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

项目摘要 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。 生活保持平衡的能力，以应对意外的扰动，如颠簸，绊倒或不平衡 地形是健康移动的关键组成部分。然而，老年人这样做的能力降低， 增加了跌倒的风险。尽管许多训练方法旨在提高适应能力， 扰动，结果是高度可变的。部分原因可能是培训对象不合适。 快速且适当地产生校正扭矩以响应于压力而保持平衡的能力。 扰动由神经和生物力学因素介导。踝关节在全身反应中至关重要 扰动，因为它产生校正扭矩的大部分。对抗扰动的踝关节力矩 由踝关节的阻抗引起，施加的位移和合成位移之间的关系 扭矩和神经介导的肌肉激活变化。反应时间增加， 老年人的肌肉肌腱特性与反应能力受损有关。然而，在这方面， 这些变化对扰动反应的相对重要性仍然未知。 这项建议将集中在确定踝关节阻抗和反应时间的相对贡献， 抵抗姿势扰动的能力。阻抗直接与材料的机械性能有关。 跨越关节的结构（即肌肉、肌腱、韧带）。虽然肌肉肌腱的年龄依赖性变化 虽然这些属性应该会影响踝关节阻抗，但其影响的大小仍然未知。这是一个关键 理解它们对改变运动性能的贡献存在障碍。目标1将确定是否有年龄- 踝阻抗的依赖性变化，并量化其幅度。踝关节、肌肉和肌腱贡献 阻抗将使用一种新的技术进行量化，该技术采用踝关节力学的机器人评估， 肌肉和肌腱运动的超声成像。这些结构的阻抗将使用系统 识别.这种同时进行的评估对于确定肌肉的机械性能如何至关重要。 和肌腱对踝关节的力学有贡献。目标2将确定踝关节阻抗 和反应时间有助于对姿势扰动的反应的年龄相关差异。踝关节姿势 当受试者平衡一个虚拟的倒立摆时， 模拟站立时产生的踝关节负荷。业绩将通过平衡能力来量化 钟摆不同的条件将被用来区分踝阻抗和反应时间的影响 任务表现。总之，这项工作的结果将提供深入了解损害老年人的机制， 成年人对意外姿势扰动的反应能力。这一定量评估对于 针对特定主题优化旨在增强老年人活动能力的训练方案。

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.