GetBodySmart shows that the tibialis anterior and the tibialis posterior are the two muscles that are the prime movers of inversion of the foot. Both muscles are located along the tibia in the lower leg.
The tibialis anterior and tibialis posterior muscles contract to invert the foot. Inversion of the foot means that the sole of the foot is turned medially, or toward the inside. According to GetBodySmart, the tibialis anterior is located on the front of the lower leg. It originates at the lateral portion of the tibia and inserts at the first cuneiform and first metatarsal of the foot. The tibialis posterior is on the back side of the lower leg. Its origins are the tibia and fibula, and it inserts at multiple bones of the foot.