# Patellofemoral Joint Stress During Front and Back Squats at Two Depths
## 3 Results  
Mean and standard deviation (SD) of variables (peak PFJS (MPa), PFJRF (BW), quadriceps force (BW), trunk and knee flexion range of motion (\({}^{\circ}\)), and horizontal bar position to knee and heel) and effect size comparisons between two depths are presented in Table 1.  
The multivariate analysis of variance (MANOVA) did not show any differences between techniques (FS/BS) (F-value = 2.46, \(p\) = 0.083) and revealed no interaction effects  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Back Squat**} & \multicolumn{3}{c}{**Front Squat**} \\ \cline{2-7}  & **60\%** & **80\%** & **60–80\%** & **60\%** & **80\%** & **60–80\%** \\  & **Leg Length** & **Leg Length** & **Effect Size** & **Leg Length** & **Leg Length** & **Effect Size** \\ \hline
**Variables (unit)** & \multicolumn{3}{c}{**Feak (mean \(\pm\) SD)**} & \multicolumn{3}{c}{**Feak (mean \(\pm\) SD)**} \\ \hline Patellofemoral Joint Stress (MPa) & 21.56 \(\pm\) 7.04 & 14.00 \(\pm\) 3.97 & 1.37 & 24.31 \(\pm\) 10.04 & 14.31 \(\pm\) 3.96 & 1.43 \\ \hline Patellofemoral Joint Reaction Force (BW) & 5.80 \(\pm\) 0.72 & 3.78 \(\pm\) 0.65 & 2.95 & 6.23 \(\pm\) 1.14 & 3.79 \(\pm\) 0.80 & 2.52 \\ \hline Quadriceps Force (BW) & 5.97 \(\pm\) 0.75 & 3.86 \(\pm\) 0.65 & 3.01 & 6.28 \(\pm\) 0.81 & 3.87 \(\pm\) 0.79 & 3.01 \\ \hline Knee Flexion angle (\({}^{\circ}\)) & 100.97 \(\pm\) 7.54 & 74.47 \(\pm\) 6.13 & 3.88 & 104.94 \(\pm\) 6.44 & 75.22 \(\pm\) 7.57 & 4.24 \\ \hline Trunk Flexion angle (\({}^{\circ}\)) & 13.46 \(\pm\) 12.11 & 2.83 \(\pm\) 8.76 & 1.02 & 7.34 \(\pm\) 13.65 & \(-\)5.06 \(\pm\) 9.44 & 1.07 \\ \hline Horizontal Bar Position to Knee (m) & 0.16 \(\pm\) 0.04 & 0.11 \(\pm\) 0.03 & 1.43 & 0.25 \(\pm\) 0.04 & 0.21 \(\pm\) 0.03 & 1.14 \\ \hline Horizontal Bar Position to heel (m) & 0.03 \(\pm\) 0.04 & 0.01 \(\pm\) 0.03 & 2.86 & 0.13 \(\pm\) 0.03 & 0.11 \(\pm\) 0.02 & 0.8 \\ \hline \hline \end{tabular}  
* Units: SD: standard deviation, MPa: megapascal, BW: body weight, \({}^{\circ}\) = degrees, m: meter.  
\end{table}
Table 1: Patellofemoral joint stress, patellofemoral joint reaction force, quadriceps force, knee flexion angle, trunk flexion angle, horizontal bar position relative to the knee, and horizontal bar position relative to the heel and effect size (Cohen’s d) comparison between 60% and 80% of leg length depths.  
Figure 4: Patellofemoral Joint Model. Patellofemoral joint reaction force (PFJRF), quadriceps force (QF), patellofemoral joint contact area, and patellofemoral joint stress (PFJS).  
(F-value = 0.97, \(p\)= 0.45). However, the MANOVA showed a difference between the two squat depths (F-value = 70.18, \(p\)\(<\) 0.001). Follow-up univariate analysis indicated a greater PFJS, PFJF, quadriceps force, trunk ROM, knee ROM, horizontal bar position to knee and heel during the 60% squad depth (\(p\)\(<\) 0.001).  
The 60% leg length depth condition had 62% greater PFJS (\(p\)\(<\) 0.001), 59% greater PFJF (\(p\)\(<\) 0.001), 58% greater quadriceps force (\(p\)\(<\) 0.001), and 38% greater knee flexion range of motion (\(p\)\(<\) 0.001). Higher depth causes a higher trunk ROM or trunk flexion by 89% (\(p\)\(<\) 0.001), a higher knee flexion by 27% (\(p\)\(<\) 0.001), a greater relative horizontal bar position to the knee (29% (\(p\)\(<\) 0.001)) and to the heel (25% (\(p\)\(<\) 0.001)) for both squat techniques.  
Figure 5 shows ensemble averaged PFJS (A), quadriceps force (B), and knee flexion angle (C) during all four conditions. It seems that PFJS is at the highest during the middle part of squatting when the knee flexion angle and quadriceps force are at the highest.