Dynamic imaging to guide wearable robotic intervention for enhanced mobility in aging

摘要 老年人比年轻人走得更慢，代谢能量消耗更高，这些变化减少了 独立性和生活质量。这些功能障碍源于踝关节推力的急剧减少 传统力量训练无法提高的功率输出。越来越多的证据表明 根据小腿三头肌 (TS) 肌肉肌腱结构特性调整的肌肉激活模式有助于 蹬地过程中踝关节力量输出的有效爆发。这项研究解决了两个关键问题：（1）年龄- 系列弹性跟腱 (AT) 结构特性（即刚度，kT）的相关变化会扰乱调谐 具有级联代谢惩罚的 TS 的神经机械功能？ (2) 是否可以佩戴松紧带 外骨骼与生物 TS 肌腱平行，改变结构刚度并改善 老年人行走的神经力学和能量消耗？具体目标 1 将量化衰老的影响 小腿三头肌-跟腱相互作用动力学的激活依赖性调节。使用受控的 测功机上的负荷和跑步机行走期间的生理负荷，我们将结合先进的双探头 利用新型肌电生物反馈对 TS 肌束和局部 AT 组织进行电影超声成像 评估肌肉与肌腱（kM 和 kT）对整体 TS 肌肉肌腱硬度 (kMT) 的个体贡献 全面了解肌肉激活情况。结合代谢测量，我们将检验假设 (1A) 老年人比年轻人有更多的 AT 抱怨（即较低的 kT），因此，(1Bi) 在孤立的情况下 肌肉在规定的 TS 肌肉激活时收缩，老年人在较短的 TS 肌束下进行操作 (1Bii) 在以匹配的速度行走期间，为了保持总体 kMT，老年人会增加 通过转移到比年轻人更短的肌束长度更高的激活来提高 TS 肌肉硬度（即更高的 kM） 成人 - 对 (1) 个体 TS 肌肉（每单位激活力）和 (b) 整体具有能量影响 - 身体（步行经济）水平。具体目标 2 将确定弹性踝关节外骨骼如何改变 老年人行走的神经力学和能量学——从全身到个体肌肉。使用 新型踝关节外骨骼模拟器，我们将应用一系列与 TS 肌肉平行的外肌腱 (kEXO) 肌腱（kMT），而老年人以固定的跑步机速度行走。我们将检验以下假设：(2A) 老年人 使用弹性踝关节外骨骼将表现出 TS 肌肉激活减少和 TS 肌束更长 操作长度，以及 (2B) 对于老年人，kEXO 最接近地使 TS 肌肉肌腱硬度正常化 (kMT) 与其体型匹配的年轻同行将产生最年轻的步行表现， 证据如下：(i) 脚踝蹬地功率输出的最大增加和 (ii) 代谢能量的最大减少 成本。最终，这项工作将建立一个使用超声成像指导最佳处方的框架 可以有效改变踝关节小腿三头肌肌腱结构以改善的辅助器具 衰老过程中的运动功能——这一结果将对数百万人的生活质量产生重大积极影响。

ABSTRACT Older adults walk slower and with higher metabolic energy cost than younger adults, changes that reduce independence and quality of life. These functional impairments stem from precipitous reductions in ankle push- off power output that cannot be improved by conventional strength training. Growing evidence reveals that muscle activation patterns tuned to underlying triceps surae (TS) muscle-tendon structural properties facilitate an effective burst of ankle power output during push-off. This study addresses two key questions: (1) Do age- related changes in series-elastic Achilles tendon (AT) structural properties (i.e., stiffness, kT) disrupt the tuned neuromechanical function of the TS with cascading metabolic penalties? and (2) Can donning elastic exoskeletons in parallel with biological TS muscle-tendons alter structural stiffness and improve the neuromechanics and energy cost of walking in older adults? Specific Aim 1 will quantify how aging effects activation-dependent tuning of triceps surae muscle-Achilles tendon interaction dynamics. Using controlled loads on a dynomometer and physiological loads during treadmill walking, we will couple advanced, dual-probe cine ultrasound imaging of TS muscle fascicles and localized AT tissue with novel electromyographic biofeedback to assess individual contributions of muscle versus tendon (kM and kT) to overall TS muscle-tendon stiffness (kMT) over a full landscape of muscle activation. Combined with metabolic measurements, we will test the hypotheses that (1A) older adults have a more complaint AT (i.e., lower kT) than young adults and thus, (1Bi) in isolated muscle contractions at prescribed TS muscle activations, older adults operate at shorter TS muscle fascicle lengths, and (1Bii) during walking at matched speeds, in an attempt to maintain overall kMT, older adults increase TS muscle stiffness (i.e., higher kM) by shifting to higher activations with shorter fascicle lengths than young adults -- with energetic implications at the (1) individual TS muscle (force per unit activation) and (b) whole- body (walking economy) levels. Specific Aim 2 will determine how elastic ankle exoskeletons alter the neuromechanics and energetics of walking in older adults – from whole-body to individual muscles. Using a novel ankle exoskeleton emulator we will apply a range of exo-tendons (kEXO) in parallel with the TS muscle- tendon (kMT) while older adults walk at a fixed treadmill speed. We will test the hypotheses that (2A) older adults using elastic ankle exoskeletons will demonstrate reduced TS muscle activation and longer TS muscle fascicle operating lengths, and (2B) for older adults, the kEXO that most closely normalizes TS muscle-tendon stiffness (kMT) to that of their size-matched, young counterparts will yield the most youthful walking performance, evidenced by: (i) largest increase in ankle push-off power output and (ii) largest reduction in metabolic energy cost. Ultimately, this work will establish a framework for using ultrasound imaging to guide optimal prescription of assistive devices that can effectively modify the structure of the ankle triceps surae muscle-tendons to improve locomotor function in aging – an outcome that will have significant positive impact on quality of life for millions.