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Spotlight on the Soleus

Remember the soleus muscle from our previous blog post?

Remember that alongside the gastrocnemius and the plantaris muscles, it forms part of the calf muscle group of muscles?

Remember what a crucial part it plays in assisting the heart with blood circulation?

Well, that’s not the only reason for keeping it strong and healthy. We use the calf muscle a lot - when we stand, walk, run and jump! A strong gastrocnemius is important, but a strong soleus muscle is an important tool too in prevention and rehabilitation of lower leg injuries such as plantar fasciitis and Achilles tendinopathy. It's also a vital tool in helping to prevent mobility issues generally, particularly as we age.

Firstly, let’s look at the anatomical difference between the soleus and the gastrocnemius muscle (the one that is easily visible on top).

Whilst both extend from the knee to the ankle, joining together to form the Achilles tendon, there are distinct differences in where these two muscles attach at the back of the knee. Whilst the two-headed, bulky, gastrocnemius attaches above the knee joint at the lower end of the femur (thigh bone), the large, flat soleus attaches beneath the knee joint at the top of the fibula bone, one of the two bones that make up the shin bone. These two muscles are therefore set up to do different things and so we need to approach them differently.

Soleus Muscle

Gastrocnemius Muscle

So what's the gastrocnemius set up to do?

The gastrocnemius (gastroc for short) is involved in plantarflexion of the ankle (enabling you to point your foot downwards and to stand on your toes) and flexion (bending) of the knee. It has a high density of fast-twitch muscle fibres (type 2) which are vital for producing force and dynamism, particularly important for sprinters and tennis players for example. However, because of this and because it crosses two joints (the knee and the ankle), it is more prone to fatigue and at a much higher risk of injury.

Ok, so what's the soleus set up to do?

Like the gastroc, the soleus is involved in plantarflexion of the ankle but it is not involved in flexion (bending) of the knee. However, depending on how bent the knee is, determines which of the two becomes the primary muscle involved in plantarflexion of the ankle. The more bent the knee, the more the soleus is the primary force in that movement. Conversely, the straighter the knee, the more the gastroc becomes the primary player. The soleus consists mostly of slow-twitch muscle fibres (type 1) which are important for endurance, from maintaining your posture, to walking, jogging and long-distance running. As a result of this, and because it only crosses one joint (the ankle), it is less prone to injury and fatigue.

A quick note about the third muscle in the calf muscle (triceps surae) group. What does the plantaris do?

Plantaris Muscle (Side View)

Plantaris Muscle (Back View)

The plantaris is largely functionless as a result of human evolution and today acts only as a weak plantar flexor of the ankle and flexor of the knee. It is thought to be what remains of a larger plantar flexor of the foot. The plantaris of reptiles, which serves as an important muscle of propulsion, still retains a lot of the basic character of this older, larger flexor in humans. It is now so underdeveloped in humans that we generally can't grab or grip anything with our feet and the foot has grown more elongated as a result. Some people, around 10% of the population, are even born without it. The plantaris has a short muscle belly and a long tendon and so medical students often mistake it for a nerve instead.....and it is in fact the longest tendon in the human body (a popular pub quiz question!). The plantaris tendon joins together with the gastroc and soleus to form part of the Achilles tendon.

So we now know that the gastroc and the soleus are the main workers in the calf muscle group - the gastroc in knee flexion and plantarflexion of the ankle, and the soleus in plantarflexion of the ankle. We also know that these muscles are largely responsible for pushing on the ground forcefully during running. When we plantarflex our ankle with the leg in the straight position, the gastroc plays the main role, and when we do this with the knee bent, the soleus plays the more prominent role. This point is particularly important for runners. Why?

When running, unlike walking, the knee very rarely fully extends and because of this the knee remains bent (or in flexion) when the heel strikes the ground and the forefoot pushes off. At this point, the soleus takes the lead. So, however useful a traditional calf raise is in helping to strengthen the gastroc, we mustn't forget the important role of the soleus. By exercising the calf/ankle in a flexed knee position, we can isolate it better and specifically strengthen it, and this can particularly help runners to improve their performance, running longer, faster and with less likelihood of common lower leg injuries.

From the traditional calf raise through to those exercises which challenge the soleus most.

What about a stretch?

At Porch House clinic, we have a deep understanding of muscles, tendons, ligaments, nerves and joints and we are seriously proactive in our approach to any musculoskeletal pain or injury. We have high expectations ourselves so we deliver those for you too. If you need help with a lower limb injury, or any musculoskeletal pain or injury, we use the most effective hands-on techniques to accelerate your recovery and we expect some serious results.

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