# Estimation of Tibiofemoral and Patellofemoral Joint Forces during Squatting and Kneeling
## 4 Discussion
### Relevance of Thigh-Calf Contact Forces during Squatting and Kneeling  
During kneeling, the relatively low compressive knee joint forces can be primarily attributed to the distribution of the ground reaction forces onto the knee and the foot, \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Author** & **Activity** & **Model Approach** & **Measurement Equipment** & **Knee flexion Angle (Degrees)** & **Knee Joint Moment (N-m/kg)** & **Quadicops Force (BW \({}^{1}\))** & **Tibiofemoral Joint Force (BW)** & **Patellofemoral Joint Force (BW)** \\ \hline [PERSON] et al. [15] & Slow lowering to/slow rising from squat & 2D inverse, EMG & \(\text{MOCAP}\,^{2}\); 1 \(\text{FP}\,^{3}\); EMG \({}^{4}\) & 140 \({}^{8}\) & & \(5.1\pm 0.2\) & \(4.9\pm 0.3\) & \(6.1\pm 1.9\) \\ [PERSON] et al. & Squatting & 3D inverse & \(\text{MOCAP}\,^{2}\); \(\text{PSM}\) \({}^{35}\) & \(155\pm 10\)\({}^{8}\) & \(0.7\pm 0.5\) & & & \\
[24] & Deep kneeling & & \(155\pm 10\)\({}^{8}\) & \(0.5\pm 0.3\) & & & & \\  & Kneeling & & \(110\pm 10\)\({}^{8}\) & \(0.2\pm 0.1\) & & & & \\ [PERSON] et al. [17] & Full squat & 2D inverse, EMG & \(\text{MOCAP}\,^{1}\); \(\text{FP}\) & 155 & 0.7 \({}^{8}\) & \(4.5\pm 1.1\)\({}^{8}\) & \(6.7\pm 1.9\)\({}^{8}\) & \\ [PERSON] et al. [20] & Squatting bebs & \(2\times 2\)D down & \(2\times 2\) inverse & \(\text{MOCAP}\,^{1}\); \(\text{FP}\) & \(135\pm 10\)\({}^{8}\) & & & \(2.0\pm 0.5\)\({}^{8}\) & \\  & Squatting bebs & & & \(145\pm 5\)\({}^{8}\) & & & & \(3.0\pm 0.5\)\({}^{8}\) & \\ [PERSON] [21] & Squatting & 2D inverse & \(\text{MOCAP}\,^{1}\); \(\text{FP}\) & \(142\pm 5\) & \(0.8\pm 0.3\)\({}^{8}\) & & \(2.3\pm 1.0\) & \\ [PERSON] et al. [37] & Squat (normal & 3D inverse) & \(\text{FLIM}\,^{5}\); \(\text{FP}\) & \(150\)\({}^{8}\) & & \(1.8\pm 0.1\) & & \(1.9\pm 0.1\) \\ [PERSON] et al. [23] & Squatting & 2D inverse & \(\text{KINSIM}\,^{7}\) & 155 & & & & 3.1 & \\  & lowering & & \(\text{MOCAP}\) & 145 & & & & 7.0 & \\ [PERSON] et al. [14] & to/rising from squat & & \(\text{KINSIM}\) & & & & & \\  & lowering & & \(\text{MOCAP}\); \(\text{FP}\); & & & & & \\ [PERSON] et al. [16] & to/rising from squat & 3D inverse & EMG, & \(139.9\pm 4.9\) & \(1.1\pm 0.3\)\({}^{8}\) & & \(4.6\pm 1.4\)\({}^{8}\) & \\  & & & \(\text{KINSIM}\) & & & & & \\ \hline \hline \end{tabular}  
* For ease expressed as a multiple of body weight; \({}^{2}\) Motion capturing system; \({}^{3}\) Force plate; \({}^{4}\) Electro myography; \({}^{5}\) Pressure-sensitive map; \({}^{6}\) Fluoroscopic imaging; \({}^{7}\) Kinematic simulation; \({}^{8}\) Estimated from graph \({}^{9}\) PSM for measuring thigh-calf contact force was used in a separate measurement.  
\end{table} 
Table 3: Comparison of cited studies that investigated knee joint forces during kneeling and squatting postures—means and standard deviation. during deep squatting and deep kneeling these forces are critically dependent on the soft-tissue contact forces at the posterior surface of the leg [23; 24]. Our study indicates that approximately 85% of the relevant ground reaction force is compensated for by the thigh-calf contact. These boundary conditions drastically reduced the knee flexion moment and the consequent quadriceps muscle force, which are seen as a requirement for sustaining squatting and deep kneeling postures. [PERSON] et al. [22] reported averaged thigh-calf contact forces of between 62 and 68% of the ground reaction force of one leg for deep kneeling and squatting, assuming an equal load distribution between the two legs. Considering their observation of a significant load shift to the dominant leg of approximately 20%, the soft-tissue contact forces yield 74 to 82% of the relevant ground reaction force. By applying these averaged thigh-calf contact forces to a simulated downward squatting movement, [PERSON] et al. [23] calculated tibiofemoral compressive joint forces of 2.9 BW and patella ligament forces of almost the same magnitude. This would correspond to a quadriceps force of 4.3 BW when applying the patellar model used in the present study.