Injury Prevention: Biomachanics & Gait Cycles
The Kinetic Chain
The body is a kinetic chain of interconnected parts. The feet and ankles form the foundation of this chain. Just as a building needs a good foundation, so your body needs healthy balanced feet and ankles. Imbalances or malpositions in feet and ankles requires the knees, hips, and back to compensate, negatively affecting the rest of the kinetic chain. This can lead to discomfort and injury.
Pronation and Supination
There are two biomachnical actions of the foot that occur during the gait cycle that are critical to understand when buying shoes and / or insoles.
Pronation is to rotate the medial bones in the midtarsal region of the foot inward and downward so that the inner edge of the sole bears the body's weight. This is the body's natural way of absorbing shock and adapting to uneven surfaces.
6 - 9 mm of pronation (an angle of 6 -10 degrees) is considered normal. This provides proper shock absorption for the stress of standing, walking, running and jumping.
Pronation above this amount is considered excessive (Overpronation). Overpronation exposes the body to injuries throughout the kinetic chain.
Supination is to turn or rotate the foot outward so that the outer edge of the sole bears the body's weight. Supination can be thought of as the opposite of pronation. When it occurs at appropriate moments in the gait cycle, supination is the body's natural way to convert the foot into a rigid lever for propulsion. However, supination can be harmful when it occurs instead of pronation or at the wrong moments in the gait cycle.
Normal Pronation / Neutral Gait
In this gait type the outside of the heel strikes the ground first. The foot rolls inward slightly to efficiently absorb shock and allow the foot and ankle to properly support the body. The foot pushes off evenly at the end of the gait cycle with appropriate pronation. Ankles and feet maintain the vertical line of the lower leg.
In this gait type the foot rolls inward excessively, preventing the foot and ankle from properly stabilising the body. Shock is not efficiently absorbed and efficiency is reduced.