SUPPORTING EXTERNAL ARCH
The lateral longitudinal and transversal arches form the support triangle, the centre of gravity for which coincides with intersection of triangle’s medians. These two arches are responsible for the stable vertical position of the body and for location of General Centre of Gravity (GCG). If these arches are deformed, it becomes the underlying reason for all other types of deformation (i.e. of feet and vertebral column or spine). Lateral longitudinal arch (external arch) consists of the following bones: heel bone, cubic-shaped bone and two metatarsal bones, and all four of them create the arch-like bone formation, resulting in existence of two joints. These joints provide and secure the arch’s adaptation function (while walking on uneven rugged terrain), and also insure the extinguishing of inertia forces that emerge when movement takes place. The support under arch may be formed and aligned in two possible directions – from heel bone to arch’s apex or from metatarsal head bones to the same apex. The height of arch’s apex (measured in arch’s centre) depends on the muscles condition and on sole’s fascia condition (note that this fascia called plantar aponeurosis is working as bowstring, subtending the heel bone with 4th and 5th metatarsal head bones. When the feet load is minor, the arch amortizes it by stretching the plantar fascia and shin muscles (but the arch’s apex is not projecting itself on the support and is not aligning with it as well). With the increasing of the load the apex is gaining support. In this situation plus the impact of body weight the “roll over” momentum of forces with respect to subtalar joint comes into existence, resulting in turning or pronation of medial longitudinal arch (internal arch).
Thus, the appearance of the support under external arch is the underlying reason for pronation of internal arch. Notice that when regular rigid custom-made orthotics is inserted in close contact under external arch, then immediately internal arch is losing its vital amortizing function. Let’s consider what this loss means and what are its consequences and complications. The fact of the matter is that inertia forces F (imminent and necessary result of walking movement) could reach the magnitude from F = 5mg to F = 20mg (m is body mass and g = 9.8m/sec – acceleration due to gravity). These enormous forces have to be extinguished to the magnitude of F = 0.5mg, particularly to save the brain from shocks. It could be done with the help of one and only one physical agent, namely internal arch and its descending, flattening and springing movements. For this purpose, the larger is the air-gap, the better. But it is obvious that arches in close tight contact with rigid orthotics have no air-gap at all to fulfill this task.
Amortizing ability of external arch is connected with its height as well. When this arch’s muscles are in hypertone, height in its median highest point reaches the value of 5-8mm. While being loaded, external arch does not get into contact with support, hence internal arch is not pronated. Strong muscles contract poorly, therefore blood circulation is deficient. In this condition of muscles overload at daytime, the crumps and twitches often happen at night.