The first purpose was to compare the difference between leg press exercise(LPE) and additional hip abductor and external rotator muscle strength training to leg press exercise(LPE+HAE) in muscle strength, hip kinematics during step down, pain severity and function for patients diagnosed with patellofemoral pain syndrome. The second one was to discover the relationship between the change in muscle strength performance and the difference of hip joint kinematics post treatment.

Inclusion Criteria:

• Patellofemoral pain syndrome ( Bilateral or unilateral)
• Special tests: crepitus during compression test, patellar grind test (Clarke's sign), pain during compression test, palpation ( at least 2 )
• Below 50 years old
• Pain :after long sitting, up/down stair, squat, kneeling, running & jumping ( at least 2 )
• Pain duration at least 1 month
• At least 1 item of PSS score more than 3 cm

Exclusion Criteria:

• Knee operation
• Central or peripheral neurological deficits
• Obvious knee joint or lower extremity malalignment
• People involved in competitive sports
• PSS sub-scale pain experienced last week more than 8cm
• Have been taking anti-inflammatory drugs , received anti-inflammatory injection or received other therapy for past 3 months