The windlass is that apparatus that are used by the mariners on yachts to wind the rope around in order to make it less difficult to move the sails. In the foot there is a mechanism that is known as 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 which is at one end attached to the bottom of the heel bone and at the other end to the great toe. When we are walking and the rearfoot comes off the floor, the foot rotates around the big toe or hallux where this ligament is connected, tightening the ligament as it winds around the windlass of the first metatarsal bone. This is the windlass mechanism of the foot. This is a vital function as that ligament is what supports the arch of the foot, so it ought to function correctly and efficiently for normal biomechanics. This is the foots natural arch support mechanism.
There are a variety of conditions associated with this windlass mechanism not functioning effectively. In the event the windlass doesn't work, then the arch of the foot will collapse from this lack of support and a range of disorders can develop because of that such as hallux valgus and plantar fasciitis. The explanation for the windlass not working properly can be multiple such as the force needed to establish it simply being too much, so the body needs to work harder to help make the windlass work. If that effort does make it work, then that is a greater energy cost that can be very fatiguing. Clinicians use different design features in foot supports to facilitate the windlass mechanism and to make walking easier and more effective. In the event the windlass can be established easily when walking won't need very much and the foot could naturally support its own arch.