Bent-knee calf raises – How to target the soleus part of the Achilles tendon

The bent-knee calf raise exercise is an excellent way of targeting your soleus calf muscle and the part of the Achilles tendon that originates from it. In this article, we look at various types of bent-knee calf exercise and what the latest research implies for their use in Achilles rehab programmes. Remember, if you need help with an Achilles injury, you're welcome to consult one of our team via video call.

The terms tendinitis, tendonitis, tendinosis, and tendinopathy mean the same thing for all practical purposes, and we use these interchangeably in most of our articles.

In this article:

1. Why use bent-knee calf raises?

2. Types of bent-knee calf exercise

3. Who needs to do bent-knee calf raises?

4. How we can help

Why use bent-knee calf raises?

Anatomy recap

Your Achilles tendon attaches your two calf muscles (gastrocnemius and soleus muscles) to your heel bone.

Rehab exercises (typically calf raises) to strengthen an injured Achilles tendon ideally need to make each of these muscles work. These muscles work as a unit with the Achilles tendon. So, the more strength we get in both muscles, the more robust the Achilles tendon is and the more it can cope with various activities that you may be finding painful or difficult or struggling to do at the moment.

Bent-knee calf exercises target the soleus

However, the classic calf raise exercises prescribed for Achilles injury rehab are done with straight knees, and these target mostly the gastrocnemius. Fair enough, as it is the bigger of the two calf muscles.

Straight-knee calf raises work the gastrocnemius harder.

Bent-knee calf raises, on the other hand, bring the soleus into play by targeting mostly this smaller muscle.

Types of bent-knee calf exercise

There are a variety of bent-knee calf exercises that you may be given at various levels of difficulty, and people are given different ones for many reasons. These include:

• personal preference

• how strong and fit your tendon is at the time

• how it's coping with daily activity – so, how robust it is

• your symptoms

• what access to equipment you have

• how long you've been having this problem for

• and what strength training you've done before.

Below are three of the most common ones. All of them can be varied in terms of things like the number of sets and repetitions, how much weight is involved, whether you’re going faster in one direction than in the other, and whether you use one or two legs.

This is why it’s important, when you're looking at your own case, to speak to somebody who is able to find out what’s the best starting point for you and how to progress from there.

Leg press machine

One option is to use the leg press machine in a gym. Typically, you would put your feet onto the plate of the leg press machine and push, bending and straightening your knees to target muscles like the glutes and quads.

For a bent-knee calf exercise that targets the soleus, you would keep your knees bent and push the plate away from you by pointing your toes and then bringing it back again, preferably in a slow, controlled way, by returning your feet to their normal position.

Seated bent-knee calf raises

With seated bent-knee calf raises, you sit on a chair with knees bent 90 degrees and in line with your heels. You lift your heels and then slowly lower them back down.

This exercise can become quite easy after a while, and you can make it harder by putting some weight on your knees or lap. You can also use the Smith machine in the gym for doing seated bent-knee calf raises with various weight settings.

Standing bent-knee calf raises

The really common standing calf raise exercise is done with your knees bent and going up and down on your toes, keeping your knees bent the whole time. This can be done on two legs or one leg and without or with added weight.

Who needs to do bent-knee calf raises?

Not everybody with an Achilles injury needs bent-knee calf raise exercises. Some people may never need them at all. For others, these exercises simply may not work.

The latest research on who might benefit most from bent-knee calf raises came out in 2022. A group of researchers based in Belgium and New Zealand used ultrasound to measure which part of the Achilles tendon takes the most strain (“peak strain”) during several types of rehab exercise. This matters, because most Achilles tendinopathies affect only a small part of the tendon.

The bent-knee calf raise they used in the study was a standing one where you go up on your toes on two feet and then lower yourself down on only the injured side.

The researchers used the standing bent-knee calf raise where you lift up on both legs and lower on one leg.

First, the study confirmed that this exercise placed peak strain on the part of the Achilles tendon that attaches to the soleus muscle.

The researchers further found that the peak strain happened in the mid-portion part of the tendon (so, somewhat higher than the heel bone), which is one of the most common areas for Achilles tendinopathies to occur.

This might be a clue as to why people with mid-portion Achilles tendinopathy who started with bent-knee calf raises right away may have found them uncomfortable and/or painful and therefore abandoned them. The bent-knee calf raises placed too much strain on the injured part of the tendon while it was still in a sensitive state – it’s a bit like prodding a fresh bruise.

For these people – if there isn’t a way of adjusting the bent-knee calf raises to make them feel a bit more comfortable in that first instance – it may work to defer them until later in their rehab, when their tendon is a bit stronger.

Bent-knee calf raises may be especially useful for people who have only been doing the more conventional straight-knee calf raises for their Achilles tendinopathy and have not seen any improvement for quite some time, especially if it’s a mid-portion tendinopathy.

You won’t get any stronger (and this is true for any muscle or tendon) if you keep the exercise difficulty at the same level forever. You have to make your rehab exercises progressively more difficult, and adding in the bent-knee calf raises is one way to do this.

However, if you have insertional Achilles tendonitis, bent-knee calf raises may increase your pain, because it pulls the tendon tighter against the heel bone where it inserts, increasing the compression at the injured part of the tendon (“prodding that bruise” again).

How we can help

Need help with your Achilles injury? You’re welcome to consult one of the team at TMA online via video call for an assessment of your injury and a tailored treatment plan.

We're all UK Chartered Physiotherapists with Master’s Degrees related to Sports & Exercise Medicine or at least 10 years' experience in the field. All of us have a wealth of experience working with athletes across a broad variety of sports and ranging from recreationally active people to professional athletes. You can meet the team here.

About the Author

Alison Gould is a chartered physiotherapist and holds an MSc in Sports and Exercise Medicine. You can follow her on LinkedIn, Facebook, Instagram or Twitter.

Reference

Funaro A, Shim V, Crouzier M, Mylle I, Vanwanseele B. Subject-Specific 3D Models to Investigate the Influence of Rehabilitation Exercises and the Twisted Structure on Achilles Tendon Strains. Front Bioeng Biotechnol. 2022 Jul 6;10:914137.