Cyclic eccentric stretching induces more damage and improved subsequent protection than stretched isometric contractions in the lower limb.

Purpose Controversy remains about whether exercise-induced muscle damage (EIMD) and the subsequent repeated bout effect (RBE) are caused by the stretching of an activated muscle, or the production of high force at long, but constant, mus- cle lengths. The aim of this study was to determine the influence of muscle fascicle stretch elicited during different muscle contraction types on the magnitude of EIMD and the RBE. Methods Fourteen participants performed an initial bout of lower limb exercise of the triceps surae. One leg performed sus- tained static contractions at a constant long muscle length (ISO), whereas the contralateral leg performed a bout of eccentric heel drop exercise (ECC). Time under tension was matched between the ECC and ISO conditions. Seven days later, both legs performed ECC. Plantar flexor twitch torque, medial gastrocnemius (MG) fascicle length and muscle soreness were assessed before, 2 h and 2 days after each exercise bout. MG fascicle length and triceps surae surface electromyography were examined across the bouts of exercise. Results We found that both ECC and ISO conditions elicited EIMD and a RBE. ISO caused less damage 2 h after the initial bout (14% less drop in twitch torque, P = 0.03) and less protection from soreness 2 days after the repeated bout (56% higher soreness, P = 0.01). No differences were found when comparing neuromechanical properties across exercise bouts. Conclusion For MG, the action of stretching an active muscle seems to be more important for causing damage than a sus- tained contraction at a long length. Keywords