Abstract
The human foot provides numerous functions that let humans deal with various environments. Recently, study of the structure of the human foot and adjustment of an appropriate reaction force and vertical free moment during bipedal locomotion has gained attention. However, little is known about the mechanical (morphological) contribution of the foot structure to the reaction force and free moment. It is difficult to conduct a comparative experiment to investigate the contribution systematically by using conventional methods with human and cadaver foot experiments. This study focuses on the oblique transverse tarsal joint (TTJ) of the human foot, whose mechanical structure can generate appropriate free moments. We conduct comparative experiments with a rigid foot, a non-oblique joint foot (i.e. mimicking only the flexion/extension of the midfoot), and an oblique joint foot. Axial loading and walking experiments were conducted with these feet. The axial loading experiment demonstrated that the oblique foot generated free moment in the direction of internal rotation, as observed in the human foot. The walking experiment showed that the magnitude of the free moment generated with the oblique foot is significantly lower than that with the rigid foot during the stance phase. Using this constructive approach, the present study demonstrated that the oblique axis of the TTJ can mechanically generate free moments. This capacity might affect the transverse motion of bipedal walking.
Highlights
The complex structure of a human foot has numerous important features for dealing with various environments during bipedal royalsocietypublishing.org/journal/rsos R
This study focuses on free moment (FM) generation by the oblique transverse tarsal joint (TTJ) which is called the Chopart joint in clinical research
The axial loading experimental results are shown in figure 10, and the centre of pressure (CoP) positions are listed in table 2
Summary
The complex structure of a human foot has numerous important features for dealing with various environments during bipedal royalsocietypublishing.org/journal/rsos R. The intricate foot structure (i.e. joints, bones, muscles and ligaments) facilitates shock 2 absorption [2], adaptation to uneven terrain, balancing [3] and leverage for propulsion [4]. These functions suggest that the foot structure plays an important role in adjusting the appropriate ground reaction force/moment during bipedal locomotion. The foot structure and its movements are associated with the ground reaction force peaks in different phases of the locomotion [3]. The ground reaction force and vertical free moment generation by the underlying human foot structural deformation needs to be further explored
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