The Achilles is a long tendon varying in cross-sectional area (CSA) considerably along its length. For the same force, a smaller CSA would experience higher tendon stress and we hypothesised that these areas would therefore undergo larger transverse deformations. A novel magnetic resonance imaging-based approach was implemented to quantify changes in tendon CSA from rest along the length of the Achilles tendon under load conditions corresponding to 10, 20 and 30% of isometric plantar flexor maximum voluntary contraction (MVC). Reductions in tendon CSA occurring during contraction from the resting condition were assumed to be proportional to the longitudinal elongations within those regions (Poisson’s ratio). Rather than tendon regions of smallest cross-sectional area undergoing the greatest deformations, the outcome was region-specific with the proximal (gastrocnemius) tendon portion showing larger transverse deformations upon loading compared to the distal portion of the Achilles (P<0.01). Transverse tendon deformation only occurred in selected regions of the distal Achilles tendon at 20% and 30% of MVC, but in contrast occurred throughout the proximal portion of the Achilles at all contraction levels (10, 20 and 30% of MVC; P<0.01). Calculations showed that force on the proximal tendon portion was ~60% lower, stress ~70% lower, stiffness ~30% lower and Poisson’s ratio 6-fold higher compared to the distal portion of the Achilles tendon. These marked regional differences in mechanical properties may allow the proximal portion to function as a mechanical buffer to protect the stiffer, more highly stressed, distal portion of the Achilles tendon from injury.
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机译:阿喀琉斯是一条长腱,其横截面积(CSA)沿其长度变化很大。对于相同的力,较小的CSA将承受较高的肌腱应力,因此我们假设这些区域将承受较大的横向变形。一种新颖的基于磁共振成像的方法被实施以量化在相应于等距足底屈肌最大自发性收缩(MVC)的10%,20%和30%的负荷条件下沿跟腱长度从静止状态的腱CSA的变化。假定从静止状态收缩期间发生的肌腱CSA减少与这些区域内的纵向伸长率成正比(泊松比)。结节不是区域的最小横截面,而是发生最大的变形,而是区域特定的,近端(腓肠肌)腱部分在负重时显示出比跟腱的远侧部分更大的横向变形(P <0.01)。横向肌腱变形仅发生在跟腱的选定区域,占MVC的20%和30%,但相反,在所有跟腱收缩水平(MVC的10、20和30%,整个跟腱的近端部分均发生); P <0.01 )。计算结果表明,与跟腱的远端相比,近端腱上的力降低了约60%,应力降低了约70%,刚度降低了约30%,泊松比提高了6倍。机械性能上的这些明显的区域差异可允许近端部分充当机械缓冲器,以保护跟腱的较硬,压力更大的远端部分免受伤害。
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