Chen, CH, Ye, X, Wang, YT, Chen, YS, and Tseng, WC. Differential effects of different warm-up protocols on repeated sprints-induced muscle damage. J Strength Cond Res 32(11): 3276-3284, 2018-The purpose of this investigation was to examine whether adding a set of hamstring resistance exercise or dynamic stretching to a regular running-based warm-up before a bout of repeated sprints provides protective effects against the sprinting-induced muscle damage. Twelve elite tennis players participated in this study. After the familiarization, subjects completed 3 separate randomly sequenced experimental visits, during which 3 different warm-up interventions were performed before the muscle-damaging protocol (12 sets of 30-m maximal repeated sprints): 5 minutes of running (control); control with single leg slide curl (SLC); and control with active hamstring stretching (AHS). Before, immediately (POST0), 1 day (POST1), and 2 days after (POST2) the sprints, hip flexion passive range of motion, hamstring muscle thickness and pennation angle, muscle stiffness, and knee flexion concentric peak torque were measured. Repeated sprints have induced muscle damage in all 3 visits. For AHS, the muscle thickness and stiffness values at POST2 were significantly lower than those of other 2 protocols. In addition, the decrements of concentric strength at POST0, POST1, and POST2 for AHS were also significantly less than those of control and SLC. Therefore, adding a set of dynamic hamstrings stretching to a regular warm-up protocol before repeated sprints has protective effect on the sprinting-induced muscle damage. Athletes whose competitions are densely scheduled (e.g., tennis player in a tournament) may take advantage of this strategy to facilitate muscle recovery from the potential muscle damage, thus, to get maximal recovery for the subsequent competitions.