Due to the anatomy of the human ankle, when a person's foot hits the ground the resulting forces can be transferred up an individual's whole lower extremity in what are known as "obligatory motions/movements". The shape of the ankle joint forces the tibia (main lower leg bone) to either rotate inwards or outwards depending on the motion that the foot undergoes. The two main movements of the foot that are commonly focused on are "pronation" and "supination".
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