SCHWANE, J.A., J. S. WILLIAMS, and J. H. SLOAN. Effects of training on delayed muscle soreness and serum creatine kinase activity after running.Med. Sci. Sports Exerc., Vol. 19, No. 6, pp. 584–590, 1987. We studied the effects of progressive, short-term training on the delayed muscle soreness (DMS) and serum creatine kinase (SCK) responses to downhill (-10%) running for 45 min. Prior to the experimental run, subjects in training groups (N= 38) ran for 5 min to 15 min·d-1on either −10% or +10% incline for either 1 wk (5 d) or 2 wk (10 d). Twelve control subjects did not train. DMS was reduced, although not totally prevented, by the 1 wk, and especially, 2 wk of downhill running training. Training by uphill running had little effect in preventing DMS. Mean SCK values 24 h after the experimental run were not significantly different among the groups (range: 99 to 340% of pre-exercise values), indicating no effect of any training regimen. Relatively large differences existed among subjects in terms of soreness and SCK responses to the experimental running. It was suggested that DMS may be difficult to totally avoid if exercise with a large eccentric component is performed. Prevention of such DMS may be most likely if prior training involves exercise with a substantial eccentric component, starts with bouts of very small quantities, and progresses in small increments over more than 2 wk.