muscle soreness (DOMS) and plasma creatine kinase activity (CK) were measured before to 5 days after DHR. All data was analyzed by a one-way repeated measures ANOVA. Results: DOMS developed 1 day after DHR (p ＜ .05), peaked at 2 days (49 ± 25 mm) later, and returned to baseline (p ＜ .05) at 5 days after DHR. Plasma CK increased and peaked at 1 day (562 ± 284 IU/L; p ＜ .05) after DHR, but did not return baseline at 5 days after DHR (329 ± 277 IU/L). Immediately after DHR, CPT decreased to 17 ± 14% and then further slightly decrement of strength at 2 days (19 ± 4%) later, but returned to baseline at 5 days after DHR RVD significantly decreased to 44 ± 49% immediately after DHR, then further decreased at 2 days (50 ± 47%) later, but returned to pre-DHR level at 5 days after DHR. There was a negative correlation between peak DOMS and lowest RVD (r = -.72, p ＜ .05). Conclusion: These results suggested that RVD loss of the knee extensors in the days after DHR may be affected by the symptoms of DOMS, although strength loss and increased in CK after DHR may not directly contributed to changes in RVD. Future studies are warranted to explore how RVD loss affected by DOMS.
