Quadriceps strengthening is a common com ponent of the rehabilitation program for persons with patellofemoral pain (PFP) and typically includes weightbearing and non-weight bearing exercises. 1,9,12,18,27 Both forms of exercise have their advantages with respect to quadriceps strengthening. Weight bearing exercises are more functional in nature 7,11 and incorporate contractions of multiple agonist and antagonist muscle groups.
1921,25In contrast, nonweight-bearing knee extension exercises require less cocontraction of antagonist muscles thus provide better quadriceps muscle isolation.
5When designing a quadricepsstrengthening program for individuals with PFP, it is important to select exercises that promote muscle loading and adaptation and minimize patellofemoral joint (PFJ) stress and pain. Steinkamp and colleagues 17 first described the influence of weight-bearing status on PFJ stress. These authors reported a contrast in the pattern of PFJ stress during weight-bearing and non-weight-bearing exercises performed at 0° to 90° of knee flexion. During the weight-bearing task (leg press), PFJ stress increased linearly from 0° to 90° of knee flexion.17 During the non-weight-bearing knee extension exercise, however, PFJ stress was greatest at 0° and decreased with knee flexion.
17The findings of Steinkamp et al 17 have been challenged by Escamilla and colleagues, 6 who quantified PFJ reaction forces during similar weight-bearing and non-weight-bearing tasks (squat and knee extension, respectively). These authors reported that the PFJ reaction T T STUDY DESIGN: Single-group, repeatedmeasures design.
T T OBJECTIVE:To compare patellofemoral joint (PFJ) stress among weight-bearing and nonweight-bearing quadriceps exercises.
T T BACKGROUND: An important considerationwhen prescribing exercises to strengthen the quadriceps in persons with patellofemoral pain is to minimize PFJ loading. Currently, there is disagreement in the literature as to which exercises and ranges of motion best accomplish this goal.
T T METHODS:Ten healthy subjects participated.Lower extremity kinematics, kinetics, and electromyography of the knee musculature were obtained during a weight-bearing squatting exercise and 2 non-weight-bearing knee extension exercises: (1) knee extension with variable resistance, and (2) knee extension with constant resistance. A previously described biomechanical model was used to estimate PFJ stress at 0°, 15°, 30°, 45°, 60°, 75°, and 90° of knee flexion. PFJ stress was compared among the 3 exercises using a 2-way analysis of variance with repeated measures.
T T RESULTS:Compared to the 2 non-weightbearing exercises, the squat exercise produced significantly higher PFJ stress at 90°, 75°, and 60° of knee flexion. Conversely, the 2 non-weight-bearing exercises produced significantly higher PFJ stress at 30°, 15°, and 0° of knee flexion when compared to the squat exercise. The knee-extension-withvariable-resistance exercise produced significantly lower PFJ stress than the knee-extension-withconstant-resistance exercise at ...