## 3 Results  
The study involved five subjects, three females and two males (age 34.2 \(\pm\) 10.3 years, mass 60.0 \(\pm\) 6 kg, mean \(\pm\) SD). For the validation of the model, we used the data of a woman from the \"_Third Grand Challenge Competition to predict in vivo knee loads_\" [26]. Each subject performed 5 continuous cycles for each of the three loading conditions (no load, L0; 6 kg load, L1; and 12 kg load, L2). Only measurements for the right leg were recorded. Table 1 shows the kinematic characteristics of the movements (mean and SD) of the knee range (flexion-extension), and the corresponding maximum angular velocities in both directions. The mean range of flexion was 96.2\({}^{\circ}\), with a maximum value of 106.5\({}^{\circ}\). The mean maximum angular velocity was 81.2\({}^{\circ}\)/s in the flexion movement and somewhat faster (86.4\({}^{\circ}\)/s) in the extension movement. Table 2 describes the dynamic variables estimated by the full dynamic model (FDM). Knee moment had a negative mean value in the order of \(-\)30 Nm, with a maximum value of 11.1 Nm. It was negative during most of the movement, and needed to be balanced by the extensor muscles. As a result, the vastus lateralis muscle was active during most of the movement, exerting an average force of 275 N and a maximum value of 680 N. In the same way, the average and maximum forces induced by the vastus medialis were 118 N and 290 N, respectively. With respect to the reaction forces on the tibial plateau, the mean normal compressive force was 1000 N, and its maximum value was almost doubled, 1974 N. The forces in the tangential direction had much lower values (mean: 90 N; maximum: 350 N). The great dispersion of the forces obtained in the different tests should be noted. This may be due to differences between subjects and between load conditions. The knee angle showed, on average, 99.2% of the variance of the other generalized coordinates (98.5% for the lowest quartile). This result confirms to the hypothesis that the movement has a single functional degree of freedom. Hence, it will be possible to estimate all generalized coordinates from the knee angle. The correspondence between the FDM and SGM models is almost perfect (Table 3). The value of the ICC was 1.000 and the error resulting from neglecting the inertial forces is insignificant (less than 0.1% of the total range). The effect of the gravitational parameters on the estimation of forces is also limited, and hardly represents an average difference of the order of 1% of the range. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Variable** & **Mean** & **STD** \\ \hline Knee ROM (\({}^{\circ}\)) & 96.2 & 7.1 \\ Max knee flexion angle (\({}^{\circ}\)) & 106.5 & 5.9 \\ Max flexion angular velocity (\({}^{\circ}\)/s) & 81.2 & 25.0 \\ Max extension angular velocity (\({}^{\circ}\)/s) & 81.2 & 22.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Kinematic characteristics of the movements (\(n=15\), five subjects x three load conditions). Figure 4 illustrates these results for a specific subject, showing the contributions of each component of the dynamic model to the generalized forces. As can be seen, the most important component is the external force on the foot. The force of gravity has a minor effect. The effect of the inertial components is negligible. Table 4 shows [PERSON]'s correlation coefficients between EMG signals as measured for the vastus medialis and vastus lateralis muscles, and the corresponding muscle force values as estimated by the SGM. Flexion and extension motions were separated for each cycle. We used 75 records for the flexion direction and the same number for the extension direction (five subjects, three trials, five cycles).