A ‘windlass’ refers to a centuries-old mechanism used for shifting heavy objects.
The windlass apparatus is a lifting or pulling device consisting of a rope or belt winding around a horizontally placed drum that rotates by motor or by turning a crank.
According to John Hicks (from 1954), the bones and ligaments of the foot are arranged in a triangular arch structure. Starting posteriorly, the calcaneus (heel bone), the midtarsal joint (top of foot) and then the first metatarso-phalangeal joint (big toe joint) form the triangular arch. The plantar fascia stretches from the calcaneus (heel bone) to the proximal phalanges of the toes forms the base of this triangle. As the toes (especially the big toe) are lifted, you pull on/wind up the plantar fascia, this shortens the distance between toes and heel, elevating the foot arch (medial longitudinal arch) and this is the essence of the Windlass Mechanism.
The foot serves several important functions. It enables propulsion through space, adaptation to uneven terrain, absorption of shock, and support of body weight. Terrain adaptability is necessary to walk or run on uneven surfaces.
The foot forms a rigid lever arm that gives us the ability to push off, primarily from the big toe. Vertical forces from body weight travel downward and tend to flatten the medial longitudinal arch, while the ground reaction forces travel upward, which can further this flattening effect.
The Windlass Mechanism in Action:
As the foot touches the ground, the toes are flexed, and the arch is high (fully winded up). This position is ideal for absorbing the shock of the whole body’s weight.
When on the ground, the toes straighten out, relaxing the plantar fascia. The arch of the foot flattens under the vertical load of the body, thus dispersing the weight in a controlled fashion.
Further flattening of the arch is restricted by the plantar fascia, which, secondary to its tensile strength, maintains a certain amount of foot arch, even during a weight bearing position.
During propulsion (as we push off our toes), the heel is lifted upwards, which bends the toes. The bending of the toes leads to a winding of the plantar fascia around the metatarsal heads at the base of the big toe. The fascia is tightened, lifting the heel further upwards and compressing all the joints in the foot. This transforms the foot from a loosely packed bag of bones to a rigid lever, to propel the body from.
During a gait cycle (how we walk), many forces stress the foot and can disrupt the foot arch. Without a mechanism to maintain this arch, we could not walk in a systematic and efficient manner, absorbing body weight, shocks and uneven terrain.
The orientation of the plantar fascia helps maintain the arch throughout gait and contributes significantly to the appropriate amount and timing of pronation and supination during the gait cycle.
Looking at the windlass mechanism and its biomechanical link we can understand why an abnormal gait cycle, ‘lazy’ stride or an altered foot position during gait, will have a negative impact on the rest of the body, potentially resulting in injuries and/or put stress on other joints, muscles and ligaments!