Ankle joint quasi-stiffness is an aggregate measure of the interaction between triceps surae muscle stiffness and Achilles tendon stiffness. This interaction may be altered due to age-related changes in the structural properties and functional behavior of the Achilles tendon and triceps surae muscles. The authors hypothesized that, due to a more compliant of Achilles’ tendon, older adults would exhibit lower ankle joint quasi-stiffness than young adults during walking and during isolated contractions at matched triceps surae muscle activations. The authors also hypothesized that, independent of age, triceps surae muscle stiffness and ankle joint quasi-stiffness would increase with triceps surae muscle activation. The authors used conventional gait analysis in one experiment and, in another, electromyographic biofeedback and in vivo ultrasound imaging applied during isolated contractions. The authors found no difference in ankle joint quasi-stiffness between young and older adults during walking. Conversely, this study found that (1) young and older adults modulated ankle joint quasi-stiffness via activation-dependent changes in triceps surae muscle length–tension behavior and (2) at matched activation, older adults exhibited lower ankle joint quasi-stiffness than young adults. Despite age-related reductions during isolated contractions, ankle joint quasi-stiffness was maintained in older adults during walking, which may be governed via activation-mediated increases in muscle stiffness.

踝关节准硬度是小腿三头肌硬度和跟腱硬度之间相互作用的综合测量。这种相互作用可能会由于跟腱和小腿三头肌的结构特性和功能行为与年龄相关的变化而改变。作者假设，由于跟腱的顺应性更强，老年人在行走过程中以及匹配小腿三头肌激活的孤立收缩过程中，会表现出比年轻人更低的踝关节准僵硬。作者还假设，与年龄无关，小腿三头肌僵硬和踝关节准僵硬会随着小腿三头肌激活而增加。作者在一项实验中使用了传统的步态分析，而在另一项实验中，则在孤立收缩期间应用了肌电生物反馈和体内超声成像。作者发现年轻人和老年人在行走时踝关节准僵硬没有差异。相反，本研究发现（1）年轻人和老年人通过小腿三头肌长度张力行为的激活依赖性变化来调节踝关节准僵硬，（2）在匹配激活时，老年人表现出比老年人更低的踝关节准僵硬。年轻人。尽管孤立收缩过程中与年龄相关的减少，但老年人在行走过程中仍保持踝关节准僵硬，这可能是通过激活介导的肌肉僵硬增加来控制的。