Foot arch rigidity in walking: In vivo evidence for the contribution of metatarsophalangeal joint dorsiflexion

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.

Kinetic coupling in distal foot joints during walking

“…The decrease in ROM at the MTP joint induced by our locked brace conditions is comparable to other studies where MTP motion was altered through various mechanisms (e.g. hallux rigidus [12], wedge placed under the toes [13], and sandals with an upward curvature under the toes [14]). All these studies resulted in the MTP joint being more dorsiflexed throughout midstance and having less ROM in late stance compared to controls [12][13][14].…”

Chasing footprints in time – reframing our understanding of human foot function in the context of current evidence and emerging insights

“…However, they found that this increase in stiffness was associated with a considerable reduction in propulsive power (energy return) from the foot. While adding complexity to our understanding of the windlass mechanism, the findings of Davis & Challis (2022) provide further evidence that increasing foot stiffness is not necessarily beneficial for the propulsive function of the foot.…”

“…the inverse of stiffness) as it can deform through a greater range of motion. This implies that a windlass mechanism is unlikely to function to increase the stiffness of the foot during propulsion (Davis & Challis, 2022; Farris et al ., 2019; Sichting & Ebrecht, 2021; Williams et al ., 2022). We highlight that it is very difficult to make assumptions about stiffness in the human foot without direct measurement of the forces/torques involved.…”

“…Their findings were further supported by a motion capture study (Sichting & Ebrecht, 2021) (N = 15), which showed that the windlass mechanism makes the arch more compliant during running compared to sitting and walking. A recent publication (Davis & Challis, 2022) extended Welte's experimental set-up, by wedging the toes in maximum dorsiflexion for the entire walking cycle, to test the relationship between toe extension and arch stiffness. In contrast to Welte et al (2018), they found the arch to be stiffer for the entire stride cycle when the toes were extended.…”

Foot shape is related to load-induced shape deformations, but neither are good predictors of plantar soft tissue stiffness

“…In fact, contrary to the classic understanding of engaging the windlass mechanism to raise the LA and stiffen the foot, Welte et al [20] recently reported that during static loading tasks the windlass mechanism actually makes the arch less stiff, as a higher LA when the windlass is engaged seems to facilitate a greater range of motion for movement. Another recent investigation by Davis & Challis [21] showed that increasing tension in the PA through increased metatarsophalangeal (MTP) joint dorsiflexion does in fact increase LA stiffness during walking, but that foot stiffness can also be increased without increasing PA tension. More importantly, this study also showed that increased LA stiffness may not necessarily favour the energetic efficiency of walking.…”