The arch of the human foot is unique among hominins as it is compliant at ground contact but sufficiently stiff to enable push-off. These behaviours are partly facilitated by the ligamentous plantar fascia whose role is central to two mechanisms. The ideal windlass mechanism assumes that the plantar fascia has a nearly constant length to directly couple toe dorsiflexion with a change in arch shape. However, the plantar fascia also stretches and then shortens throughout gait as the arch-spring stores and releases elastic energy. We aimed to understand how the extensible plantar fascia could behave as an ideal windlass when it has been shown to strain throughout gait, potentially compromising the one-to-one coupling between toe arc length and arch length. We measured foot bone motion and plantar fascia elongation using high-speed X-ray during running. We discovered that toe plantarflexion delays plantar fascia stretching at foot strike, which probably modifies the distribution of the load through other arch tissues. Through a pure windlass effect in propulsion, a quasi-isometric plantar fascia's shortening is delayed to later in stance. The plantar fascia then shortens concurrently to the windlass mechanism, likely enhancing arch recoil at push-off.

中文翻译：

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足底筋膜的延展性影响人类跑步过程中的起锚机制

人的足弓在古人类中是独一无二的，因为它在接触地面时是柔顺的，但足够坚硬，可以推开。这些行为部分是由韧带足底筋膜促进的，其作用是两种机制的核心。理想的起锚机机制假设足底筋膜具有几乎恒定的长度，以直接将脚趾背屈与足弓形状的变化结合起来。然而，随着弓形弹簧储存和释放弹性能量，足底筋膜也会在整个步态中拉伸然后缩短。我们的目的是了解当可伸展足底筋膜在整个步态过程中发生应变时，它如何表现得像一个理想的锚机，这可能会损害脚趾弧长和足弓长度之间的一对一耦合。我们在跑步过程中使用高速 X 射线测量了足部骨骼运动和足底筋膜伸长率。我们发现脚趾跖屈会延迟足底筋膜在足部触地时的伸展，这可能会改变通过其他足弓组织的负荷分布。通过推进中的纯锚机效应，准等距足底筋膜的缩短被延迟到站立的后期。然后足底筋膜与锚机机构同时缩短，可能会在推开时增强足弓反冲。