The lower leg consists of two long bones and four muscular compartments; the anterior, the lateral, superficial posterior, and deep posterior, each of which contains several muscles making it quite compact. The primary function of these muscles is to control the active and passive movement of energy through the foot and toes via the ankle joint. The secondary function of these muscles are in back of the leg, called the posterior muscles. They control the knee during various phases of athletic activity and play a role in flexing. The third and final purpose of the muscles is to provide the fine balance of contractions and relaxations that allow an individual to stand for a significant amount of time.
The tibia, or shin bone, runs along the front of the lower leg. Because it’s close to the surface of the skin, the tibia can easily be damaged by blunt force and not necessarily a particularly hard one. Shin guards are, therefore, essential gear for sports such as soccer and martial arts where there’s a likelihood of contact to that area. The tibia flares out at each of its ends. At the top, or proximal end, it forms the knee joint and serves as a support column for the massive femur and a person’s bodyweight. Below, at the distal end, it has a cup-like cavity that sits like a lampshade above the talus, forming the ankle joint. This mortise-like structure has a lip on the medial side, the side of the big toe, that extends farther downward to form the medial malleolus. The lower portion of the tibial shaft, just above the mortise, is the thinnest part of the bone, and is therefore is the part most vulnerable to injury and fractures.
The fibula is even thinner than the tibia, it’s main purpose is to support the complex of muscles in the lower leg. Like the tibia, the fibula also extends to the ankle and contributes to 60% of the stability of the joint. It has a lip that extends downward, forming the lateral malleolus of the ankle, which is tied to the side of the talus with ligaments. The lateral malleolus is about 1/2 an inch lower than the medial malleolus, which is one reason why inversion, or inward-turning, sprains are more common than eversion, or outward-turning, sprains.
Peroneus longus and peroneus brevis are the muscles which run down the outer part of the leg. They raise the outer border of the foot and dorsiflex the ankle. They also provide protection against inversion sprains of the ankle by preventing the foot from turning inward.
The gastrocnemius is the calf muscle closest to the surface of the skin and extends from above the knee to the calcaneus. It assists the hamstrings in flexion of the knee, in addition to plantar flexing the foot. The soleus is a calf muscle deeper than the gastrocnemius, it assists the gastrocnemius with plantar flexion and is important in stabilizing the tibia during movement like walking and running.
The Achilles tendon is a single, powerful cord of tissue that connects the heel of the foot to the muscles of the calf, the gastrocnemius and soleus. These calf muscles drop down toward the heel and work through the Achilles tendon, they are the main source of power in plantar flexing the foot for sprinting, running, pedaling and jumping.
The posterior and anterior tibialis muscles are located in close proximity to the tibia. The posterior tibialis aids in plantar flexion, turning the foot inward and helping to support the arch. The anterior tibialis dorsiflexes the foot so that it clears the ground when the leg is swung forward during movement like running or walking. When the foot initially contacts the ground, the tibialis anterior is responsible for slowly lowering the foot to the ground in a controlled manner.
The flexors and extensors are small muscles that control the movements of the toes. The flexor digitorum curls the four small toes, while the flexor hallucis pushes the big toe, or the hallux, downward. The extensor digitorum originates along the tibia, it moves down along the top of your foot, and connects to the four small toes, where it pulls them upward. The extensor hallucis runs parallel to the extensor digitorum and pulls the big toe upward. Common lower leg problems include shin splints, calf strains, peroneal tendinitis and Achilles tendonitis. These problems can become recurrent and chronic, so it’s vital to know when to back off of exercise and allow adequate time to heal.
High arches or a chronically sprained ankle, the peroneals longus and brevis, requires more work to stabilize the foot, this can lead to potential inflammation. The pain is felt along the lateral side of the lower leg or ankle. Peroneal tendinitis can also result from an ankle sprain that damages the retinaculum, a band of fibrous tissue designed to hold the end of the peroneal tendon in place in a groove behind the lateral malleolus. Among skiers and skaters, the peroneal muscle can also become strained by a forward fall. A chronically weak or inflamed peroneal tendon increases the likelihood of recurrent ankle sprains. Peroneal tendinitis should be treated like any other soft tissue inflammation. Maintain a regiment of cold therapy, compression and rest to facilitate and expedite recovery. If the retinaculum is damaged as a result of an ankle sprain it may need surgical repaired.
The Achilles tendon is the lowermost channel for most of the impact that occurs when the foot makes contact with the ground. It bears a tremendous load during normal activity, but during sports it’s frequently taxed beyond its limits. When the overload continues unabated, particularly past age 30, tendons start losing their resiliency, the result is small tears in the tendon fibers, which create a syndrome of chronic debilitating pain and weakness. Runners, particularly hill runners and distance runners, as well as cyclists, hard riders who grind long distances in high gear, are among athletes most susceptible to these types of injuries. Increasing mileage, wearing different shoes, running on hard surfaces or coming back too aggressively after a long period of inactivity increases the likelihood of Achilles tendonitis.