# Effects of a Dual-Task Paradigm and Gait Velocity on Dynamic Gait Stability during Stair Descent
## 3 Results  
The Shapiro-Wilk test indicated that all the dependent variables were normally distributed (\(p>0.05\)). Figure 2 presents the gait velocity magnitude traces of the different conditions. Velocity decreased from left toe-off and reached its lowest point at about 35% of the single-stance phase before increasing to a greater value. One-way repeated measures ANOVA for peak velocity revealed significant condition differences (\(p<0.001\)). Post hoc analysis indicated that the peak velocities under CT (\(p=0.003\)) and MT (\(p<0.001\)) dual-task conditions were significantly lower than that under ST (\(\text{CT}_{\text{velocity}}=0.79\pm 0.09\); \(\text{MT}_{\text{velocity}}=0.68\pm 0.08\); \(\text{ST}_{\text{velocity}}=0.91\pm 0.11\) m/s). Peak velocity was also lower in MT than in CT (\(p=0.001\)). Figure 3 presents the IA traces during stair descent. Figure 3a indicates that \(\text{IA}_{\text{A/P}}\) increased from a negative value to a positive value during the right foot single-support phase, indicating that COM was behind the COP at the beginning but ahead at the ending. An IA peak was observed during left toe contact. A repeated-measures ANOVA indicated a significant condition effect (\(p<0.001\)). Post hoc analysis revealed that the peak \(\text{IA}_{\text{A/P}}\) was less under the CT and MT dual-task conditions (\(\text{CT}_{\text{A/P}}=8.29\pm 0.82^{\circ}\), \(p=0.019\); \(\text{MT}_{\text{A/P}}=7.16\pm 0.89^{\circ}\), \(p<0.001\)) than under the ST (\(\text{ST}_{\text{A/P}}=9.05\pm 0.79^{\circ}\)). The peak \(\text{IA}_{\text{A/P}}\) was also less under MT than under CT (\(p<0.001\)). In Figure 3b, \(\text{IA}_{\text{M/L}}\) decreased from left toe-off, then increased to a much greater value during the single-support phase. A positive value indicated that the COP was lateral (on the right) to the COM. A repeated-measures ANOVA revealed a significant condition effect (\(p=0.020\)). Post hoc analysis revealed that the peak \(\text{IA}_{\text{M/L}}\) during MT (\(\text{MT}_{\text{M/L}}=5.95\pm 1.02^{\circ}\), \(p=0.020\)) was less than that during ST (\(\text{ST}_{\text{M/L}}=6.49\pm 0.53^{\circ}\)). Figure 2: Descending velocity (y) of the single-support phase (x) during single-task and cognitive and manual dual-task conditions; # Significant difference between single-task and cognitive dual-task conditions; # Significant difference between single-task and manual dual-task conditions; \(\bullet\) Significant difference between cognitive and manual dual-task conditions. During the stepwise forward elimination procedure of peak IA\({}_{\text{A/P}}\)(y) as a function of peak velocity (x), A and Ax were excluded with p-values of 0.591 and 0.645, respectively, and Bx was excluded with a VIF of 59.289. The best regression equation was expressed as follows:  
\[\text{y}=4.976+4.365\text{x}-0.768\text{B}. \tag{5}\]  
The regression determinant (r\({}^{2}\)) was 0.689 (\(p<0.001\)). The equation indicates that the faster the peak velocity, the greater the IA\({}_{\text{A/P}}\). The effect of gait velocity on IA\({}_{\text{A/P}}\) within the corresponding range of variation in this study was 2.925\({}^{\circ}\) (the difference between the maximum and minimum velocity multiplied by the regression coefficient). Concurrent MT decreased IA\({}_{\text{A/P}}\) with a magnitude of 0.768\({}^{\circ}\), whereas concurrent CT did not influence IA\({}_{\text{A/P}}\). During the stepwise forward elimination procedure of the peak IA\({}_{\text{M/L}}\) (y) as a function of peak velocity (x), A, B, Ax, and Bx were excluded with \(p\)-values of 0.674, 0.956, 0.497, and 0.921, respectively. The best regression equation was expressed as follows:  
\[\text{y}=4.115+2.712\text{x}. \tag{6}\]  
The regression determinant (r\({}^{2}\)) was 0.160 (\(p=0.005\)). The equation showed that the faster the peak velocity, the greater the IA\({}_{\text{M/L}}\). The effect of peak velocity on IA\({}_{\text{M/L}}\) within the corresponding variation range in this study was 1.817\({}^{\circ}\).