The purpose of this study is to determined if a lower back treatment would change the hip and knee muscle activities in people with and without anterior knee pain. The investigators hypothesized that the lower back treatment may change the hip and knee muscle activities in people with anterior knee pain but not in people without anterior knee pain.

Inclusion Criteria for participants in the patellofemoral pain syndrome group:

1. insidious onset of symptoms of non-traumatic origin

2. pain with patellar facet palpation or compression

3. subjective knee pain rating of at least 3/10 on the pain visual analog scale during at least one of the following activities:

   • ascending stair
   • descending stair
   • kneeling
   • squatting
   • running
   • jumping
   • prolong sitting for more than 20 minutes

Exclusion criteria for all participants:

1. history of spine, hip or knee surgery
2. history of hip pathology or other knee condition
3. current significant injury of any lower extremity joints
4. pregnancy
5. sign of nerve root compression
6. osteoporosis or history of compression fracture

Age- and gender- matched control participants will be recruited if they have no signs or symptoms of patellofemoral pain syndrome and have none of the exclusion criteria