Patellofemoral Joint Loading during the Performance of the Wall Squat and Ball Squat with Heel-to-Wall-Distance Variations

Abstract

ABSTRACT Introduction Although bodyweight wall and ball squats are commonly used during patellofemoral rehabilitation, patellofemoral loading while performing these exercises is unknown, which makes it difficult for clinicians to know how to use these exercises in progressing a patient with patellofemoral pathology. Therefore, the purpose was to quantify patellofemoral force and stress between two bodyweight squat variations (ball squat vs wall squat) and between two heel-to-wall-distance (HTWD) variations (long HTWD vs short HTWD). Methods Sixteen participants performed a dynamic ball squat and wall squat with long HTWD and short HTWD. Ground reaction force and kinematic data were used to measure resultant knee force and torque from inverse dynamics, whereas electromyographic data were used in a knee muscle model to predict resultant knee force and torque, and subsequently, all these data were inputted into a biomechanical computer optimization model to output patellofemoral joint force and stress at select knee angles. A repeated-measures two- and three-way ANOVA (P < 0.01) was used for statistical analyses. Results Collapsed across long HTWD and short HTWD, patellofemoral joint force and stress were greater in ball squat than wall squat at 30° (P = 0.009), 40° (P = 0.008), 90° (P = 0.003), and 100° (P = 0.005) knee angles during the squat descent, and greater in wall squat than ball squat at 100° (P < 0.001), 90° (P < 0.001), 80° (P = 0.004), and 70° (P = 0.009) knee angles during squat ascent. Collapsed across ball and wall squats, patellofemoral joint force and stress were greater with a short HTWD than a long HTWD at 100° (P = 0.007) and 90° (P = 0.008) knee angles during squat ascent. Conclusions Patellofemoral joint loading changed according to both squat type and HTWD variations. These differences occurred in part due to differences in forces the wall or ball exerted on the trunk, including friction forces. Overall, patellofemoral force and stress were greater performing the bodyweight wall squat compared with the bodyweight ball squat. Moreover, squatting with short HTWD produced anterior knee displacement beyond the toes at higher knee angles, resulting in greater patellofemoral force and stress compared with squatting with long HTWD.