Determining the neural and biomechanical contributions to age-dependent impairments in balance control

项目总结 行动不便是老年人残疾的主要原因，影响独立性和生活质量 生活。在遇到意外扰动时保持平衡的能力，如颠簸、绊倒或凹凸不平 地形是健康机动性的关键组成部分。然而，老年人这样做的能力有所降低， 增加了他们跌倒的风险。尽管许多训练方法都是为了提高适应能力 扰动，结果是高度多变的。这可能在一定程度上归因于针对性不强的培训。 快速和适当地产生校正扭矩以保持平衡的能力 扰动是由神经和生物力学因素介导的。在全身反应中，脚踝是至关重要的 当它产生校正扭矩的很大一部分时，会产生扰动。与扰动相反的踝关节扭矩 产生于脚踝的阻抗，施加的位移和由此产生的关系 扭矩，以及神经介导的肌肉激活变化。增加了反应时间，并改变了 老年人的肌腱特性与反应能力受损有关。然而， 这些变化对对扰动的反应的相对重要性尚不清楚。 这项建议将集中于确定踝关节阻抗和反应时间对 能够抵抗姿势的干扰。阻抗与材料的机械性能直接相关。 跨越关节的结构(即肌肉、肌腱、韧带)。而肌腱的年龄相关性变化 属性是否会影响脚踝阻抗，其影响的大小尚不清楚。这是一个关键的 理解它们对改变运动性能的贡献的障碍。目标一号将确定是否存在年龄- 踝关节阻抗的依赖性变化，并量化其大小。脚踝、肌肉和肌腱的贡献 将使用一种新的技术来量化TO阻抗，该技术使用机器人评估脚踝力学和 肌肉和肌腱运动的超声成像。这些结构的阻抗将使用系统进行量化 身份证明。这种同步评估对于确定肌肉的机械性能如何 和肌腱对脚踝的力学有贡献。目标2将确定脚踝阻抗的程度 反应时间对姿势干扰反应的年龄相关差异有贡献。脚踝姿势 当受试者平衡一个虚拟倒立摆时，会意外地被机器人设备扰乱 模拟站立过程中产生的脚踝载荷。表现将通过平衡的能力来量化 钟摆。将使用不同的条件来区分脚踝阻抗和反应时间的影响 在任务表现上。总之，这项工作的结果将为老年人受损的机制提供洞察力 成年人对意想不到的姿势扰动的反应能力。这一量化评估对于 针对具体科目优化培训方案，旨在提高老年人的行动能力。

PROJECT SUMMARY Impaired mobility is the leading cause of disability among older adults, impacting independence and quality of life. The ability to maintain balance in response to unexpected perturbations such as a bump, trip, or uneven terrain is a critical component of healthy mobility. Older adults, however, have a reduced capacity to do so, increasing their risk of falling. Despite many training methods aimed at improving the ability to adapt to perturbations, outcomes are highly variable. This may be due, in part, to improperly targeted training. The ability to rapidly and appropriately generate a corrective torque to maintain balance in response to a perturbation is mediated by neural and biomechanical factors. The ankle is critical in the response to whole-body perturbations as it generates a substantial portion of the corrective torque. Ankle torques opposing a perturbation arise from the impedance of the ankle, the relationship between imposed displacements and the resultant torques, and neurally-mediated changes in muscle activation. Increased reaction times and altered musculotendon properties in older adults have been associated with an impaired ability to respond. However, the relative importance of these changes to the response to perturbations remains unknown. This proposal will focus on determining the relative contributions of ankle impedance and reaction time to the ability to resist perturbations of posture. Impedance is directly related to the mechanical properties of the structures spanning the joint (i.e. muscle, tendon, ligaments). While age-dependent changes in musculotendon properties should impact ankle impedance, the magnitude of their effect remains unknown. This is a critical barrier to understanding their contributions to altered motor performance. Aim 1 will determine if there are age- dependent changes in ankle impedance and quantify their magnitude. Ankle, muscle, and tendon contributions to impedance will be quantified using a novel technique employing robotic assessments of ankle mechanics and ultrasound imaging of muscle and tendon motions. Impedance of these structures will be quantified using system identification. This simultaneous assessment is vital for determining how the mechanical properties of the muscle and tendon contribute to the mechanics of the ankle. Aim 2 will determine the extent to which ankle impedance and reaction time contribute to age-related differences in the response to postural perturbations. Ankle posture will be unexpectedly perturbed using a robotic device as the subject balances a virtual inverted pendulum simulating the ankle loads generated during standing. Performance will be quantified by the ability to balance the pendulum. Different conditions will be used to differentiate the impact of ankle impedance and reaction time on task performance. Together, the results from this work will provide insight to the mechanism impairing older adults’ ability to respond to unexpected postural perturbations. This quantitative assessment is vital for the subject-specific optimization of training protocols aimed at enhancing mobility in the elderly.