Quadriceps strength loss at flexed knee angles in active high-level soccer players with patellofemoral pain

Abstract

. Patellofemoral pain (PFP) appears in actions that increase patellofemoral compressive forces such as forceful quadriceps contraction in a flexed knee position. PFP has been associated with quadriceps strength decrease and disturbances ('breaks') in the torque-angular position. Twenty two active high-level soccer players with PFP and breaks in the quadriceps isokinetic curve were studied. The results showed that the quadriceps strength was significantly reduced in comparison with the uninvolved side, being more affected at flexed angles of the knee. A single break in the quadriceps torque-angular position curve started on average at 73 ± 7° reaching the maximum break at 65 ± 7° and recovering at 54 ± 9°. At the minimal within-break torque angle the average reduction was 30.6% while the PT was reduced by 18.4%. Sub-clinical PFP in high-level soccer players may be related to a significant loss in quadriceps muscular performance in the first part of knee extension possibly affecting common soccer tasks such as kicking, jumping or tackling. Isokinetic concentric testing may be used to detect and characterize this alteration.