Background and aim: Muscle flexibility is an important component of physical fitness and injury prevention.

Passive Stretch can be effective in lengthening and making hamstring more flexible. Popliteal angle measurement is one of the most simple method in studying the efficiency of these methods however, in goniometry measurement, there is not any data about muscle tension and any proper judgment about flexibility.  The goal of this study is to evaluate length and stiffness of the hamstrings by Quick Release Movement before and after the passive stretch.

Materials and methods:14 men (20-30 years old) with shorted hamstring (20 degree or more ext lack in passive knee ext test by popliteal angle measurement) participated in this study. Before and after exercises, popliteal angle  and muscle stiffness  were evaluated with digital goniometer and  Quick Release Movement technique respectively. Evaluation of stiffness was performed in flexion and extension positions.

Results: A significant increase in hamstring length was observed. (P<0.05) There was decrease in stiffness in both position of flex and ext but it was significant when in extension state.(P<0.05)

Conclusion: Findings of this study demonstrate passive stretch's effectiveness in increase muscle length and lessening muscle stiffness. In addition Quick Release Movement can be a suitable method for measuring muscle stiffness.