Dominic Stone
Plantar flexion is the extension of the ankle so that the foot points down and away from the leg. This movement is made possible by several muscles in the ankle, leg, and foot, with most muscles centered on the tibia (shin bone) and the fibula. The gastrocnemius, plantaris, soleus, tibialis posterior, flexor digitorum longus, flexor hallucis longus, fibularis longus, and fibularis brevis are all muscles that contribute to plantar flexion. The Achilles tendon is also of vital importance to this movement.
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What You'll Learn
The role of the soleus muscle
The soleus muscle is a powerful muscle located in the back of the lower leg, or the calf. It is one of the muscles responsible for plantar flexion, which is the direction of motion that occurs when the foot and toes point down. The soleus muscle runs from just below the knee to the heel and is involved in standing, walking, running, and jumping. It is closely connected to the gastrocnemius muscle, and some anatomists consider the two muscles to be a single muscle group called the triceps surae.
The soleus muscle is innervated by the tibial nerve, and its blood supply is provided by two main branches: the superior branch, which arises from the popliteal artery, and the inferior branch, which arises from the peroneal artery (also known as the fibular artery) or the posterior tibial artery. The soleus muscle is composed primarily of Type I slow-twitch muscle fibres, which gives it high endurance and the ability to withstand contractions and workloads for prolonged periods.
One of the main roles of the soleus muscle is to plantar flex the foot, working in conjunction with the calf muscle. This means that it helps to push the foot away from the ground and is essential for standing on tiptoes. Additionally, the soleus muscle acts as an extensor and stabiliser of the knee. When the sole of the foot is in firm contact with the ground, activation of the soleus muscle results in closed-chain plantar flexion.
The soleus muscle also has an important function in maintaining proper balance, especially when standing on one foot. It helps to pump blood from the lower leg back to the heart, acting like a sponge to push blood through the veins. An injury to the soleus muscle can affect the ability to perform basic functions such as walking and running, and can result in symptoms such as sharp pain in the calf, swelling, bruising, and weakness.
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The tibialis posterior
Tibialis posterior dysfunction can lead to flat feet and weak arch control in adults. Posterior tibial tendonitis, a condition that involves inflammation or tearing of the posterior tibial tendon, can potentially lead to flatfoot if left untreated.
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The peroneus longus
The main function of the peroneus longus is to produce plantar flexion and eversion of the foot at the ankle joint. When the peroneus longus contracts, it moves the ankle towards the smallest toe and assists the gastrocnemius (calf) muscle in pointing the toes down. This muscle also supports the transverse arch of the foot and helps stabilise the lower leg and ankle during single-leg stance, aiding in balance. The peroneus longus is a strong muscle with high tensile strength, capable of withstanding high forces during activities like walking and running.
The nerve supply to the peroneus longus comes from the lumbar and sacral levels through the superficial peroneal nerve, a branch of the common fibular nerve. The blood supply to the muscle is provided by the anterior tibial and peroneal arteries, with the fibular artery being a branch of the posterior tibial artery. Peroneal tendon injuries commonly occur in young, active individuals, particularly those participating in sports such as soccer, football, and running.
Peroneus longus injuries can result in lateral ankle pain and ankle instability. Tendon subluxation can occur when the peroneus longus tendon moves out of place behind the lateral malleolus of the ankle and then snaps back. This condition may or may not cause pain, but it can lead to extended healing times, sometimes exceeding three months. Peroneal tenosynovitis is another pathological condition affecting the peroneal tendon, characterised by fluid accumulation within the tendon sheath, resulting in swelling and tenderness.
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The plantaris muscle
The function of the plantaris muscle is to act with the gastrocnemius and soleus muscles to flex the knee and plantar flex the ankle. However, its contribution to these movements is considered insignificant. The plantaris muscle contains a high density of muscle spindles, suggesting that it may act as a proprioceptive organ for the larger plantar flexors. Nevertheless, some studies argue that the plantaris muscle may be almost vestigial in humans, as its removal does not seem to affect function.
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The flexor hallucis longus
The FHL is responsible for flexing the great toe, which is essential for maintaining balance and stability when standing on tiptoes or walking. It also plays a role in plantar flexion and foot inversion. This muscle is important for maintaining the medial longitudinal arch of the foot, which helps to absorb shock and provide a stable base for movement.
Injuries to the FHL tendon are common, especially in activities that involve excessive toe flexion such as ballet, gymnastics, and running. FHL tendinitis, also known as "dancer's tendinitis," can cause pain and inflammation at the site of the sustentaculum tali, a bony landmark in the ankle. Other common injuries associated with the FHL tendon include tenosynovitis, tendinopathies, and muscle strains. These injuries can be diagnosed using an MRI or diagnostic ultrasound, and treatment options range from conservative management to surgery, depending on the severity of the injury.
Rehabilitation exercises for the FHL may include walking or running on different surfaces, such as grass or sand, to challenge the muscle and improve its function. Stretches can also be performed by pulling the great toe into an extended position while dorsiflexing the ankle.
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Frequently asked questions
Plantar flexion is the extension of the ankle so that the foot points down and away from the leg. This movement is made possible by several muscles in the leg and foot.
The main muscles involved in plantar flexion are the gastrocnemius, plantaris, soleus, tibialis posterior, flexor digitorum longus, flexor hallucis longus, fibularis longus, and fibularis brevis.
An injury to any of the muscles that support plantar flexion can limit your ability to flex your foot or stand on tiptoe. It is important to strengthen the muscles in your ankle, leg, and foot that support plantar flexion to keep your foot flexible, protect your ankle, and prevent future injuries.
