Ebrahimi Anahid, Martin Jack A, Schmitz Dylan G, Thelen Darryl G
Department of Mechanical Engineering, University of Wisconsin-Madison, Madison, WI, United States.
Department of Orthopedics and Rehabilitation, University of Wisconsin-Madison, Madison, WI, United States.
Front Sports Act Living. 2020 Jun 19;2:69. doi: 10.3389/fspor.2020.00069. eCollection 2020.
Prior studies have observed an age-related decline in net ankle power and work at faster walking speeds. However, the underlying changes in muscle-tendon behavior are not well-understood, and are challenging to infer from joint level analyses. This study used shear wave tensiometry to investigate the modulation of force and work done by the triceps surae across walking speeds. Fourteen healthy young (7F/7M, 26 ± 5 years) and older (7F/7M, 67 ± 5 years) adults were tested. Subjects walked on an instrumented treadmill at four walking speeds (0.75, 1.00, 1.25, and 1.50 m/s) while lower extremity kinematics and Achilles tendon shear wave speeds were collected. Subject-specific calibrations were used to compute Achilles tendon force from wave speed. Excursions of the soleus and gastrocnemius muscle-tendon units were computed from the kinematic data and subject-specific measures of the Achilles tendon moment arm. Work loop plots were then used to assess effective muscle-tendon stiffness during lengthening, and positive, negative, and net work production during stance. Two-way mixed ANOVAs were used to evaluate the effects of age group and walking speed on each outcome measure. Tendon loading during muscle-tendon lengthening (effective stiffness) did not differ between age groups, but did vary with speed. The soleus became effectively stiffer with increasing speed while the gastrocnemius became effectively more compliant. There was a marked age-related deficit in net soleus (-66% on average) and gastrocnemius (-36%) work across all walking speeds. We did not observe an age-speed interaction effect on net work production. These results suggest the age-related deficit in triceps surae output in walking is pervasive across speed, and hence seemingly not linked to absolute mechanical demands of the task.
先前的研究观察到，在较快步行速度下，踝关节净功率和功随年龄增长而下降。然而，肌肉-肌腱行为的潜在变化尚未得到充分理解，并且从关节水平分析中难以推断。本研究使用剪切波张力测定法来研究在不同步行速度下腓肠肌三头肌所做的力和功的调节情况。对14名健康的年轻人（7名女性/7名男性，26±5岁）和老年人（7名女性/7名男性，67±5岁）进行了测试。受试者在装有仪器的跑步机上以四种步行速度（0.75、1.00、1.25和1.50米/秒）行走，同时收集下肢运动学和跟腱剪切波速度数据。使用个体特异性校准从波速计算跟腱力。根据运动学数据和跟腱力臂的个体特异性测量值计算比目鱼肌和腓肠肌肌肉-肌腱单元的位移。然后使用功环图来评估肌肉-肌腱在拉长过程中的有效刚度，以及站立期间的正向、负向和净功产生情况。使用双向混合方差分析来评估年龄组和步行速度对每个结果测量指标的影响。年龄组之间在肌肉-肌腱拉长过程中的肌腱负荷（有效刚度）没有差异，但随速度而变化。随着速度增加，比目鱼肌的有效刚度增加，而腓肠肌变得更易顺应。在所有步行速度下，比目鱼肌（平均-66%）和腓肠肌（-36%）的净功存在明显的年龄相关缺陷。我们没有观察到年龄-速度交互作用对净功产生的影响。这些结果表明，在步行中，腓肠肌三头肌输出的年龄相关缺陷在不同速度下普遍存在，因此似乎与任务的绝对机械需求无关。
