## 3 Results
### Joint Torques and TF Shear Force  
The knee-extension muscle torque (\(\tau_{\rm knee}>0\)) reaches considerably high values (about 250 Nm) when \(y_{\rm wall}=y_{\rm hip}\) and \(d=50\) cm, at the higher knee flexion angles \((\theta_{\rm knee}\ \sim\ 77^{\circ})\) that can be reached in this condition (Figure 3). \(\tau_{\rm knee}\) is an increasing function of \(d\) for \(y_{\rm wall}=y_{\rm hip}\), whereas it becomes a decreasing function of \(d\) for \(y_{\rm wall}=y_{\rm shoulder}\). Near full knee extension, a knee-flexion muscle torque \((\tau_{\rm knee}<0)\) has to be developed to hold a static wall-squat position with scapular support (\(y_{\rm wall}=y_{\rm shoulder}\)), and even with pelvic support (\(y_{\rm wall}=y_{\rm hip}\)) as long as \(x_{\rm GR}=x_{\rm ankle}+13\ {\rm cm}\). The peak value of knee-flexion torque (\(-65\) Nm) is reached for \(y_{\rm wall}=y_{\rm shoulder}\), \(x_{\rm GR}=x_{\rm ankle}+13\ {\rm cm}\), \(d=50\) cm, and \(\theta_{\rm knee}=180^{\circ}\).  
Figure 3: Dependence of the knee muscle torque \(\tau_{\rm knee}\) on the knee angle \(\theta_{\rm knee}\) for different values of the horizontal ankle-to-hip distance \(d\) (\(d=0.2\), 0.3, 0.4, 0.5 m), two positions of the centre of pressure \(y_{\rm wall}\) of the force exerted by the wall on the back (scapular support, \(y_{\rm wall}=y_{\rm shoulder}\), and pelvic support, \(y_{\rm wall}=y_{\rm hip}\)), and two positions of the centre of pressure \(x_{\rm GR}\) of the ground reaction force (\(x_{\rm GR}\) at rearfoot, \(x_{\rm GR}=x_{\rm ankle}\), and \(x_{\rm GR}\) at forefoot, \(x_{\rm GR}=x_{\rm ankle}+13\ {\rm cm}\)). Positive values of \(\tau_{\rm knee}\) reflect a knee-extension muscle torque, whereas negative values reflect a knee-flexion muscle torque. Data refer to a subject 175 cm tall with a body mass of 75 kg.  
For \(y_{\rm wall}=y_{\rm hip}\), the hip-extension muscle torque \(\tau_{\rm hip}\) turns out to be negligible (\(\tau_{\rm hip}~{}\sim~{}0\)). However, \(\tau_{\rm hip}\) reaches values of about 130 Nm for \(y_{\rm wall}=y_{\rm shoulder}\), \(x_{\rm GR}=x_{\rm ankle}+13\) cm, \(d=50\) cm, and \(\theta_{\rm knee}~{}\sim~{}80^{\circ}\) (Figure 4). In this condition \(\tau_{\rm knee}\) is as low as 30 Nm.  
For \(x_{\rm GR}=x_{\rm ankle}\), the ankle muscles always develop a dorsiflexion torque (\(\tau_{\rm ankle}<0\)), and \(|\tau_{\rm ankle}|\) is an increasing function of \(d\) and a decreasing function of \(\theta_{\rm knee}\) and \(y_{\rm wall}\) (Figure 5). Conversely, for \(x_{\rm GR}=x_{\rm ankle}+13\) cm, \(\tau_{\rm ankle}\) is of plantar flexion type (\(\tau_{\rm ankle}>0\)), and becomes a decreasing function of \(d\) and an increasing function of \(\theta_{\rm knee}\) and \(y_{\rm wall}\). In both cases, \(|\tau_{\rm ankle}|\) reaches a maximum value of about 40 Nm.  
Figure 4: Dependence of the hip muscle torque \(\tau_{\rm hip}\) on the knee angle \(\theta_{\rm knee}\) for different values of the horizontal ankle-to-hip distance \(d\) (\(d=0.2\), 0.3, 0.4, 0.5 m), scapular support ( \(y_{\rm wall}=y_{\rm shoulder}\)), and two positions of the centre of pressure \(x_{\rm GR}\) of the ground reaction force (\(x_{\rm GR}\) at rearfoot, \(x_{\rm GR}=x_{\rm ankle}\), and \(x_{\rm GR}\) at forefoot, \(x_{\rm GR}=x_{\rm ankle}+13\) cm). \(\tau_{\rm hip}~{}\sim~{}0\) for \(y_{\rm wall}=y_{\rm hip}\) (pelvic support). Positive values of \(\tau_{\rm hip}\) reflect a hip-extension muscle torque, whereas negative values reflect a hip-flexion muscle torque. Data refer to a subject 175 cm tall with a body mass of 75 kg.  
Figure 5: _Cont._  
Table 1 displays the maximum values of the joint torques and the corresponding exercise conditions.