Effect of the upward curvature of toe springs on walking biomechanics in humans

Freddy Sichting,Oliver B Hansen,Nicholas B Holowka,Daniel E Lieberman

doi:10.1038/s41598-020-71247-9

Abstract

Although most features of modern footwear have been intensively studied, there has been almost no research on the effects of toe springs. This nearly ubiquitous upward curvature of the sole at the front of the shoe elevates the toe box dorsally above the ground and thereby holds the toes in a constantly dorsiflexed position. While it is generally recognized that toe springs facilitate the forefoot’s ability to roll forward at the end of stance, toe springs may also have some effect on natural foot function. This study investigated the effects of toe springs on foot biomechanics in a controlled experiment in which participants walked in specially-designed sandals with varying curvature in the toe region to simulate toe springs ranging from 10 to 40 degrees of curvature. Using inverse dynamics techniques, we found that toe springs alter the joint moments and work at the toes such that greater degrees of toe spring curvature resulted in lower work requirements during walking. Our results help explain why toe springs have been a pervasive feature in shoes for centuries but also suggest that toe springs may contribute to weakening of the foot muscles and possibly to increased susceptibility to common pathological conditions such as plantar fasciitis.

Highlights

That the windlass mechanism has little effect on longitudinal arch motion while the arch is experiencing the high loads associated with push-off
We hypothesized that toe springs would increase the stiffness of the medial longitudinal arch during midstance by engaging the windlass mechanism
MTP joint dorsiflexion at midstance (°) Time of stance phase when COP aligns with MTP joint (°) MTP joint dorsiflexion at moment when COP aligns with MTP joint (°) Peak MTP joint dorsiflexion (°) Total MTP joint range (°) Peak MTP joint velocity Peak MTP joint moment (Nm) Distance of travel of COP distal to MTP joint Negative work (J) Positive Work (J) Midtarsal joint quasi-stiffness at midstance (Nm/°)

Summary

Introduction

That the windlass mechanism has little effect on longitudinal arch motion while the arch is experiencing the high loads associated with push-off. This stiffening effect should be pronounced at midstance, when the foot is loaded by body mass prior to dorsiflexion of the toes at heel lift Following this traditional perspective of the windlass mechanism, a toe spring could passively reduce the need for intrinsic foot muscles to actively resist arch deformation. Another related effect that toe springs could have on the foot concerns energy loss at the MTP joints during the propulsive phase of each step. These effects on foot biomechanics would reduce the total work required of the intrinsic foot muscles, possibly helping to explain their observed atrophy in individuals who habitually wear modern shoes

Methods

Results

Conclusion