The Biomechanics Laboratory, The Pennsylvania State University, University Park, PA, United States of America.
PLoS One. 2022 Sep 8;17(9):e0274141. doi: 10.1371/journal.pone.0274141. eCollection 2022.
Human foot rigidity is thought to provide a more effective lever with which to push against the ground. Tension of the plantar aponeurosis (PA) with increased metatarsophalangeal (MTP) joint dorsiflexion (i.e., the windlass mechanism) has been credited with providing some of this rigidity. However, there is growing debate on whether MTP joint dorsiflexion indeed increases arch rigidity. Further, the arch can be made more rigid independent of additional MTP joint dorsiflexion (e.g., when walking with added mass). The purpose of the present study was therefore to compare the influence of increased MTP joint dorsiflexion with the influence of added mass on the quasi-stiffness of the midtarsal joint in walking. Participants walked with a rounded wedge under their toes to increase MTP joint dorsiflexion in the toe-wedge condition, and wore a weighted vest with 15% of their body mass in the added mass condition. Plantar aponeurosis behavior, foot joint energetics, and midtarsal joint quasi-stiffness were compared between conditions to analyze the mechanisms and effects of arch rigidity differences. Midtarsal joint quasi-stiffness was increased in the toe-wedge and added mass conditions compared with the control condition (both p < 0.001). In the toe-wedge condition, the time-series profiles of MTP joint dorsiflexion and PA strain and force were increased throughout mid-stance (p < 0.001). When walking with added mass, the time-series profile of force in the PA did not increase compared with the control condition although quasi-stiffness did, supporting previous evidence that the rigidity of the foot can be actively modulated. Finally, more mechanical power was absorbed (p = 0.006) and negative work was performed (p < 0.001) by structures distal to the rearfoot in the toe-wedge condition, a condition which displayed increased midtarsal joint quasi-stiffness. This indicates that a more rigid foot may not necessarily transfer power to the ground more efficiently.
人类足部刚性被认为可以提供更有效的杠杆，从而更有效地推地。随着跖趾关节（MTP）背屈的增加，足底筋膜（PA）的张力（即辘轳机制）被认为提供了部分刚性。然而，关于 MTP 关节背屈是否确实增加足弓刚性存在越来越多的争议。此外，即使 MTP 关节背屈增加，足弓也可以变得更刚性（例如，当行走时增加质量）。因此，本研究的目的是比较增加 MTP 关节背屈和增加质量对行走中中跗关节准刚性的影响。参与者在脚趾下垫一个圆形楔形物以增加脚趾楔形物条件下的 MTP 关节背屈，在添加质量条件下穿着带有其体重 15%的负重背心。在条件之间比较足底筋膜行为、足部关节能量学和中跗关节准刚性，以分析足弓刚性差异的机制和影响。与对照条件相比，脚趾楔形物和添加质量条件下的中跗关节准刚性增加（均 p < 0.001）。在脚趾楔形物条件下，MTP 关节背屈和 PA 应变和力的时间序列曲线在整个中间阶段都增加（p < 0.001）。当行走时增加质量，PA 中的力的时间序列曲线与对照条件相比没有增加，尽管准刚性增加，这支持了先前的证据，即足部的刚性可以主动调节。最后，在脚趾楔形物条件下，距后足更远的结构吸收更多的机械功率（p = 0.006）并进行负功（p < 0.001），这是一种显示中跗关节准刚性增加的条件。这表明更刚性的足部不一定能更有效地将力量传递到地面。
