The windlass is that device that are used by the sailors on yachts to wind the rope around to help to make it easier to move the boom. In the foot there is a mechanism that is known as the windlass mechanism that gets its name from this apparatus used on boats. There is a ligament like structure underneath the foot called the plantar fascia that is at one end connected to the bottom of the heel bone and at the other end to the big toe. When we are walking and the heel bone comes off the floor, the foot rotates around the big toe where this ligament is attached, tensing the ligament as it winds about the windlass of the first metatarsal head. This is the windlass mechanism of the foot. This is a very important functionality as that ligament is what supports the arch of the foot, therefore it needs to function effectively and quickly for normal foot biomechanics. It is the foots own natural arch support system.
There are a variety of conditions related to the windlass mechanism not working adequately. When the windlass mechanism doesn't work, then the arch of the foot will fail from the lack of support and a number of conditions can develop because of that such as bunions and heel pain. The reason for the windlass not working correctly can be multiple like the force necessary to establish it simply being too much, so the body has to work harder to make the windlass function. If that effort does make it work, then that is a greater energy expenditure which can be very fatiguing. Clinicians use different design characteristics in foot orthoses to facilitate the windlass mechanism and to make walking less difficult and more effective. In the event the windlass can be established easily when walking is not going to need very much effort and the foot can naturally support its own arch.