School of Sport, Exercise & Rehabilitation Sciences, University of Birmingham, Birmingham, West Midlands, United Kingodm.
PLoS One. 2018 Mar 20;13(3):e0193850. doi: 10.1371/journal.pone.0193850. eCollection 2018.
Individuals may stand with a range of ankle angles. Furthermore, shoes or floor surfaces may elevate or depress their heels. Here we ask how these situations impact ankle stiffness and balance. We performed two studies (each with 10 participants) in which the triceps surae, Achilles tendon and aponeurosis were stretched either passively, by rotating the support surface, or actively by leaning forward. Participants stood freely on footplates which could rotate around the ankle joint axis. Brief, small stiffness-measuring perturbations (<0.7 deg; 140 ms) were applied at intervals of 4-5 s. In study 1, participants stood at selected angles of forward lean. In study 2, normal standing was compared with passive dorsiflexion induced by 15 deg toes-up tilt of the support surface. Smaller perturbations produced higher stiffness estimates, but for all perturbation sizes stiffness increased with active torque or passive stretch. Sway was minimally affected by stretch or lean, suggesting that this did not underlie the alterations in stiffness. In quiet stance, maximum ankle stiffness is limited by the tendon. As tendon strain increases, it becomes stiffer, causing an increase in overall ankle stiffness, which would explain the effects of leaning. However, stiffness also increased considerably with passive stretch, despite a modest torque increase. We discuss possible explanations for this increase.
个体可能处于多种踝关节角度。此外，鞋子或地面可能会抬高或降低脚跟。在这里，我们探讨这些情况如何影响踝关节的刚度和平衡。我们进行了两项研究（每项研究有 10 名参与者），在这些研究中，我们通过旋转支撑表面被动拉伸或通过向前倾斜主动拉伸三头肌、跟腱和腱膜。参与者自由地站在可以围绕踝关节轴旋转的脚踏板上。在 4-5 秒的间隔内施加短暂的、小的刚度测量扰动（<0.7 度；140 毫秒）。在研究 1 中，参与者以选定的前倾角度站立。在研究 2 中，将正常站立与通过将支撑表面倾斜 15 度使脚趾向上引起的被动背屈进行了比较。较小的扰动产生了更高的刚度估计值，但对于所有扰动大小，刚度都随着主动扭矩或被动拉伸而增加。在伸展或倾斜时，摆动受到的影响最小，这表明这不是刚度变化的基础。在安静站立时，最大踝关节刚度受肌腱限制。随着肌腱应变的增加，它变得更硬，导致整个踝关节刚度增加，这可以解释倾斜的影响。然而，尽管扭矩略有增加，但被动拉伸也会导致刚度显著增加。我们讨论了这种增加的可能解释。
