The effect of squat load and depth on patellofemoral joint kinetics

The squat exercise is prescribed in a wide variety of situations ranging from performance enhancement to rehabilitation. Although widely used, there is dispute among professionals as to what depth should be prescribed. With patellofemoral pain being one of the most common disorders of the knee, it is important to better understand the patellofemoral forces at differing loads and depths of the squat exercise. In general, decreasing loads are needed when depth of the squat is increased. It was hypothesized that the decreased loads often seen with increasing depths would result in no difference in patellofemoral joint reaction forces (PFJRF). A secondary purpose of this study was to find a relationship between squat one repetition max (1RM) and depth to help predict squat loads at deep depths from one repetition max achieved at a higher depth.;Sixteen males with no previous leg surgeries and at least one year of experience resistance training participated in the study. Subjects were visually screened before participation to ensure adequate depth could be achieved. One repetition max testing was conducted at three different depths of above parallel (∼ 90°), parallel (∼110°), and below parallel (∼135°). Subsequently, motion capture testing at the same depths under unloaded, 50% 1RM, and 85% 1RM conditions was performed. A total of 9 trials were completed utilizing the three depths and loads. An addition 4 trials were completed at the parallel and above parallel depths using the below parallel 50% and 85% 1RM loads to assess the effect of depth on PFJRF with constant loads.;Post-test analysis revealed that peak knee moments and PFJRF were significantly different at all depths with a %1RM and constant load (p < 0.05). Peak knee moments and PFJRF were also significantly different with increasing loads for each squat depth (p < 0.05). Unloaded parallel and below parallel squats were not significantly different. One repetition max loads were significantly different at all levels (p < 0.05). A regression equation was developed to predict both parallel (R2 = 0.764) and below parallel (R 2 = 0.641) from a 90° above parallel squat.;The main finding of this study was that typical decreases in weights used with increasing depths are not enough to offset the increases in PFJRF typically seen with increasing knee flexion. Interpretation of these results should be done with caution as there are many other variables involved in the squat exercise. These results, along with a proper individualized assessment, may better help in the utilization of the squat exercise in rehabilitation and training programs.