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This study investigated the effect of lengthening contraction velocity on exercise-induced muscle damage.Sixteen men were placed into two groups performing either 30 (N = 8) or 210 (N = 8) maximal lengthening contractions of the elbow flexors on an isokinetic dynamometer. Dominant and nondominant arms were randomly assigned for a slow-velocity (S: 30°·s−1) or a fast-velocity (F: 210°·s−1) exercise separated by 14 d. Maximal voluntary strength of isometric contractions (iMVC) and isokinetic concentric contractions (cMVC), range of motion (ROM), upper-arm circumference, muscle soreness, and serum creatine kinase (CK) activity were measured before, immediately after, and 1-120 h after exercise. Changes in these measures over time were compared by a two-way repeated-measures ANOVA to examine the effect of velocity in the same number of contractions (S30 vs F30; S210 vs F210) or the effect of contraction number at the same velocity (S30 vs S210; F30 vs F210).A significant (P < 0.05) interaction effect was evident only for iMVC between S30 and F30, but it was evident for iMVC, cMVC, ROM, and CK between S210 and F210. Changes in most of the measures were significantly (P < 0.05) smaller after 30 contractions (S30 and F30) than after 210 contractions (S210 and F210).These results suggest that the effect of contraction velocity on the magnitude of muscle damage after 30 contractions is minor; however, when 210 lengthening contractions were performed, the effect of contraction velocity became conspicuous. It is concluded that fast-velocity lengthening contractions are likely to induce greater muscle damage than slow-velocity contractions; however, muscle fatigue seems to be a confounding factor for the velocity effect.