Background: Patellofemoral pain syndrome (PFPS) is a common disorder of the knee joint complex which affects both active and sedentary women
The cause of this disorder is multifactorial and its etiology has not yet been completely explained. Biomechanical factors and muscle function are often analyzed in attempts to identify the etiology
of PFPS and establish effective treatment plans that will lead to clinical improvements in patients. To compare the concentric and eccentric activity and the temporal order of peak activity of the hip
and knee muscles of women with patellofemoral pain syndrome during the single leg triple hop test (SLTHT).
Methods: Fourteen healthy women (CG) and 14 women with PFPS (PFG) were included in this investigation. Integral EMG (iEMG) data was calculated for the eccentric and concentric phases
of the second jump in the SLTHT, with a focus on the following muscles: gluteus maximus, gluteus medius, biceps femoris and the vastus lateralis. The length of time that each muscle needed to reach
the maximal peak of muscle activity from the first contact of the foot with the ground (during the landing) was also calculated.
Results: A significant increase in the iEMG (p < 0.05) was recorded in the eccentric phase, when compared with the concentric phase, for the gluteus maximus and gluteus medius muscles
(CG and PFG) and for the vastus lateralis muscle (PFG). The vastus lateralis muscle was the first muscle to reach the highest peak of activity in the PFG, and the third to reach this peak in the CG.
Conclusions: In the present study, there was a significant increase in the activity of the vastus lateralis muscle during the eccentric phase of the jump, when compared with the
concentric phase. There was also a temporal anticipation of its peak in activity among women with PFPS.