# Study of Force Changes Based on Orthotic Elements Under the First Ray
## 3 Results  
A total of 22 feet (N = 22) from the dominant lower limbs of 22 participants were analyzed, comprising 12 women and 10 men, with a mean age of 28.9 years and a mean body mass index (BMI) of 24.1 (Table 1). A multivariate linear regression analysis was performed to evaluate whether the descriptive variables (age, sex, weight, height, BMI, shoe size, and foot posture index) could act as potential confounding factors affecting the ground reaction force components. This analysis was conducted across all orthotic conditions and for each force direction (Fx, Fy, and Fz), during both the mid-stance and propulsion phases. As shown in Table 2, most of the coefficients of determination (R\({}^{2}\)) ranged from 0 to below 0.5. Considering practical thresholds for identifying confounding factors (e.g., r \(\geq\) 0.5), the observed values generally fell short of this criterion, except for FxG2 in condition C (R\({}^{2}\) = 0.507) and FyG1 in condition F (R\({}^{2}\) = 0.515). The majority of the R\({}^{2}\) values were closer to 0.2-0.3, implying correlation coefficients well below 0.5 (e.g., r \(\approx\) 0.45 or lower). Although these two specific variables showed R\({}^{2}\) values slightly above 0.5, they did not exhibit statistically significant correlations with any of the descriptive variables in any condition. As such, their potential as confounding factors was considered negligible and does not affect the main findings of the study. We therefore found no statistical evidence to support the presence of confounding variables. \begin{table}
\begin{tabular}{l c c c} \hline  & **Mean \(\pm\) SD** & **Median** & **RIQ** \\ \hline Age (years) & 28.9 \(\pm\) 10.6 & 24.5 & 22.8–28.5 \\ Body mass (kg) & 70.5 \(\pm\) 16.2 & 67.0 & 59.5–82.3 \\ Height (m) & 1.70 \(\pm\) 0.09 & 1.70 & 1.63–1.78 \\ BMI (kg/m\({}^{2}\)) & 24.1 \(\pm\) 4.1 & 23.3 & 21.8–25.9 \\ Shoe size & 40.5 \(\pm\) 3.0 & 40.5 & 38–43 \\ FPI & 3.6 \(\pm\) 3.1 & 4 & 2–6 \\ \hline \end{tabular} Abbreviations: kg, kilogram; m, meter; m\({}^{2}\), square meter; SD, standard deviation; RIQ, interquartile range.  
\end{table} 
Table 1: Main characteristics of total sample. As shown in Table 3, the greatest vertical forces during propulsion (FzG2) were observed under the no-orthosis (WFO) condition (109.3%), followed by orthoses F (105.6%) and B (104.6%), reflecting greater loading during push-off. For antero-posterior forces (Fy) in mid-stance (FyG1), the greatest propulsive forces were registered with orthoses E (9.2%) and B (8.9%). Regarding medio-lateral forces (Fx) during propulsion (FxL2), condition B showed the most lateral deviation (-2.9%), while condition A exhibited the least (-1.7%), suggesting better medial stabilization. Table 4 displays the correlations between the ground reaction force components (Fx, Fy, and Fz) and the participant variables (age, BMI, shoe size, and foot posture index, FPI) across various orthotic conditions and gait phases. Significant negative correlations were found between the FPI and the medio-lateral force (Fx) during late stance (L2) for orthoses B, C, D, E, and F (r values between \(-\)0.436 and \(-\)0.608; \(p\) < 0.05), indicating increased lateral shifts in more pronated feet. The FPI also showed significant positive correlations with the vertical force (Fz) for orthosis B during mid-stance and propulsion, and for orthosis E during mid-stance. Fy was positively correlated with the FPI only in orthosis B during mid-stance. The BMI was negatively associated with Fz for WFO (G2) and orthosis F (L2).