Post-Stroke Contributors to Increased Energetic Cost and Decreased Gait Stability

描述 在中风等神经损伤后，功能活动往往受到限制。活动能力降低的一个潜在原因是步态稳定性降低，中风后摔倒的风险增加就是明证。活动减少的第二个潜在原因是步行的能量成本增加，再加上心血管容量的减少，可能会导致限制活动的疲劳。该项目提出，中风后步态稳定性的降低和能量消耗的增加都可以部分归因于感觉运动整合的改变，这表明准确控制随意运动的能力降低。准确的运动控制需要产生预期的肌肉激活模式的能力(驱动准确性)和使用外围反馈感知运动身体部分的机械状态的能力(感觉准确性)，这两种能力在中风后通常都会降低。拟议的实验将根据机械模型的预测，测试控制精度的降低是否会影响稳定性和能源成本。这项拟议项目的第一个目标是确定中风后控制精度降低对侧向步态稳定性的影响。简单的力学模型预测，在小扰动作用下，矢状面GAI稳定性可以被动维持，但锋面稳定性需要主动控制。保持横向稳定性的最简单的控制策略是不要选择适当的摆动腿的内侧脚放置，较多的外侧脚放置需要较少的精确控制。拟议中的实验将测试控制精度降低是否可以解释中风后额面力学的改变。这些实验的主要预期结果是，向经历过中风的人提供增强的感觉反馈将恢复更典型的步态模式，这一发现具有明确的临床意义。拟议项目的第二个目标是量化有限的控制精度对中风后增加的运动能量成本的贡献。在典型的步态中，通过在弹性跟腱中储存和返回机械能量来改善能量经济性，从而允许强大的推力，而不需要大量的趾屈肌工作。同样，弹跳的能量需求可以通过利用肌腱弹性而大大减少，而与步行相比，这项任务的简单性使系统力学的量化变得容易。拟议的实验将量化以下因素对弹跳效率的影响：1)改变机械组织特性，特别是减少 肌腱僵硬；2)肌肉将代谢能转化为机械能的效率发生变化；3)无法利用感觉反馈识别最佳运动模式。主要的预期结果是，中风后，患者将无法识别利用系统力学最佳优势的运动模式。通过选择非最优的运动方式，会增加能量成本。

DESCRIPTION Following a neurological injury such as a stroke, functional mobility is often limited. One potential cause of reduced mobility is decreased gait stability, as evidenced by the increased risk of falls after a stroke. A second potential cause of reduced mobility is an increased energetic cost of walking, which in combination with reduced cardiovascular capacity can lead to activity-limiting fatigue. This project proposes that both the decreased gait stability and increased energetic cost seen after a stroke can be partially attributed to altered sensorimotor integration, as indicated by a decreased capacity to accurately control voluntary movement. Accurate motor control requires the ability to produce the intended muscle activation pattern (actuation accuracy) and the ability to sense the mechanical state of the moving body segment using feedback from the periphery (sensation accuracy), both abilities which are commonly reduced after a stroke. The proposed experiments will test whether reductions in control accuracy affect stability and energetic cost, based on the predictions of mechanical models. The first objective of the proposed project is to identify the effects of reduced control accuracy on lateral gait stability following a stroke. Simple mechanical models predict that sagittal plane gai stability can be maintained passively in response to small perturbations, but frontal plane stability requires active control. The simplest control strategy to maintain lateral stability is t choose an appropriate mediolateral foot placement of the swing leg, with more lateral foot placement requiring less accurate control. The proposed experiments will test whether decreased control accuracy explains altered frontal plane mechanics following a stroke. The primary anticipated result of these experiments is that delivering enhanced sensory feedback to persons who have experienced a stroke will restore a more typical gait pattern, a finding with clear clinical implications. The second objective of the proposed project is to quantify the contribution of limited control accuracy to the increased energetic cost of movement following a stroke. In typical gait, energetic economy is improved by storing and returning mechanical energy in the elastic Achilles tendon, allowing strong push-off without requiring large amounts of plantarflexor muscle work. Similarly, the energetic demand of bouncing can be substantially reduced by taking advantage of tendon elasticity, while the simplicity of the task in comparison to walking eases quantification of system mechanics. The proposed experiments will quantify the effect on bouncing efficiency of: 1) altered mechanical tissue properties, specifically reduced tendon stiffness; 2) changes in efficiency of the muscular conversion of metabolic energy to mechanical energy; 3) an inability to identify the optimal movement pattern using sensory feedback. The primary anticipated result is that following a stroke, patients will be unable to identify the pattern of movement that takes optimal advantage of system mechanics. By choosing a non-optimal movement pattern, energetic cost will be increased.