Foot biomechanics, which are the movements involved in walking, normally involve the foot acting as a shock absorber and a lever at different points of the walking cycle. The heel hits the ground first, before the foot rolls inward and the arch of the foot flattens to absorb the impact. When the whole of the foot is on the ground the body's weight moves over the foot and forward, while the foot rolls outward and the heel lifts. Normal foot biomechanics then involve the foot acting as a lever, pushing up off the ground from the toes to propel the body forward.
What is known as the gait cycle, or walking cycle, can be divided into two phases, each with differing foot biomechanics. The stance phase describes the part of the gait cycle where the foot is in contact with the ground. That part of the gait cycle where the foot is in the air is known as the swing phase. Usually, the stance phase takes up around 60 percent of the gait cycle, and it can be split into three subphases.
The contact subphase begins when heel contact with the ground occurs. What is called pronation then takes place, where the foot rotates inward at the joint between the ankle bone and the heel bone, known as the subtalar joint. When foot biomechanics are normal, pronating provides a way for the foot to absorb the shock of hitting the ground and to adapt to uneven surfaces, as the arch stretches out and the foot becomes more flexible.
In the midstance subphase, all of the foot touches the ground, bearing the body's weight. Here the foot is still acting as a shock absorber. Next, the weight is transferred forward and what is called supination occurs. During supination, foot biomechanics move the subtalar joint in such a way that the foot rolls outward and the arch rises, forming a lever.
The propulsion subphase is the final part of the stance phase. It begins with lifting the heel, before the lever action of the foot propels the body forward. In what is known as toe off, the toes act as the final part of the mechanism that propels the foot off the ground. Meanwhile the weight of the body moves to the other foot as it strikes the floor. Following toe off, the foot which is in the air enters the swing phase, swinging through the air ready to take the next step, which begins as soon as the heel touches the ground.