Step initiation characteristics in dementia patients

The early identification of balance disorders and their appropriate interpretation is crucial for dementia patients. The aim of this study was to identify postural instability in dementia patients with mild to moderate stage and control group during step initiation under different conditions. 54 dementia patients and thirty age-matched healthy controls voluntarily participated in the study. Step initiation was performed on two force plates under four conditions: unperturbed transition between platforms, obstacle clearance, step-up and step-down. The trials were repeated 3 times and lasted 35 s each. Recordings of center-of-foot pressure displacements were divided into three distinct phases: 1st phase – quiet standing before step initiation, 2nd phase – transit, and 3rd phase – quiet standing after step initiation. The following variables of COP displacement were calculated for the 1st and 3rd phases: the mean velocity of COP (vCOP) [cm/s] in an anterior-posterior (AP) and medio-lateral (ML) plane. In the 2nd phase, the following variables were also derived: TT (s)– transit time - the duration of the second phase, S1 (s) – first stability time - the time from exiting steady standing (beginning of phase 2) to the time when the leading foot was resting on the other platform, S2 (s) – second stability time - the time from raising the foot from the first platform to the end of the phase, DSP (s) – double-support period - when the trailing foot is touching the first platform and the leading foot is simultaneously touching the second platform during the step. Dementia patients were characterized by the longer step initiation time compared to control group under all conditions (p < 0.03). There were significant differences in quiet standing before step initiation between dementia patients and control group but only in unperturbed and obstacle clearance trials (p < 0.02). There were no significant differences in quiet standing after step transition between dementia patients and control group (p > 0.05). The new proposed objective method is a reliable tool for detecting differences between mild and moderate stages of dementia and healthy peers, which is crucial in clinical practice. Postural control research should focus on functional motor tasks rather than simple motor tasks such as quiet standing.早期识别平衡障碍并对其进行合理判读，对于痴呆患者而言至关重要。本研究旨在探究不同条件下，轻中度痴呆患者与对照组在迈步启动过程中的姿势不稳情况。本研究共招募54名痴呆患者与30名年龄匹配的健康志愿者参与。迈步启动任务在两台测力台上开展，共设置四种实验条件：平台间无扰动转移、越障、上台阶及下台阶。每个条件下重复进行3次试次，每次试次时长为35秒。研究将足底压力中心（Center-of-foot pressure, COP）位移记录划分为三个明确阶段：第一阶段为迈步启动前的静立状态，第二阶段为转移过程，第三阶段为迈步启动后的静立状态。针对第一与第三阶段，计算COP位移的如下指标：前后轴（anterior-posterior, AP）与内外轴（medio-lateral, ML）方向上的COP平均速度（vCOP，单位：cm/s）。针对第二阶段，额外推导如下指标：TT（单位：s）即转移时间——第二阶段的总时长；S1（单位：s）即第一稳定期——从脱离静立状态（第二阶段起始）至前脚落至另一平台的时长；S2（单位：s）即第二稳定期——从抬起前脚至该阶段结束的时长；DSP（单位：s）即双支撑期——迈步过程中后脚接触原平台且前脚同时接触新平台的时段。实验结果显示，相较于对照组，痴呆患者在所有实验条件下的迈步启动时长均更长（p < 0.03）。两组仅在无扰动转移与越障试次的迈步启动前静立状态中存在显著差异（p < 0.02）；而在迈步转移后的静立状态中，两组未观察到显著差异（p > 0.05）。本研究提出的新型客观方法可作为可靠工具，用于区分轻中度痴呆患者与健康对照人群，这在临床实践中具有重要价值。姿势控制相关研究应更聚焦于功能性运动任务，而非静立这类简单运动任务。