# Patellofemoral Joint Stress During Front and Back Squats at Two Depths
## 4 Discussion
It appears that PFJS increases as both resistance (no load to 50%, and 85-90% 1 RM) and squat depth (above parallel, parallel, and below parallel) increase. While we used a fixed load in our study, joint loading variables increased with increasing depth in accordance with prior investigations. A future investigation may test if there is an interaction effect on joint loading between bar location and load. [PERSON] and [PERSON] (2018) reported a significant difference in PFJS while squatting as anterior knee position relative to the foot changed [4]. Based on that investigation, we hypothesized that the knee position would result in a difference in PFJS between a front squat and a back squat. However, these hypotheses were not supported by the results of the present study. It has been previously reported that patellofemoral joint contact area increased with greater knee flexion as assessed by MRI imaging [31]. Patellofemoral joint contact area depends on many different factors including gender, body size, joint size, the external load, and knee flexion angle [20]. In this study, the contact area of healthy subjects during the knee flexion of 15, 30, and 45 degrees was used [23] in the regression model as function of knee angle [23]. In general, as the knee flexes, the quadriceps muscles eccentrically contract, producing a force between the patella and the femoral condyles. This force contributes to the PFJRF, with greater quadriceps muscle force [31] resulting in a greater PFJRF. The contact area between the patella and the femur is not consistent throughout the knee's range of motion, thus the magnitude of PFJRF will vary depending on the angle of knee flexion. As the contact area between the patella and femur increases with greater knee flexion (greater squat depth), more compressive force is applied through the joint and PFJS will increase. This may explain why our study found increased PFJS with greater squat depth. This study is not without limitations. The first is that the external applied load may have been insufficient to create a significant difference in patellofemoral joint loads and stress between the front and back squat. Our study did not include a bodyweight-only condition that could be used as a reference. Within this study's sample, the load was consistent for all the participants, potentially creating variability in exertional intensities across participants. However, we utilized a repeated measures design, therefore, the comparisons were likely relevant across the different squat types. A final limitation is the effect of potential fatigue on the participants' performance. For instance, due to incorrect adherence to the protocol, some participants had to perform multiple trials to meet study's criteria, so results of the later trials performed by these individuals may have been influenced by muscle fatigue. Further research may be warranted to normalize the amount of applied load relative to the participants 1 RM, or to allow for more skilled practice to minimize trial repetitions due to inconsistency. Future studies could also incorporate electromyography (EMG) to gain a deeper understanding of muscle activation patterns.