Objective: Studies that investigated possible correlations between flexibility and muscular performance are scarce in the literature. Therefore, the purpose of this study was to investigate the impact of a program of static stretching on the flexibility of the hamstrings and on muscular performance of the knee flexors and extensors. Design: Pre-post experimental design. Setting: University laboratory. Participants: Thirty subjects aged 22.8 +/- 4.9 years with bilaterally shortened hamstrings. Intervention: Using a protocol that has been previously described, the intervention consisted of 30 sessions of static stretching, performed bilaterally five times a week for 6 weeks. Main Outcome Measurements: Measures of knee range of motion and isokinetic muscular performance (peak torque, angle of peak torque, and work) of knee flexors and extensors at speeds of 60 and 300 degrees/s. Results: After intervention, significant gains in measures of flexibility (P < 0.0001) were observed, with an average gain of the knee-extension angle of 12.6[degrees], ranging from -1.2 to 30.7[degrees]. In addition, we found significant increases in the following parameters of muscular performance: angle of peak torque of hamstrings at 60 and 300 degrees/s (P < 0.0001 and 0.018) and for work at 60 and 300 degrees/s for knee flexors (P = 0.012 and 0.005) and for knee extensors (P < 0.0001). Conclusions: The intervention resulted in gains in measures of flexibility, and these gains had a positive impact on some parameters of muscular performance.
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