Objective
Inappropriate neural control of the quadriceps femoris muscle group has been implicated in patellofemoral pain syndrome (PFPS) and the methods of biomechanical assessment of PFPS has been developed recently. The aims of the present investigation were to evaluate the effects of therapeutic exercise in the alleviation of PFPS and to develope objective clinical test for PFPS.

Method
We investigated the onset time of the isometric contraction of vastus medialis oblique muscle (VMO) and the vastus lateralis muscle (VL) under four different conditions: knee flexion and extension in weight bearing (standing) and non-weight bearing (sitting on chair) situations. For each condition, onset times of EMG activities and onset times for VMO and VL were determined from five trials of isometric contraction. In addition, we compared knee flexor and extensor torques in control group and subjects with PFPS. To evaluate the effects of the exercise we compared the onset time difference (onset time of VL-onset time of VM) and quadriceps muscle torque at pre- and post- exercise in PFPS groups.

Results
In PFPS group, onset time of VMO during knee extension was significantly longer than the onset time of VL and the knee extensor torque was considerably weaker in comparison with normal group. Although onset time difference was not changed after exercise program, there were significant increase in knee extensor torque in subjects with PFPS.

Conclusion
The role of exercise in the rehabilitation of quadriceps functions is to reduce the pain, to strengthen the knee extensor, and further accurate diagnostic tools and methods for the result of therapeutic exercise in PFPS are needed.