The Effect of Real-Time Feedback Regarding the Center-of-Pressure Position on Patellofemoral Joint Loading During Double-leg Squatting

Background: Exercise therapy is the cornerstone of patellofemoral (PF) pain management. However, whether squat exercises are therapeutic or detrimental depends on their technique and the resulting load on the PF joint. Purpose/Hypothesis: The purpose of this study was to investigate whether real-time feedback to position the center-of-pressure (COP) anteriorly could reduce the PF joint reaction force and stress during bodyweight double-leg squatting. It was hypothesized that an anterior COP position would decrease the PF joint reaction force and stress without changing the trunk flexion angle, whereas a posterior COP position would increase the PF joint reaction force and stress. Study Design: Controlled laboratory study. Methods: Sixteen men (age, 22.9 +/- 1.5 years; height, 173.6 +/- 5.2 cm; and body mass, 63 +/- 6.8 kg) performed double-leg squatting under 4 conditions-natural, anterior, middle, and posterior COP. Kinematic and kinetic data were obtained via standard 3-dimensional motion analysis and force plate data. The PF joint reaction force and stress were calculated via a musculoskeletal modeling approach. Results: PF joint loading was significantly reduced in the anterior and middle COP conditions compared with the natural condition. At 90 degrees of knee flexion, the PF joint reaction force decreased by 11% and 9% in the anterior and middle COP conditions, respectively, compared with that in the natural condition (anterior: P < .001, 95% CI -0.996 to -0.277 bodyweight; middle: P = .011, 95% CI -0.795 to -0.087 bodyweight). Moreover, the peak PF joint stress decreased by 9% and 7% in the anterior and middle COP conditions, respectively, compared with the natural condition (anterior: P = .001, 95% CI -0.659 to -0.146 MPa; middle: P = .023, 95% CI -0.600 to -0.036 MPa). Compared with those under the natural condition, the trunk forward inclination angles did not increase under anterior or middle COP conditions. Conclusions: Real-time feedback for anterior COP positioning is an effective strategy for reducing the PF joint reaction force and stress during double-leg squatting without increasing trunk forward lean.