15.20: Muscles of the Leg that Move the Foot and Toes
The human leg comprises an intricate system of muscles that facilitate the movement of feet and toes. Within this system, the muscles are categorized into the anterior, lateral, and posterior compartments, each with a unique set of muscles carrying out specific functions.
Anterior Compartment
The anterior compartment includes muscles that contribute to the dorsiflexion of the foot. This compartment houses the tibialis anterior, extensor hallucis longus, and extensor digitorum longus muscles. The tibialis anterior muscle, situated along the tibia's lateral surface, is easily felt and is the thickest. The tibialis anterior also causes foot inversion. Additionally, the extensor hallucis longus and extensor digitorum longus extend the great toe and other toes, respectively. The fibularis tertius muscle, originating from the same source as the extensor digitorum longus, is also present here. It everts the foot.
Shin splints, medically referred to as medial tibial stress syndrome, are a common affliction among athletes, especially runners and dancers. It results from overuse and repetitive stress of the anterior compartment muscles. Preventive measures include regular stretching, strength training, and choosing appropriate footwear.
Lateral Compartment
The lateral compartment contains the fibularis longus and fibularis brevis muscles. The fibularis longus is the longer and more superficial of the two muscles. It originates from the head and upper portion of the fibula, the outer and thinner of the two bones in the lower leg, and the adjacent intermuscular septa. The fibularis brevis, lying just beneath the fibularis longus, is shorter and originates from the lower two-thirds of the fibula. These two muscles help in the plantar flexion and eversion of the foot.
Posterior Compartment
The posterior compartment is further divided into superficial and deep muscle groups. The superficial group includes the gastrocnemius, soleus, and plantaris muscles, commonly called the calf muscles. These muscles share the Achilles tendon, the body's most robust tendon, which attaches to the calcaneal bone of the ankle. The human upright stance is attributed to the size of these muscles. The gastrocnemius forms the calf's prominent part, while the soleus, found beneath the gastrocnemius, bears a flat, broad look. The plantaris, a small muscle, is nestled between these two muscles and is absent in some individuals.
The deep posterior compartment houses the popliteus, tibialis posterior, flexor digitorum longus, and flexor hallucis longus muscles. The popliteus forms the floor of the popliteal fossa. The tibialis posterior is the deepest muscle in the posterior compartment, positioned between the flexor digitorum longus and flexor hallucis longus muscles. Despite flexing just the big toe at the interphalangeal joint, the flexor hallucis longus is larger than the flexor digitorum longus, which flexes the other four toes.
