The windlass is that apparatus that 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 known as the windlass mechanism that gets its name from this apparatus used on yachts. There is a ligament like structure under the foot known as the plantar fascia that is at one end attached to the bottom of the heel and at the other end to the big toe. When we are walking and the heel comes of the ground, the foot rotates around the big toe where this ligament is attached, tightening the ligament as it winds around the windlass of the first metatarsal head. This is the windlass mechanism of the foot. It is a vital function as that ligament is what supports the arch of the foot, so it needs to function properly and efficiently for normal biomechanics. It is the foots natural arch support mechanism.
There are a number of conditions associated with this windlass mechanism not working properly. If the windlass does not work, then the arch of the foot will collapse from the lack of support and a range of conditions can develop as a consequence of that such as bunions and plantar fasciitis. The cause of the windlass not working properly can be multiple such as the force needed to establish it just being too high, so the body has to work harder to make the windlass work. If that hard work does make it work, then that is an increased energy expenditure that can be very fatiguing. Clinicians use different design features in foot orthotics to enhance the windlass mechanism and to make walking easier and more efficient. If the windlass can be established easily walking will not require so much energy and the foot can naturally support its own arch.