Bair Woei-Nan, Prettyman Michelle G, Beamer Brock A, Rogers Mark W
Department of Physical Therapy and Rehabilitation Science, School of Medicine, University of Maryland, Baltimore, Baltimore, MD 21201, USA.
Division of Gerontology & Geriatric Medicine, VAMC GRECC, Baltimore, MD 21201, USA.
Clin Biomech (Bristol). 2016 Jul;36:74-82. doi: 10.1016/j.clinbiomech.2016.04.015. Epub 2016 Apr 29.
Protective stepping evoked by externally applied lateral perturbations reveals balance deficits underlying falls. However, a lack of comprehensive information about the control of different stepping strategies in relation to the magnitude of perturbation limits understanding of balance control in relation to age and fall status. The aim of this study was to investigate different protective stepping strategies and their kinematic and behavioral control characteristics in response to different magnitudes of lateral waist-pulls between older fallers and non-fallers.
Fifty-two community-dwelling older adults (16 fallers) reacted naturally to maintain balance in response to five magnitudes of lateral waist-pulls. The balance tolerance limit (BTL, waist-pull magnitude where protective steps transitioned from single to multiple steps), first step control characteristics (stepping frequency and counts, spatial-temporal kinematic, and trunk position at landing) of four naturally selected protective step types were compared between fallers and non-fallers at- and above-BTL.
Fallers took medial-steps most frequently while non-fallers most often took crossover-back-steps. Only non-fallers varied their step count and first step control parameters by step type at the instants of step initiation (onset time) and termination (trunk position), while both groups modulated step execution parameters (single stance duration and step length) by step type. Group differences were generally better demonstrated above-BTL.
Fallers primarily used a biomechanically less effective medial-stepping strategy that may be partially explained by reduced somato-sensation. Fallers did not modulate their step parameters by step type at first step initiation and termination, instances particularly vulnerable to instability, reflecting their limitations in balance control during protective stepping.
外部施加的侧向扰动引发的保护性跨步揭示了跌倒背后的平衡缺陷。然而，缺乏关于不同跨步策略的控制与扰动幅度之间关系的全面信息，限制了对与年龄和跌倒状态相关的平衡控制的理解。本研究的目的是调查老年跌倒者和非跌倒者在应对不同幅度的侧向腰部拉力时的不同保护性跨步策略及其运动学和行为控制特征。
52名社区居住的老年人（16名跌倒者）对五种幅度的侧向腰部拉力做出自然反应以维持平衡。比较了跌倒者和非跌倒者在平衡耐受极限（BTL，保护性跨步从单步转变为多步时的腰部拉力幅度）及以上时，四种自然选择的保护性跨步类型的第一步控制特征（跨步频率和步数、时空运动学以及着陆时的躯干位置）。
跌倒者最常采取内侧跨步，而非跌倒者最常采取交叉后退步。只有非跌倒者在跨步起始（开始时间）和终止（躯干位置）瞬间根据跨步类型改变步数和第一步控制参数，而两组均根据跨步类型调节步执行参数（单支撑持续时间和步长）。组间差异在BTL以上时通常表现得更明显。
跌倒者主要采用生物力学上效果较差的内侧跨步策略，这可能部分归因于躯体感觉的降低。跌倒者在第一步起始和终止时，即在特别容易出现不稳定的情况下，不会根据跨步类型调节步参数，这反映了他们在保护性跨步过程中平衡控制的局限性。
