A common component of rehabilitation for patients with patellofemoral paint (PFP) includes strengthening of the quadriceps, performed both in an open- and closed-kinetic chain manner (non-weight-bearing and weight-bearing respectively). Clinicians must consider exercise prescription with respect to minimising patellofemoral joint (PFJ) loading. The aim of the following study was to compare patellofemoral joint (PFJ) stress between the two.

Lower extremity kinematics, kinetics, and electromyography of the quadriceps were recorded in 10-healthy individuals performing a weight-bearing squat, which was compared to non-weight-bearing knee extension.

The squat yielded significantly greater PFJ stress at 90°, 75°, and 60° of knee flexion. In contrast, the non-weight-bearing knee extension produced significantly higher PFJ stress at 30°, 15°, and 0° of knee flexion.

These findings provide general guidelines with respect to quadriceps strengthening amongst people with PFP. To minimise PFJ stress, it is suggested that weight-bearing squats should be performed between 45° and 0° of knee flexion; whilst non-weight-bearing extension is optimally performed in the range of 90° to 45°. > From: Powers et al., J Orthop Sports Phys Ther (2014) (Epub ahead of print). All rights reserved to Journal of Orthopaedic & Sports Physical Therapy.

Study DesignSingle-group, repeated-measures design.

ObjectiveTo compare patellofemoral joint (PFJ) stress among weight-bearing and non-weight-bearing quadriceps exercises.

BackgroundAn important consideration when 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.

MethodsTen 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.

ResultsCompared to the 2 non-weight-bearing 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-with-variable-resistance exercise produced significantly lower PFJ stress than the knee-extension-with-constant-resistance exercise at 90°, 75°, and 60° of knee flexion.

ConclusionTo minimize PFJ stress while performing quadriceps exercises, our data suggest that the squat exercise should be performed from 45° to 0° of knee flexion and the knee-extension-with-variable-resistance exercise should be performed from 90° to 45° of knee flexion. J Orthop Sports Phys Ther 2014;44(5):320–327. Epub 27 March 2014. doi:10.2519/jospt.2014.4936

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