“Cause and effect are two sides of one fact” – Ralph Waldo Emmerson.
During loading and unloading, a functional-healthy foot behaves like a plate lying flat against the ground under the forefoot, and twisting 90° outwards through the midfoot to bisect the heel vertically (MacConaill, 1945). Untwisting and retwisting of the plate confers all of the shock absorbing, stability and lever characteristics of a functional foot during the running cycle. Correct function of the twisted plate depends on a wide, flat and stable forefoot. Dysfunctional low and high arched feet are both caused by a compromised (squashed and unstable) forefoot structure. The excessive twist (high arch) or untwist (low arch) of the rearfoot on the forefoot result from the forefoot instability.
Implications of the over-twisted high-rigid foot in running.
The squashed toes of a shoe-shaped forefoot create an unstable base of support. During forefoot loading in the gait cycle, If muscles are strong enough to overcome the load (250% of bodyweight), supination of the rear foot on the forefoot and external rotation of the hip and can ‘twist and lock’ the foot into a stable position. This excessive twisting of the foot plate creates a high-rigid arch and blocks ankle movement (Manoli and Graham, 2018). The inflexible foot and ankle has poor shock absorption. Stress fractures and lateral ankle sprains are common consequences for runners with this foot type (Williams, McClay and Hamill, 2001). With age and/or increased bodyweight, muscles lose the strength to compensate for the instable forefoot by over twisting the foot plate.
Implications of the untwisted flat-collapsed arch type in running.
The squashed toes of a shoe-shaped forefoot create an unstable base of support. During forefoot loading in the gait cycle, when muscles cannot overcome the load, the rear foot and entire lower kinetic chain collapse inwards and the foot plate is chronically and excessively untwisted. This medial colllapse leads to knee injuries and breaks down soft tissues of the foot resulting in a collapsed-flat arch (Williams, McClay and Hamill, 2001).
The twist of the foot plate and resulting arch height and function are determined by the stability of the forefoot (MacConaill, 1945; Sarrafian, 1987). Forefoot instability, resulting from compromised toe alignment (Stoneham et al., 2020), is the ultimate cause of overly twisted (high-rigid) and overly untwisted (flat-collapsed) arches, and is a causative factor in running injuries associated with these foot types. Forefoot stability results from natural spread of the toes and metatarsals. Footwear must facilitate this. For a functional foot, you must:
Wear functional footwear with freedom for the toes to spread out and lie flat 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.