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

摘要 老年人走得慢，代谢能量消耗比年轻人高， 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- 关闭功率输出，不能通过传统的力量训练提高。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 在蹬地过程中有效爆发踝关节动力输出。本研究解决了两个关键问题：（1）年龄- 串联弹性跟腱（AT）结构特性的相关变化（即，刚度，kT）破坏调谐 神经机械功能的TS级联代谢处罚？（2）可穿松紧带 外骨骼与生物TS肌肉-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将量化衰老如何影响 小腿三头肌肌肉-跟腱相互作用动力学的激活依赖性调谐。使用受控 在跑步机行走过程中，我们将结合先进的双探头 应用新型肌电生物反馈对TS肌束和AT组织进行电影超声成像 评估肌肉与肌腱（kM和kT）对总体TS肌肉-肌腱刚度（kMT）的个体贡献 在一个完整的肌肉激活的景观。结合代谢测量，我们将检验假设 （1A）老年人有更多的抱怨AT（即，较低的kT）比年轻的成年人，因此，（1Bi）在孤立的 肌肉收缩在规定的TS肌肉激活，老年人在较短的TS肌束操作 长度，（1Bii）在以匹配的速度行走时，为了维持整体kMT，老年人增加 TS肌肉僵硬（即，更高的kM）通过转移到更高的激活与更短的束簇长度比年轻 成年人-在（1）个体TS肌肉（每单位激活的力）和（B）整体上具有能量暗示- 身体（步行经济）水平。具体目标2将确定如何弹性踝关节外骨骼改变 老年人行走的神经力学和能量学-从全身到个体肌肉。使用 新的踝关节外骨骼模拟器，我们将应用一系列的外肌腱（kEXO）与TS肌肉平行， 肌腱（kMT），而老年人以固定的跑步机速度行走。我们将测试假设（2A）老年人 使用弹性踝关节外骨骼将显示减少的TS肌肉激活和更长的TS肌肉束 操作长度，以及（2B）对于老年人，最接近正常化TS肌肉肌腱硬度的kEXO (kMT)与他们的大小匹配，年轻的同行将产生最年轻的步行性能， 通过以下方式证明：（i）踝关节蹬离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框架，利用超声成像来指导最佳处方 的辅助装置，可以有效地修改结构的踝小腿三头肌肌腱，以改善 运动功能在老化-一个结果，将有显着的积极影响，生活质量的数百万人。

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.