BACKGROUND AND AIMS: This study was performed to compare the effects of open and closed chain terminal knee extension exercises on onset latency of vastus medialis obliques (VMO) and vastus lateralis (VL), pain and function in subjects diagnosed with patellofemoral pain syndrome (PFPS). METHODS: In a pretest and posttest 5-week intervention study, 26 subjects diagnosed with PFPS and 13 healthy subjects were studied. Subjects diagnosed with PFPS were divided into two groups. One group (n = 13) participated in a 5-week rehabilitation program consisted of open chain terminal knee extension exercise and the other group's program (n = 13) consisted closed chain terminal knee extension exercise. Electromyographic onsets of VMO and VL collected during step up and step down tasks performed during the pretest and posttest. A visual analog scale (VAS) and Lysholm questionnaire were administered at pretest and posttest. Analysis of variance was used to compare the three groups. T-test and paired t-test were also used for statistical analysis. RESULTS: VMO and VL onsets timing in PFPS groups were significantly more than those in the control group at the base line (p < 0.05). VMO and VL onset timing differences (VL electromyographic onset minus VMO electromyographic onset) significantly decreased and VAS and Lysholm scores significantly improved for subjects diagnosed with PFPS after intervention (p < 0.05). There was no significant difference between the outcomes of two intervention programs in patients with PFPS. CONCLUSION: Subjects diagnosed with PFPS responded favorably and quickly to therapeutic exercises program that incorporated open and closed chain exercises.

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