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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.

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Background and Aim: This study was performed to compare the stiffness of hamstring and rectus femoris muscles in subjects with anterior knee pain and normal subjects.

Materials and Methods: In this non experimental and case-control study, 20 persons with anterior knee pain were selected simply from convenient sample and 20 healthy persons were selected by matching method. proximal and distal stiffness of hamstring and rectus femoris muscles were measured using an isokinetic device in the passive mode. Also, maximal concentric peak torque during flexion and extension movements of hip and knee, in two groups were compared by independent T-test and correlation analysis.

Results: There was no significant difference between anterior knee pain and proximal compartment of rectus femoris(P=0.320) and hamstring(P=0.125) stiffness, but there was significant difference between anterior knee pain and distal compartment of rectus femoris and hamstring stiffness (P<0.001). Significant relationship was found between anterior knee pain and muscles strength (P<0.001). No correlation was found between strength and stiffness of rectus femoris (P=0.356) and hamstring muscles (P=0.643) in patients group, but in healthy subjects this relationship was found (P<0.001). 

Conclusion: In patients with anterior knee pain, hamstring and rectus femoris muscles stiffness increased and muscle strength decreased. Increasing of muscle strength was effective on stiffness in healthy subjects, but there was no relation between them in patients group. Also rectus femoris and hamstring muscles possibly have different proximal and distal neuromuscular compartments.