Patellofemoral joint forces and stress during forward step-up, lateral step-up, and forward step-down exercises

Abstract

STUDY DESIGN: Controlled laboratory study using a repeated-measures design. OBJECTIVE: To quantify patellofemoral joint reaction force (PFJRF) and stress (PFJS) during forward step-up (FSU), lateral step-up (LSU), and forward step-down (FSD) exercises. BACKGROUND: Although FSU, LSU, and FSD exercises are commonly used in patellofemoral joint rehabilitation programs, the influence of these stepping tasks on patellofemoral joint kinetics has not been quantified. METHODS: Three-dimensional lower extremity kinematics and kinetics and electromyographic (EMG) data were obtained from 20 healthy adults during their performance of FSU, LSU, and FSD exercises. The step height for each participant was adjusted to permit a standardized knee flexion angle of 45°. A previously described biomechani¬cal model of the patellofemoral joint was used to quantify PFJRF and PFJS during each task. Peak PFJRF and PFJS during the concentric and eccen¬tric phases of each step task were compared using a 2-factor analysis of variance (ANOVA). RESULTS: When collapsed across concentric and eccentric phases, peak PFJS was significantly greater during the FSD (mean ± SD, 13.8 ± 0.4 MPa) compared to the LSU (11.5 ± 0.8 MPa; P < .001) and FSU (11.2 ± 0.6 MPa; P = .002) ex-ercises. Peak PFJRF also was significantly greater during the FSD (51.1 ± 2.7 N/kg) compared to the LSU (44.1 ± 3.4 N/kg; P < .001) and FSU (43.6 ± 2.3 N/kg; P = .023) exercises. CONCLUSION: In selecting exercises that promote lower extremity muscle strengthening while minimizing patellofemoral joint loading, LSU and FSU should be considered over FSD exercises, if the same step height is used.