Medical News Today: Plantar flexion: Function, anatomy, and injuries


Plantar flexion describes the extension of the ankle so that the foot points down and away from the leg.

When in a standing position, this would mean pointing the foot towards the floor.

Plantar flexion has a normal range of motion from about 20 to 50 degrees from the resting position.

In this article, we examine the activities in which plantar flexion may occur, the muscles behind it, and what happens when injuries occur to these muscles.

Function of plantar flexion

Woman walking on tiptoes on wooden beam.
Plantar flexion is a term that describes positioning the foot with the toes furthest down. Standing on tiptoes is an example of plantar flexion.

Many daily activities involve plantar flexion. One typical example is pressing the foot down on the gas pedal in a car.

Standing on the tips of the toes to reach a high shelf is also plantar flexion. Ballet dancers who dance on the tips of their toes (en pointe) have an extreme range of motion in their plantar flexion.

These are more noticeable forms of plantar flexion, but plantar flexion takes place with every step a human takes.

Daily activities that require plantar flexion include:

  • walking
  • running
  • swimming
  • biking
  • dancing
  • jumping

Nearly every sport will require the use of plantar flexion. As a result, athletes are often encouraged to care for their ankles and the surrounding muscles as much as possible.

What controls plantar flexion?

Plantar flexion seems like a simple act, but it requires an entire group of muscles and tendons in the leg and foot.

Most muscles are centered on the tibia (shin bone) and the fibula, which is a thinner bone that supports the tibia. Muscles also attach to the ankle and various bones in the foot.

Gastrocnemius

The gastrocnemius is a muscle that forms half of what is commonly called the calf muscle. It starts at the back of the knee and attaches to the Achilles tendon at the heel.

The gastrocnemius is one of the muscles that does most of the work in plantar flexion.

Soleus

This is a broad and strong muscle that also starts behind the knee and runs beneath the gastrocnemius. It merges into the gastrocnemius to create the Achilles tendon at the heel.

The soleus muscle is responsible for pushing away from the ground. It is vitally important for any movement involving plantar flexion.

Plantaris

The plantaris muscle starts behind the knee, just above the gastrocnemius. The plantaris tendon runs below both the soleus and gastrocnemius muscles to connect directly with the heel bone.

This muscle works with the Achilles tendon to flex both the ankle and knee joints, allowing a person to stand on their toes or point their foot in plantar flexion.

Flexor hallucis longus

This is one of the three deep muscles of the leg. It starts along the back of the fibula and goes through the ankle, running along the sole of the foot to attach to the big toe.

The flexis hallucis longus helps plantar flexion of the ankle, and plays a large role in curling the toes. It is very important for walking and balancing, especially while on tiptoe.

Flexor digitorum longus

This is another deep muscle in the leg. The flexor digitorium longus starts on the back of the tibia near the soleus muscle. The muscle fibers end in a tendon that travels through the ankle and runs along the bottom of the foot.

The flexor digitorium longus attaches to every toe except the big toe. It is this muscle that provides the power to flex the toes themselves. It helps to support the arch of the foot and is used in plantar flexion.

Tibialis posterior

The tibialis posterior is the third deep muscle in the leg. It is the most central leg muscle and is vital in keeping the lower leg stable.

It is attached to interosseous membrane (which separates all bones) in the leg and is connected to the tibia and fibula. The tendon of the tibialis posterior spreads out to attach to the metatarsals, which are the five long bones in the top of the foot. The tibialis posterior is also attached to other bones in the foot – the medial cuneiform, middle and lateral cuneiform, and navicular bones.

Peroneus longus

Peroneus brevis.
The peroneus brevis ensures the foot is stable and any injury may weaken the ability to perform plantar flexion.

The peroneus longus muscle starts at the upper section of the fibula. It runs down most of the fibula bone and attaches to the medial cuneiform and first metatarsal, which are the bones below the large “knuckle” of the big toe.

The tibialis posterior and the peroneus longus work together in the middle foot to create support for the weight-bearing arches of the foot. These two muscles help keep the ankle stable when standing or rising onto the toes.

Peroneus brevis

The peroneus brevis lies just underneath the peroneus longus. It starts in the shaft of the fibula, and the tendon stretches to the foot, where it attaches to the metatarsal of the little toe. The peroneus longus and peroneus brevis help keep the foot stable.

All these muscles and tendons work together in plantar flexion to help the body stay balanced and stable. When there is a problem with even one of these muscles or tendons, the whole system is weakened, causing injury and a reduced range of motion.

Injuries

An injury to any one of the muscles supporting the act of plantar flexion will limit the range of motion of the foot. Ankle injuries are one of the most common ways to severely limit plantar flexion.

The ankle is a very complex joint. It is capable of a wide range of movement to stabilize the body in the most difficult situations, such as hiking or jumping on uneven surfaces. It does this while also protecting key ligaments, arteries, and nerves.

When the ankle is injured, inflammation helps prevent additional injury by reducing the range of motion of the foot. This can drastically reduce plantar flexion, sometimes to the degree where a person cannot move their foot.

Ankle injuries can range in severity from mild sprains to severe fractures. The severity of the injury will determine the treatment.

Treatment

Woman holding an ice compress on her ankle.
Injuries affecting plantar flexion can be treated using ice and compression.

Treating injuries depends on the type of injury that the person has sustained. Mild ankle sprains do not require casts or splints. Instead, they can be treated with rest, ice, compression, and elevation, known as the RICE method.

More severe sprains, tendon injuries, and some fractures will require a splint or cast to hold the ankle in its proper position. During this time, an individual will not be able to put weight on their foot or ankle.

If the ankle is not stable where the fracture has occurred, surgery is usually required. This may mean putting a plate or screws into the bones of the ankle to keep it in position while it heals. It usually takes a minimum of 6 weeks for a fracture to heal.

All forms of ankle, leg, or foot injury that affect plantar flexion will involve physical therapy and exercise to strengthen the muscles and tendons and protect them from future injury. Failing to do these exercises puts people at risk of further injuries in the future.



Preventing injuries

Preventing injuries in the muscles and joints that control plantar flexion starts with doing regular mobility and strength work. There are many exercises that can be done to strengthen the muscles and tendons that are used in plantar flexion and help protect the ankle.

Simple exercises such as toe raises can build strength. Low impact exercise such as swimming and biking can also promote flexibility and strength in the legs, feet, and ankles.

Stepping correctly can also help prevent injuries. Incorrect walking patterns may contribute to injuries over time. This can include walking in high heels or poorly fitted shoes.

Taking conscious steps can help if a person has a tendency to over correct or step incorrectly. It can also help to walk barefoot for at least 30 minutes each day, to allow the feet to walk in their natural position.

An appointment with a podiatrist or orthopedic surgeon may help anyone with regular injuries or limited plantar flexion to find a solution. This may help the doctor understand a person’s walking pattern and decide whether they would benefit from particular shoes or specific exercises.



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