Hip rate of force development and strength are impaired in females with patellofemoral pain without signs of altered gluteus medius and maximus morphology

Objectives: To compare rate of force development (RFD) and isometric muscle strength of the hip abductors and extensors; and the thickness and the amount of non-contractile tissue of the gluteus medius and maximus between females with and without patellofemoral pain (PFP). Design: Cross-sectional study. Methods: Fifty-four physically active females (27 with PFP and 27 healthy individuals) were studied. Hip muscle isometric strength and RFD was evaluated using isokinetic dynamometry. RFD was measured until 30%, 60%, and 90% of the maximal isometric torque (MIT). Hip muscle morphology was evaluated using ultrasonography. Results: The PFP group possessed slower RFD compared to the control group by 33% for hip abductors until 90%MIT (-0.23%/ms, 95%Cl -0.44 to -0.02, ES = 0.59); by 51% for hip extensors until 30%MIT (-0.42%/ms, 95%Cl -0.66 to -0.18, ES = 0.97): and by 55% for hip extensors until 60%MIT (-0.36%/ms, 95%Cl -0.60 to -0.12, ES = 0.81). The PFP group possessed reduced isometric torque compared to the control group by 10% for hip abduction (-16.0 Nm/kg x 100, 95% CI -30.2 to -1.9, ES = 0.61) and by 15% for hip extension (-30.1 Nm/kg x 100, 95%Cl -51.4 to -8.9, ES = 0.76). No significant between group differences for the thickness and the amount of non-contractile tissue of the gluteus medius and maximus were identified. Conclusions: Females with PFP have deficits in isometric strength and RFD in hip abduction and extension. RFD deficits are greater than strength deficits which may highlight their potential importance. Hip muscle strength and RFD deficits do not appear to be explained by muscle thickness or proportion of non contractile tissue of the gluteal musculature as measured by ultrasound. (C) 2017 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved. (AU)