2022-09-27 ペンシルベニア州立大学(PennState)
14人の健康な若者を対象とした研究で、研究者たちは、足指を背屈(つま先が上向きに曲がることで、歩行時にかかとを上げた状態でつま先で地面を押すような動作)させるとアーチの硬さが増すことを発見した。
アーチが硬くなった状態で歩くと、足が地面から離れるときに、より多くのエネルギーが失われることがわかった。
この研究を行ったとき、デイヴィスとチャリスは、足底にある大きな結合組織の束である足底筋膜の役割に主に興味を持ちました。アーチの硬直によって、被験者が歩くときに足の裏でより多くのエネルギーを使うようになるとは思ってもみなかったと言います。
最近のランニングシューズでは、つま先が持ち上がるようにシューズの前部が傾斜しているのが一般的です。これは、足の指と他の部分の関節を永久的に背屈させる可能性があります。しかし、今回の研究では、この関節を背屈させたままのシューズは、足底筋膜に負担をかけ、悪化させる可能性があることが示されました。
<関連情報>
- https://www.psu.edu/news/health-and-human-development/story/new-insights-found-about-how-feet-work-when-people-walk/
- https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0274141
歩行時の足部アーチの硬直:中足趾節関節背屈の寄与を示すin vivoのエビデンス Foot arch rigidity in walking: In vivo evidence for the contribution of metatarsophalangeal joint dorsiflexion
Daniel J. Davis ,John H. Challis
PLOS ONE Published: September 8, 2022
DOI:https://doi.org/10.1371/journal.pone.0274141
Abstract
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.
