# Postural Instability after Stepping on a Stair in Older Adults: A Pilot Study
## 4 Discussion  
There have been only a few studies using time to stabilization (TTS) to assess postural capacity in older adults (OA) or disease populations. A previous study utilized TTS to assess how stroke patients control their postural stability in response to unpredicted perturbation [17]. They reported that stroke patients who had intensive weighted training showed decreased TTS scores, indicating their improved capacity to stabilize their postural sway in the face of unpredicted perturbations. [PERSON] and [PERSON] [18] further demonstrated that an improvement in one's postural stability as measured by TTS was observed more in older adults who had exercise training than those without training. To our knowledge, this preliminary investigation is the first to assess the stabilization capacity of OA following a stepping movement, as measured by TTS. There have been a \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Variables** & **Older Adults (OA)** & **Young Adults (YA)** & \(p\)**-Value** \\ \hline Time to Stabilization (AP) & 1.62 \(\pm\) 0.15 & 1.26 \(\pm\) 0.12 & \(p\) = 0.032 \({}^{*}\) \\ Time to Stabilization (ML) & 1.85 \(\pm\) 0.21 & 1.82 \(\pm\) 0.23 & \(p\) = 0.141 \\ COPVEL (cm/s) & 0.84 \(\pm\) 0.23 & 0.81 \(\pm\) 0.25 & \(p\) = 0.455 \\ COPSWAY (CE95\%, cm\({}^{2}\)) & 31.4 \(\pm\) 12.1 & 0.81 \(\pm\) 0.25 & \(p\) = 0.176 \\ \hline \hline \end{tabular} \({}^{*}\) Significant difference between OA and YA at \(p\) < 0.05.  
\end{table} 
Table 1: Mean, standard deviation, and \(p\)-value from \(t\)-tests for all dependent variables, including TTS AP, TTS ML, COPVEL, and COPSWAY. \(p\) < 0.05 for difference between OA and YA. Figure 3: The center of pressure (COP) trajectories during posture stabilization after a stepping movement in OA and YA. few studies that have compared spatiotemporal measures and the stabilizing strategies of OA and YA during stair ascent. One study reported that there were no significant group differences in stepping performance [19], while another study reported that OA show smaller separations between the center of mass and the center of pressure, which is indicative of different stepping strategies between groups [20]. However, no study examined the stabilization capacity after the stepping movement had been completed. By using TTS in this study, we tried to account for the deficits of stabilizing capacity in OA during a challenging dynamic movement. As hypothesized, OA exhibited a significantly longer time to stabilize their postural sway following stair ascent in comparison to YA. This finding indicated that OA may have less capacity to regain postural stability compared to YA following a challenging task, such as stepping on a stair. Given that a longer time for stabilization is highly correlated with a greater risk of falls [21], our TTS finding supports the observation that OA are at a greater risk of falls compared to YA. The finding of the current study could potentially provide a reliable and objective index for the evaluation of dynamic postural stability in OA. However, we did not observe any significant differences between OA and YA in balance performance during posture stabilization after stepping on a stair when we assessed this using COP measures (e.g., COPVEL and COPSWAY). Conventionally, balance problems in OA have been identified by evaluating the COP motion [22]. For example, greater velocity or sway area during static movement has been considered to be one of the representative characteristics of postural control deficits in OA [23]. Biomechanically, however, dynamic movement, such as stair ascent, require a sufficient level of body momentum and co-contraction between COP and the body's center of mass to maintain postural stability when compensating for propulsive body momentum [24].