Over Pronation
Over-pronation takes place when the foot/ankle rolls too far inwards thus increasing pressure through the arch of the foot.

Over-pronation is one of the most common causes of foot and leg discomfort. If the arch drops under pressure from over pronation, joint alignment and rotation with be affected, resulting in stressed muscles and soft tissue which then leads to injury.

Poor foot and joint alignment affects the body's ability to absorb shock.

Normal Pronation
Pronation is the movement of the foot/ankle (towards the inside) when a load is applied and isone of the body's primary mechanisms for absorbing shock.

When the correct amount of pronation occurs and the foot and knee work in the correct symmetry there is no negative effect on the body's alignment and posture. However any increase in intensity or endurance can change this, predisposing you to injury.

If pronation increases, the greater the potential for injury.

Supination
Supination is almost dynamically opposed to pronation, it takes place when the foot/ankle rolls towards the outside of the foot, and in doing so the foot becomes rigid (making it a good lever to move you forward).
Supination enables the body to align effectively.

Over supination is rare, yet is the cause of much discomfort for runners and athletes. Over supination locks the foot from pronating and thus nullifying its shock absorbing qualities. These shocks are often transmitted upwards through the lower limbs and into the hip and back.

The lack of shock absorption affects the body's ability to look after itself.