## 3 Results
### Description of Response to Perturbation for Kinematic and Kinetic Parameters-Perturbed Limb
#### 3.2.3 Kinetic Parameters  
The final step, which included the perturbed limb, was to compare the maximal and minimal values of lower limb joint torques between the young and elderly groups separately in the three Strategies and treadmill gait without perturbation (Figure 7A-D).  
In the first Strategy and during treadmill gait, all parameters' values were lower in the elderly group. For Strategy II, this trend continues for all variables except for dorsiflexion ankle torque, but the differences between the groups are not significant here. Strategy III significantly differs from the pattern. However, the differences between the groups are not statistically significant. In Strategy III, the discussed trend (lower values in the elderly group) is maintained only for the hip flexion and ankle plantarflexion torques.  
As for the kinematic parameters, the strategy with the highest number of extreme values deviating the least from those recorded for treadmill gait seems to be the one that should be adopted most often by the subjects. For this purpose, the differences between the extreme values adopted for each strategy and those for treadmill gait were counted separately in the two groups (Table 3). In the youth group, out of six differences, three were minimal, two were medium, and one was maximum for Strategy I. For Strategy II, three parameters had a mean, and three variables had maximum differences. For Strategy III: 3-minimum, 2-medium, and 1-maximum.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Ankle [deg]**} & \multicolumn{2}{c}{**Knee [deg]**} & \multicolumn{2}{c}{**Hip [deg]**} \\ \cline{2-7}  & \(\mathbf{min-pf}\) & \(\mathbf{max-df}\) & \(\mathbf{min-ext}\) & \(\mathbf{max-flx}\) & \(\mathbf{min-ext}\) & \(\mathbf{max-flx}\) \\ \hline \multicolumn{7}{c}{**Young**} \\ \hline I–n & 2.66 (min) & \(-\)3.02 (min) & 4.32 (mean) & \(-\)2.47 (min) & 5.78 (max) & 4.44 (min) \\ II–n & \(-\)6.1 (mean) & \(-\)4.64 (mean) & 4.67 (max) & 12.72 (mean) & 3.21 (min) & 11.61 (mean) \\ III–n & \(-\)9.37 (max) & \(-\)5.48 (max) & 1.64 (min) & 14.65 (max) & 3.46 (mean) & 12.6 (max) \\ \hline \multicolumn{7}{c}{**Elderly**} \\ \hline I–n & 8.66 (max) & 3.53 (min) & 6.2 (mean) & 4.46 (min) & 19.28 (max) & 15.82 (min) \\ II–n & 2.38 (mean) & 5.18 (mean) & 4.38 (min) & 10.42 (mean) & 18.32 (mean) & 26.86 (max) \\ III–n & \(-\)0.45 (min) & 6.12 (max) & 7.27 (max) & 19.42 (max) & 14.46 (min) & 23.3 (mean) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Differences between the means of the extreme values adopted in Strategies I, II, III, and those for gait on a treadmill without perturbation (n) for kinematic parameters of the perturbed limb with the indication of their spread (min, mean, max) relative to each other. For negative values, the comparison was for absolute values.  
Among older people, out of the six differences, four were minimal, one was medium, and one was maximum for Strategy I. For Strategy II, two parameters had a minimum, and four variables had an average distance from those recorded for gait without perturbation. For Strategy III, two variables had a mean dispersion, and four had a maximum one.  
Figure 7: The means and standard deviations for the joint torques curves for the perturbed limb (left) compared to those recorded during treadmill gait in a group of young (Y) and elderly (O), where: (**A**) Strategy I, (**B**) Strategy II, and (**C**) Strategy III, (**D**) Tradmill gait (reference), pf–plantarflexion, df–dorsiflexion, ext–extension, fix–flexion. The tables show the minimum and maximum values of joint torques for the three strategies and treadmill gait, as well as statistically significant differences between the groups and effect size (r). Bold font indicates that values in group O were higher than in group Y. When comparing negative values, their absolute values were considered.