Objectives: This study aimed to examine the effects of unilateral long-duration static stretching (LS) on range of motion (ROM), musculotendinous unit (MTU) stiffness, muscle thickness (MT), strength, and contralateral effects (CE) in young men with hamstring tightness. Methods: Sixty-eight young men (22.0±1.7 years) were randomly assigned to one of four groups: LS, typical-duration static stretching (SS), hamstring resistance exercise (HRE), or control. ROM, MTU stiffness, MT, and knee-flexor peak torque were assessed at baseline, after the 6-week intervention, and at the 3-month follow-up. Results: ROM improvement after the 6-week was observed across the LS, SS, and HRE groups (all p<0.05). Significant decreases in MTU stiffness were observed, with reductions of 0.13 Nm/deg in the hamstrings for both the stretching groups (all p<0.05). At the 3-month follow-up, reductions in MTU stiffness remained evident in the LS group. A significant time effect was observed for bilateral peak torque without interaction or group effects, while MT showed no changes. Conclusions: One hour of hamstring stretching did not result in superior improvements in ROM, MTU stiffness, or morphological and CE adaptations compared to other exercise modalities. Nevertheless, SS remains a time-efficient approach to enhance flexibility and mechanical properties in a home-based setting. Clinical trial registration: Thai Clinical Trials Registry (TCTR20250219007).