The windlass is that equipment which are used by the sailors on yachts to wind the rope around to make it easier to move the sails. In the foot there is a mechanism that is called the windlass mechanism that gets its name from this equipment used on boats. There is a ligament like structure underneath the foot known as the plantar fascia that is at one end attached to the underside of the heel bone and at the other end to the great toe or hallux. When we are walking and the rearfoot comes off the ground, the foot rotates around the great toe where this ligament is connected, tightening up the plantar fascia as it winds about the windlass of the first metatarsal head. This is the windlass mechanism of the foot. It is a crucial function as that ligament is the thing that supports the arch of the foot, therefore it needs to function adequately and efficiently for normal biomechanics. This is the foots natural arch support system.
There are a number of conditions related to this windlass mechanism not functioning adequately. In the event the windlass does not work, then the arch of the foot will collapse from this lack of support and a variety of disorders may develop as a result of that such as bunions and plantar fasciitis. The cause of the windlass not functioning properly can be multiple like the force needed to establish it simply being too high, so the body has to work harder to help make the windlass function. If that effort can make it work, then that is an increased energy expenditure that can be very fatiguing. Clinicians use several design characteristics in foot orthoses to facilitate the windlass mechanism and also to make walking less difficult and more efficient. If the windlass can be established easily when walking won't need so much effort and the foot will naturally support its own arch.