02/02/2026
The foot and ankle are not passive structures at the end of the leg—they are powerful biomechanical engines that drive forward movement. During walking and running, the ankle-foot complex functions like a spring–lever system, converting stored elastic energy into propulsion. What looks like a simple push-off is actually the result of precise coordination between bones, ligaments, muscles, and tendons.
As the body progresses over the foot in late stance, the ankle moves into dorsiflexion while the heel lifts. This motion stretches the Achilles tendon and the plantar soft tissues, especially the plantar fascia. At the same time, the forefoot becomes the primary contact with the ground, increasing load through the metatarsal heads. This loading phase is critical because it allows elastic energy to be stored rather than wasted as muscular effort.
The moment the heel rises further, the windlass mechanism is activated. Dorsiflexion of the big toe tightens the plantar fascia, raising the medial longitudinal arch and transforming the foot from a flexible shock absorber into a rigid lever. This stiffening of the foot allows force generated by the calf muscles to be efficiently transmitted into the ground instead of being lost through midfoot collapse.
The gastrocnemius–soleus complex then contracts powerfully, releasing the stored elastic energy in the Achilles tendon. This recoil contributes significantly to forward propulsion, reducing the metabolic cost of movement. In running, this spring-like behavior becomes even more pronounced, allowing the ankle to behave like a loaded coil that snaps back during toe-off.
When this system is disrupted—due to reduced ankle mobility, weak calf musculature, poor arch control, or altered foot posture—the mechanics change dramatically. A collapsed arch or limited big toe extension delays or weakens the windlass effect, forcing the calf muscles to work harder and increasing stress on the Achilles tendon, plantar fascia, and forefoot. Over time, this inefficiency can contribute to conditions such as plantar fasciitis, Achilles tendinopathy, or forefoot pain.
In essence, effective propulsion depends on a delicate balance: the foot must be flexible enough to absorb load early in stance, yet stiff enough to act as a lever at push-off. Training, rehabilitation, and gait retraining should respect this dual role of the foot–ankle complex. When the ankle and foot work as a coordinated spring–lever system, movement becomes smoother, faster, and far more energy-efficient.
