During normal gait, the foot supinates (rolls outwards) a bit on heel strike, then pronates a bit when your midfoot hits the ground. This normal supination and pronation are the foot’s functions to handle shock (Ground Reaction Force or GRF) that is generated due to impact of the foot with the ground. When the foot rolls outwards excessively, it is called over supination. In such a case, the foot is not able to pronate sufficiently after the heel strike and the majority of the body weight continues to be handled by the outer (lateral) side of the foot. In cases of severe supination, the lateral weight bearing causes the individual to move ahead with the brunt of the propulsion being borne by the third, fourth and fifth toes instead of the first and second toes that act as the main propellors during normal gait. 

Like over pronation, over supination of the foot causes misalignment in the lower limb and can cause hip and back pain, ankle injuries, plantar fasciitis and excessive stress on the lateral side of the knee. People whose feet supinate too much are likely to experience ankle pain, ankle sprains, corns and calluses on the outer edge of the foot. They can also experience knee pain due to ITB Syndrome. 

The optimum solution for over supination is a pair of well designed custom insoles that are fabricated after an analysis to determine the nature and extent of the supination and its effects on the patient.