“If a theory disagrees with experiment, it is wrong … in that simple statement is the key to science” Richard Feynman – Nobel Prize winning Physicist.
The previous post outlined the ‘tripod’ model of foot function, shown incorrect by experimental observations, yet still commonly applied, and how application of that model brands functional feet as dysfunctional and prescribes arch supports that exacerbate dysfunction in high-arched, inflexible feet. A model of foot function that agrees with experimental data and leads to correct solutions to common foot problems is the ‘twisted plate’ model.
The twisted plate model was proposed by MacConaill (1945). In a series of experiments using footprints and radiography, MacConaill demonstrated that the bones and ligaments of the foot form a twisted plate, flat against the ground under the toes and metatarsal heads and twisting through the mid foot to vertically bisect the heel bone. The twisting and untwisting of the plate accounts for the observed rotation of the forefoot relative to the heel and vice versa, as well as the observed flattening and raising of the medial and lateral longitudinal arches during the loading and unloading of a gait cycle.
The twisted plate explains all aspects of normal foot function i.e. how the foot acts as a flexible entity to conform to the ground and absorb shock in early stance, before becoming a stable and rigid lever for propulsion in late stance, and agrees with footprints, pressure and other biomechanical data from healthy-functional feet. The twisted plate also accounts for data from dysfunctional feet where the foot plate is overly twisted (high-arched, rigid feet) and overly untwisted (collapsed feet).
A crucial element of the twisted plate model is the horizontal stability of the forefoot against the ground prior to full loading of the foot, such that foot plate is anchored at one end, and pronation then supination of the rearfoot relative to the stable forefoot can act to untwist then re-twist the foot plate conferring shock absorbing then rigid lever properties as weight moves onto then off the supporting foot. Without a stable forefoot segment, the plate cannot function and the foot is either locked in an overly twisted position to create the missing stability (high-arched, rigid foot) or else the plate collapses and the entire foot pronates inwards (collapsed arch).
The twisted plate model dictates that a functional foot requires a stable forefoot. Forefoot stability is created by a natural spread of the toes and metatarsals. Footwear must facilitate this. In other words, for a functional foot, you must wear functional footwear with freedom for the toes to spread out and lie horizontal to the ground. Only then can the foot plate untwist and re-twist as nature intended conferring the stability, shock absorption and leverage of a functional foot.