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

摘要 与年轻人相比，老年人走路更慢，代谢能量成本更高，这些变化会减少 独立性和生活质量。这些功能障碍源于脚踝推力的急剧减少- 提供常规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)的肌肉-肌腱结构特性调整的肌肉激活模式有助于 推举过程中脚踝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- 串联弹性跟腱(AT)结构特性(即，刚度，KT)的相关变化扰乱了调谐 伴有级联代谢惩罚的TS的神经机械功能？和(2)可以穿上松紧带 外骨骼与生物TS肌腱平行改变结构刚度并改善 老年人步行的神经力学和能量成本？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调谐。使用受控 跑步机行走中的负荷和生理负荷，我们将结合先进的双探头 新型肌电生物反馈对TS肌束和定位AT组织的电影超声成像 评估肌肉和肌腱(KM和KT)对整体TS肌肉-肌腱硬度(KMT)的贡献 在整个肌肉激活的场景中。结合新陈代谢测量，我们将检验这些假设 老年人比年轻人有更多的主诉AT(即，较低的KT)，因此，(1B)在孤独症中 在规定的TS肌肉激活时肌肉收缩，老年人以较短的TS肌束操作 长度，和(1Bii)在以匹配的速度行走时，试图保持国民党的整体，老年人增加 通过转移到比年轻人更短的肌束长度的更高的激活程度来使肌肉僵硬(即更高的公里) 成人--在(1)个体TS肌肉(单位激活力)和(B)整体- 身体(步行经济)水平。具体目标2将确定弹性脚踝外骨骼如何改变 老年人行走的神经力学和能量学--从全身到个人肌肉。使用 新型踝关节外骨骼仿真器我们将应用一系列外肌腱(KEXO)与TS肌肉并行- 肌腱(国民党)，而老年人以固定的跑步机速度行走。我们将检验以下假设：(2)老年人 使用弹性脚踝外骨骼将显示TS肌肉激活减少和TS肌束变长 操作长度，以及(2B)对于老年人，kEXO最接近地使TS肌肉-肌腱僵硬正常化 (国民党)与他们体型相匹配的年轻同行将产生最年轻的行走表现， 证据是：(I)踝关节推力输出的最大增幅和(Ii)代谢能量的最大下降 成本。最终，这项工作将建立一个使用超声成像来指导最佳处方的框架 该辅助装置可有效改善小腿三头肌的踝部肌腱结构 衰老中的运动功能--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.