Knee and Hip Isometric Force Steadiness Are Impaired in Women With Patellofemoral Pain

Ferreira, AS, de Oliveira Silva, D, Ferrari, D, Magalhaes, FH, Pappas, E, Briani, RV, Pazzinatto, MF, and de Azevedo, FM. Knee and hip isometric force steadiness are impaired in women with patellofemoral pain. J Strength Cond Res 35(10): 2878-2885, 2021-The purposes were as follows: to compare knee extension and hip abduction force steadiness and maximal strength between women with patellofemoral pain (PFP) and pain-free women; and to investigate whether maximal strength, self-reported pain during force-matching tasks, self-reported knee function, symptoms duration, and physical activity level are associated with knee extension and hip abduction force steadiness. Thirty women with PFP and 30 pain-free women were recruited. Knee extension and hip abduction maximal voluntary isometric contractions and submaximal isometric force-matching tasks were evaluated using an isokinetic dynamometer. Subjects were asked to match a target force corresponding to 10% of their maximal isometric voluntary contraction while force steadiness was computed as the coefficient of variation (CV) of the exerted force. Women with PFP had significant 36% lower knee extension and 33% lower hip abduction peak strength. They also had significant 70% lower knee extension force steadiness and 60% lower hip abduction force steadiness (i.e., higher CV) than pain-free women. Self-reported pain and self-reported knee function were significantly associated (r = 0.61, p < 0.001; r = -0.35, p = 0.05) and able to predict 41% of the variance of knee extensor force steadiness. Hip abductor maximum strength was significantly associated (r = -0.57; p = 0.001) and able to predict 32% of the variance of hip abductor force steadiness. These findings indicate that muscle impairments in PFP go beyond only low knee and hip muscle strength because women with PFP also present deficits in knee extension and hip abduction force steadiness. Evidence-based treatments aiming at improving force steadiness may be a promising addition to PFP rehabilitation programs.