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Barbosa, GM, Trajano, GS, Dantas, GAF, Silva, BR, and Vieira, WHB. Chronic effects of static and dynamic stretching on hamstrings eccentric strength and functional performance: A randomized controlled trial. J Strength Cond Res XX(X): 000–000, 2019—The purpose of this study was to investigate the effect of static or dynamic stretching training program on hamstrings eccentric peak torque and functional performance. Forty-five active healthy men were randomly allocated into 3 groups (n = 15 per group): no stretching (control), static stretching (3 sets of 30 seconds), and dynamic stretching (3 sets of 30 repetitions). Static and dynamic stretching protocols on the hamstring muscles were performed 3 times a week until complete 10 sessions. Isokinetic knee flexor eccentric peak torque (60°·s−1), triple hop distance, and modified 20-m sprint time were assessed in a random order before and after stretching training. A mixed-design analysis of variance was performed, with an alpha level of 0.05. There was a significant decrease of eccentric peak torque (p ≤ 0.0001, −15.4 ± 10.4%, within-group effect size: 1.03) after static stretching training. The static stretching training reduced eccentric torque when compared with no stretching (−7.6 ± 21.7%, between-group effect size: 0.50) and dynamic stretching (−7.8 ± 29.8%, between-group effect size: 0.51). Moreover, the reached distance on triple hop test was also reduced after static stretching protocol (p = 0.009, −3.7 ± 4.1%, within-group effect size: 0.29). These findings suggest that static stretching training is sufficient to produce meaningful reductions on hamstrings eccentric torque and functional performance. Based on the results of this study, caution should be taken when prescribing of static stretching training in isolation when the purpose is to improve performance, and indirectly, to prevent hamstring strain injuries due to its possible negative effects on hopping performance and knee flexor eccentric torque.