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.