Fig. Patellofemoral joint stress profiles of the 3 exercises evaluated in the current study. *Significant difference from EXT-VR. †Significant difference from EXT-CR. Abbreviations: EXT-CR, knee extension with constant resistance; EXT-VR, knee extension with variable resistance. 3 exercises 👇 "Ten healthy subjects participated in a study in which their 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. Compared 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. To minimize PFJ stress while performing quadriceps exercises, the above 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 [The subjects are all normal healthy, so for those with PF pain syndrome or knee arthritis, once need to apply this finding wisely with scientific reasoning] https://www.facebook.com/share/p/1F4KDhCd6E/