The ability to dorsiflex the toes relative to the rest of the foot at the metatarsophalangeal (MTP) joints during the propulsive phase is one of the key evolved features that enable humans to walk and run bipedally effectively and efficiently. (A) Dorsiflexion at the MTP joints helps stiffen the foot through a windlass mechanism. During this action, dorsiflexion of the toes creates tension in the plantar aponeurosis that tends to pull the calcaneus towards the metatarsal heads. This motion creates an upward force in the longitudinal arch. (B) During propulsive phase, the metatarsal heads and the distal phalanges are the only points of contact with the ground on the trailing leg and hence become load-bearing. As a result, the ground reaction force (vGRF) acts on the distal phalanges at a distance R from the MTP joint center to generate a moment that causes the MTP joints to dorsiflex. (C) The intrinsic flexor muscles are active (Fflex) at the end of stance phase, balancing the dorsiflexion moments at the MTP joints (with r as the lever arm of the acting flexor muscles).