Chapman, DW, Newton, MJ, McGuigan, MR, and Nosaka, K. Effect of slow-velocity lengthening contractions on muscle damage induced by fast-velocity lengthening contractions. J Strength Cond Res 25(1): 211-219, 2011-This study tested the hypothesis that the first exercise bout consisting of slow-velocity (30°·s−1) maximal lengthening contractions would not affect muscle damage in a subsequent bout consisting of fast-velocity (210°·s−1) lengthening contractions. Eighteen men were randomly assigned into either a repeated bout group (n = 10) or control group (n = 8). The repeated bout group performed 2 bouts of exercise consisting of 210 maximal lengthening contractions of the elbow flexors separated by 14 days at a velocity of 30°·s−1 for the first and 210°·s−1 for the second bout. The control group performed a single bout of the fast-velocity exercise. Changes in maximal isometric strength, range of motion (ROM), upper-arm circumference, muscle thickness, muscle soreness, serum creatine kinase, and lactate dehydrogenase activities were measured before, immediately after, and 24 to 96 hours after exercise. The repeated bout group showed significantly (p < 0.05) smaller changes in all criterion measures except for muscle soreness after the fast-velocity exercise compared with the control group. A significant (p < 0.05) difference was evident only for ROM between the slow- and fast-velocity bouts of the repeated bout group. These results suggest that slow-velocity exercise reduced muscle damage induced by fast-velocity exercise, although the reduction was not large.