Abstract
Background: Temporal difference in activation of medial-lateral hamstrings could lead to external tibial rotation. It was assumed that patients with patellofemoral pain syndrome (PFPS) exhibit altered medial-lateral hamstrings muscular pattern during functional tasks.
Objectives: The aim of this study was to compare the electromyography (EMG) activity of quadriceps and hamstrings in patients with PFPS and healthy subjects during stair descending.
Design: cross sectional comparative study
Setting: Motion analysis Lab, Rehabilitation research center, Shiraz University of Medical Sciences
Participants: 24 women with PFPS and 24 healthy subjects, aged 18-40 years recruited through convenience sampling method participated in this study.
Interventions: The EMG activity of vastus medialis obliqus (VMO), vastus lateralis (VL), medial (MH) and lateral hamstrings (LH) recorded during stair descending.
Main outcome measures: Onset latency and intensity of muscle activity measured relative to the moment of foot contact.
Results: There were statistically significant difference in onset of hamstrings heads (LH-MH) between groups (p=0.014). The BF activated before ST in PFPS group. Normalized muscular activity was significantly reduced for VMO (p=0.002), VL (p=.045), and LH (p=0.019) in PFPS patients.
Conclusions: Difference in temporal activation patterns of BF and ST may result in lack of rotational knee stabilization and lead to increased patellofemoral joint pressure. Earlier activation of LH rotates tibia externally, and hence, produced lateral patellar tracking.