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To examine the effect of repeated muscle-damaging exercise on the time-course changes in several indices of muscle damage, and to compare them with changes in blood oxidative stress indices.Twelve females underwent an isokinetic exercise session consisting of 75 lengthening knee flexions, which was repeated after 3 wk. Isometric torque, range of movement (ROM), delayed-onset muscle soreness (DOMS), creatine kinase (CK), reduced glutathione (GSH), oxidized glutathione (GSSG), thiobarbituric acid-reactive substances (TBARS), protein carbonyls, catalase, uric acid, bilirubin, and total antioxidant capacity (TAC) in blood were measured before, immediately after, and 1, 2, 3, 4, and 7 d after lengthening contractions.All muscle damage indices (torque, ROM, DOMS, and CK) changed significantly after exercise. The concentration of all oxidative stress indices changed significantly in a way indicating increased oxidative stress in the blood (GSH and GSH/GSSG decreased, whereas GSSG, TBARS, protein carbonyls, catalase, uric acid, bilirubin, and TAC increased), peaking in all but bilirubin at 3 d and returning to baseline values by 7 d after exercise. The repeated bout of lengthening contractions induced significantly less changes in indices of muscle damage and blood oxidative stress than the first bout. In general, from the increasing or decreasing area under the curve calculated for each oxidative stress index, the second bout produced 1.8- to 6.1-fold less changes in oxidative stress than after the first bout.A repeated bout of lengthening contractions attenuated muscle damage and blood oxidative stress compared with the first bout.