29/12/2025
This image explains how the plantar fascia and rearfoot alignment control shock absorption and push‑off, and what changes in overpronation and oversupination.
Windlass mechanism and plantar fascia
In mid‑stance, the plantar fascia is relatively loose, allowing the small foot joints to move and adapt to the ground so the foot behaves like a mobile shock absorber.
As the toes dorsiflex during push‑off, the plantar fascia tightens (windlass effect), shortening and stiffening the medial arch so the foot becomes a rigid lever that efficiently transmits force for propulsion.
Normal rearfoot mechanics
In normal gait, the heel lands slightly inverted, then pronates just enough so the subtalar joint unlocks and the tibia internally rotates in a controlled way.
From mid‑stance to toe‑off, the foot gradually re‑supinates, the arch rises, and the leg realigns over the calcaneus, giving a straight load line through the heel and lower limb.
Overpronation pattern
In overpronation, the heel and subtalar joint roll too far inward and often stay pronated too long, so the arch stays collapsed and the plantar fascia remains relatively slack.
Because the midfoot never fully “locks,” the foot is too mobile at push‑off, which can overload soft tissues (plantar fascia, tibialis posterior) and drive excessive internal rotation up the tibia and knee.
Oversupination pattern
In oversupination, the heel remains excessively inverted and the subtalar joint does not pronate enough to unlock, so the foot stays rigid throughout stance.
This rigid, high‑arched foot has poor shock absorption; impact forces transmit more directly up the limb, predisposing to stress reactions, lateral ankle sprains, and lateral knee or hip overload.
