The 20 muscles in your feet work with the joints to help you move in a variety of ways. They include dorsiflexion, moving the foot upward, and plantar flexion, pointing the foot downward; abduction, turning the toes out, and adduction, turning the toes in; inversion, directing your inner foot upward, and eversion, directing the outer foot upward.
Intrinsic and Extrinsic
The feet have two types of muscles: extrinsic and intrinsic. The extrinsic muscles originate from the three bones in the leg---the femur, tibia and fibula---and then insert to bones of the foot. The intrinsic muscles, located only within the foot, help move the toes and support the arches.
Extrinsic Anterior Muscles
The four extrinsic muscles that run along the front of the leg to the top of the foot are the tibialis anterior, extensor hallucis longus, extensor digitorum longus and peroneus tertius. These help the foot with dorsiflexion and stepping forward in walking. THe peroneus tertius inserts into the small toe to help with dorsiflexion and eversion.
Extrinsic Lateral Muscles
The extrinsic lateral muscles, which run along the outer part of the leg, include the peroneus longus and peroneus brevis. The peroneus longus ends at the base of the big toe, while the peroneus brevis ends at the base of the small toe. These two muscles cross under the middle of the foot to create a "sling." This sling supports the arches, stabilizes the ankle and helps maintain balance.
Extrinsic Posterior Muscles
The five muscles that run along the back of the leg to the bottom of the foot are the flexor digitorum longus, tibialis posterior, flexor hallucis longus, gastrocnemius and soleus. The flexor digitorum longus, tibialis posterior (which is also part of the foot's sling) and flexor hallucis longus help the feet in plantar flexion, inversion and arch support. The gastrocnemius and soleus, the calf muscles, serve as the ankle's plantar flexors.
Intrinsic Muscles
The extensor digitorum brevis runs from below the outer ankle to all but the baby toe and works with the extensor digitorum longus to help dorsiflexion. The rest of the intrinsic muscles come in four layers. The deepest layer, the interossei, of which there are seven (four dorsal and three plantar), helps with walking and spreading the toes.
The flexor hallucis brevis in the third layer helps plantar flexion of the big toe. The adductor hallucis adducts the big toe, and the flexor digiti minimi brevis helps the little toe's plantar flexion.
The quadratus plantae (or flexor digitorum accessorius), in the second layer, works with the flexor digitorum longus. Also in the second layer, the lumbricals help push the toes off the ground for walking.
In the first layer, the flexor digitorum brevis helps plantar flexion of the four smaller toes. The abductor hallucis plantar flexes and abducts the big toe and keeps it aligned while you're walking. The abductor digiti minimi abducts the little toe and supports the lateral arch.
References
- Bartelby.org: The Muscles and Fascia of the Foot
- Anatomy of Movement; Blandine Calais-Germain; 1993
- Podiatry Channel: Anatomy of the Foot and Ankle
