For optimal function and resistance to injury and to better understand exactly what it is you are trying to accomplish with training, it is first important to understand the mechanics of a healthy foot and ankle complex before we begin to discuss dysfunctional patterns and how to approach their management.
At foot-strike the healthy foot contacts the ground on the lateral aspect of the foot in a slightly supinated position with the majority of weight along the fifth ray of the foot and shortly thereafter begins to collapse into pronation. At this time weight is shifted medially across the fifth metatarsal tubercle, to cuboid, to navicular, to cuneiforms 3, 2, 1, then to the metatarsal heads before the foot begins to supinate again. The foot that is ineffective at transitioning between pronation and supination is the foot that will become an issue as a loss of ideal function of the subtalar and ankle mortise joints beget excessive abduction of the foot, changing the line of stress to a more medially oriented one.
As the tibia translates over the foot, the plantar flexors are placed on stretch and reflexively contract after reaching passive insufficiency, loading the Achilles tendon, plantar fascia, and leading to extension of the hallux (and activation of the Windlass Mechanism). To achieve “normal” gait, an athlete must have at minimum, 40 degrees of flexion at the knee, 20-25 dorsiflexion (or more in running, according to Hammer), and at least 65 degrees of extension at the big toe.
Premature contraction of the plantar flexors (due to inadequate length) results in a loss of ability of the subtalar joint to convert energy into rotational energy effectively, and a limitation of hallux extension occurs, often leading to abduction of the foot forcing a medial weigth bearing instead of a plantar surface weight bearing. Additionally, the subtalar and MLA tend to excessively collapse (as a 1 degree abduction leads to 1 degree of dorsiflexion) leading to a group of bigger ramifications up the kinetic chain. Issues may arise including meniscal stress, increased abnormal contact of the femur and acetabulum (Have you heard of labral tearing and impingement, runners?), exaggerated spinal curvatures, and forward head posture (leading to dysfunctional breathing).
Tomorrow we will discuss the Windlass Mechanism further with discussion of mechanics, pathomechanics, and remediation of dysfunction.