Background & purpose One of the common injuries in soccer is hamstring strain, so improving hamstring flexibility can partially prevent the occurrence of these injuries. The aim of the present study was to compare the effects of six weeks of static stretching (SS), proprioceptive neuromuscular facilitation (PNF), muscle energy technique (MET), gross tonic technique (GT), and foam rolling (FR) on hamstring flexibility in adolescent male soccer players. Methods Ninety male soccer players (mean aged = 13.01 ± 1.11 years) were randomly assigned to five intervention groups and a control group (n = 15 each), underwent a 6-week intervention, with flexibility assessed pre- and post-intervention using a universal goniometer and the active knee extension test. Results One-way ANCOVA, controlling for pretest values, showed a significant difference between groups (F(5, 83) = 22.79, p < 0.001, n² = 0.57). All intervention groups showed significant improvement compared to control (p < 0.001). The GT group was superior to MET (p = 0.01; Cohen`s d = - 1.23), PNF (p = 0.004; Cohen`s d = - 1.40), and FR (p = 0.02; Cohen`s d = - 1.19), but no difference was observed with SS (p > 0.05; Cohen`s d = - 0.75). Conclusion All methods improved hamstring flexibility, but GT was the most effective (except when compared with SS). These findings suggest the potential use of GT in training programs to reduce injury and improve performance in adolescent soccer players. However, since the study included only adolescent male players and no long-term follow-up was performed, generalizability is limited. Trial registration Registry: Iranian Registry of Clinical Trials; registration number: IRCT20240306061185N2; date of registration: 08/03/2024.
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