Non-linear properties of the Achilles tendon determine ankle impedance over a broad range of activations in humans.
Non-linear properties of the Achilles tendon determine ankle impedance over a broad range of activations in humans.
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DOI：
10.1242/jeb.244863
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发表时间：
2023-07-01
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调节踝关节力学对于控制与环境的相互作用和拒绝意外干扰至关重要。踝关节力学可以通过阻抗来量化，阻抗是施加的位移和响应产生的扭矩之间的动态关系。踝关节在矢状面的阻抗很大程度上取决于小腿三头肌和跟腱，但他们的相对贡献仍然未知。通常认为踝关节阻抗是通过改变肌肉激活来控制的，从而改变肌肉阻抗，但这忽略了肌腱阻抗也会随着激活诱导的负载而变化。因此，我们试图确定小腿三头肌和跟腱在姿势控制相关条件下的相对贡献。我们使用了一种新的技术，将B型超声成像与关节水平扰动相结合，在最大自主收缩的0%至30%的激活水平上同时量化踝关节，肌肉和肌腱阻抗。我们发现，肌肉和肌腱刚度（阻抗的静态分量）随自主跖屈收缩而增加，但在非常低的载荷（21±7 N）下，肌肉刚度超过肌腱刚度。在这些负荷以上，相当于我们研究中平均参与者最大强度的1.3%，踝关节刚度主要由跟腱刚度决定。在平均参与者约20%MVC时，踝关节刚度对肌腱刚度变化的敏感性是肌肉刚度变化的4倍。我们提供的第一个经验证据表明，神经系统，通过肌肉激活的变化，利用跟腱的非线性特性，增加踝关节僵硬的姿势条件。总结：在姿势条件下，人类踝关节的刚度主要由跟腱的刚度决定，而不是小腿三头肌的刚度。
Regulating ankle mechanics is essential for controlled interactions with the environment and rejecting unexpected disturbances. Ankle mechanics can be quantified by impedance, the dynamic relationship between an imposed displacement and the torque generated in response. Ankle impedance in the sagittal plane depends strongly on the triceps surae and Achilles tendon, but their relative contributions remain unknown. It is commonly assumed that ankle impedance is controlled by changing muscle activation and, thereby, muscle impedance, but this ignores that tendon impedance also changes with activation-induced loading. Thus, we sought to determine the relative contributions from the triceps surae and Achilles tendon during conditions relevant to postural control. We used a novel technique that combines B-mode ultrasound imaging with joint-level perturbations to quantify ankle, muscle and tendon impedance simultaneously across activation levels from 0% to 30% of maximum voluntary contraction. We found that muscle and tendon stiffness, the static component of impedance, increased with voluntary plantarflexion contractions, but that muscle stiffness exceeded tendon stiffness at very low loads (21±7 N). Above these loads, corresponding to 1.3% of maximal strength for an average participant in our study, ankle stiffness was determined predominately by Achilles tendon stiffness. At approximately 20% MVC for an average participant, ankle stiffness was 4 times more sensitive to changes in tendon stiffness than to changes in muscle stiffness. We provide the first empirical evidence demonstrating that the nervous system, through changes in muscle activations, leverages the non-linear properties of the Achilles tendon to increase ankle stiffness during postural conditions. Summary: During postural conditions, the stiffness of the ankle in humans is determined primarily by the stiffness of the Achilles tendon, not that of the triceps surae muscles.
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影响因子：
5.5
作者：
Herbert, RD;Moseley, AM;Gandevia, SC
通讯作者：
Gandevia, SC
DOI：
10.1098/rspb.1938.0050
发表时间：
1938-10-01
期刊：
PROCEEDINGS OF THE ROYAL SOCIETY SERIES B-BIOLOGICAL SCIENCES
影响因子：
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作者：
Hill, AV
通讯作者：
Hill, AV
影响因子：
1.4
作者：
Clark, William H.;Franz, Jason R.
通讯作者：
Franz, Jason R.
影响因子：
2.4
作者：
Epstein, Marcelo;Wong, Max;Herzog, Walter
通讯作者：
Herzog, Walter
影响因子：
4.6
作者：
KIRSCH, RF;BOSKOV, D;RYMER, WZ
通讯作者：
RYMER, WZ