## 4 Discussion  
This study investigated the short-term effects of the repeated exposure to trip-like perturbations on inter-segmental coordination during steady walking, as a follow-up analysis of a dataset collected for one of our recent works [9]. Here, we tested the hypothesis that, due to perturbation, a more precise control of the toe clearance (reduced MT\({}_{\text{SD}}\)) can occur, in conjunction with more effective organisation of the redundant lower limb segments, in accordance with the UCM theory. The results confirmed that, after the perturbation, the synergic covariation of segmental orientation further stabilises the MTC variability across strides. As an initial result, this study demonstrates that lower limb intersegmental coordination while walking is functionally structured to minimise the inter-stride MTC variability in accordance with the UCM theory (_Ratio_ > 1). Notably, previous authors have dealt with different performance variables related to the swinging foot, such as mediolateral \begin{table}
\begin{tabular}{c c c c c c c c} \hline \multirow{2}{*}{**Variable**} & \multicolumn{2}{c}{**Trial A**} & \multicolumn{2}{c}{**Trial B**} & \multicolumn{2}{c}{**Trial C**} & \multirow{2}{*}{\(p\)**-Values**} \\ \cline{2-3} \cline{5-8}  & **Baseline** & **Post-pert.** & **Baseline** & **Post-pert.** & **Baseline** & **Post-pert.** & \\ \hline MT\({}_{\text{av}}\) (mm) & 34.8 \(\pm\) 9.1 & 31.1 \(\pm\) 10.2 & 33.1 \(\pm\) 10.0 & 30.9 \(\pm\) 8.9 & 32.6 \(\pm\) 8.3 & 31.1 \(\pm\) 8.6 & \(\text{p}_{\text{SP}}=0.001\) \\  & & & & & & & \(\text{p}_{\text{int}}=0.197\) \\ \hline MT\({}_{\text{SD}}\) (mm) & 3.4 \(\pm\) 1.0 & 3.1 \(\pm\) 1.0 & 3.3 \(\pm\) 1.4 & 3.0 \(\pm\) 0.7 & 3.4 \(\pm\) 1.1 & 3.1 \(\pm\) 0.9 & \(\text{p}_{\text{SP}}=0.012\) \\  & & & & & & & \(\text{p}_{\text{int}}=0.795\) \\ \hline \(\sigma^{2}_{UCM}\) (rad\({}^{2}\)) & 0.16 \(\pm\) 0.24 & 0.19 \(\pm\) 0.18 & 0.11 \(\pm\) 0.14 & 0.16 \(\pm\) 0.17 & 0.13 \(\pm\) 0.18 & 0.18 \(\pm\) 0.18 & \(\text{p}_{\text{SP}}=0.159\) \\  & & & & & & & \(\text{p}_{\text{int}}=0.972\) \\ \hline \(10^{3}\times\sigma^{2}_{ORT}\) (rad\({}^{2}\)) & 0.08 \(\pm\) 0.04 & 0.11 \(\pm\) 0.08 & 0.14 \(\pm\) 0.22 & 0.13 \(\pm\) 0.15 & 0.11 \(\pm\) 0.15 & 0.09 \(\pm\) 0.06 & \(\text{p}_{\text{ST}}=0.712\) \\  & & & & & & & \(\text{p}_{\text{int}}=0.769\) \\ \hline \(10^{-3}\times\text{{Ratio}}\) (adim) & 1.58 \(\pm\) 2.06 & 2.92 \(\pm\) 3.73 & 1.56 \(\pm\) 2.45 & 2.15 \(\pm\) 3.23 & 1.65 \(\pm\) 2.62 & 2.86 \(\pm\) 4.14 & \(\text{p}_{\text{SP}}=0.015\) \\  & & & & & & \(\text{p}_{\text{int}}=0.926\) \\ \hline \end{tabular}
\end{table} 
Table 1: Independent variables (mean \(\pm\) standard deviation) as assessed across experimental conditions and outcome of the statistical analysis. Acronyms \(\text{p}_{\text{T}}\); \(\text{p}_{\text{SP}}\), \(\text{p}_{\text{int}}\) represent the outcome of the statistical analysis in terms of \(p\)-values with respect to factors trial (three levels: A, B, and C), sub-phase (two levels: baseline and post-perturbation), and their interaction, respectively. \(p\)-values are reported in bold when significant (\(p<0.05\)). footpath trajectory [26; 27; 28; 29], or whole 3D footpath [12; 24], and reported slightly discordant outcomes [12]. Our findings, in conjunction with previous ones [12; 24; 26; 27; 28; 29], suggest that the central nervous system may aim at individually and flexibly stabilising the inter-stride variability of footpath components (e.g., mediolateral, vertical) during different periods of the swing phase. This hypothesis deserves to be further investigated to gain a more general understanding concerning the organisation of inter-stride variability of lower limb body segments during the swing phase. The main result is related to the decrease in MTCD and suggests that the strength of the kinematic synergy underlying MTC stabilisation across strides further increases after the perturbation (se _Ratio_ in Table 1).