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Why do I have a lump in my Achilles tendon?

Updated: Jun 1, 2022

Have you noticed a painful lump in your Achilles tendon? That lump is a tell-tale sign that you’ve likely got Achilles tendonitis or tendinopathy. In this article I’ll explain what happens to your tendon when you injure it and why it forms this lump.

Injured runners sitting on a track inspecting his Achilles tendon and asking: "Why do I have a lump in my Achilles tendon?"

In this article:

  • What the Achilles tendon normally looks like

  • What happens in your tendon when you injure it?

  • How to get rid of the lump in your tendon

I've also explained this in this video.

What the Achilles tendon normally looks like

The Achilles is a thick broad tendon that attaches the calf muscles (Gastrocnemius and Soleus) to your heel. When the calf muscles contract they pull the Achilles tendon tight which in turn makes your foot point down. This is the action that allows you to push off the ground when you walk, run and jump.

If you look at the Achilles tendon under a microscope you’ll notice that it's made up of thousands of collagen fibres that are packed closely together next to each other with very little space between them. These fibres are all aligned in the same direction. This is important because it’s what makes the Achilles tendon so strong!

Healthy Achilles tendon with fibres closely packed and small cells.

Do you remember playing with string at school? If you had a single thread, you could easily break it. But as soon as you put a few pieces of string next to each other, it was nearly impossible to break.

Healthy Achilles tendons are extremely strong and stiff. Unlike muscles, we want tendons to be stiff because then they work better. This is why doing stretches for Achilles tendinopathy is really not that useful.

If you look closely at the picture above you’ll also notice that there are also a few small cells in the tendon.

What happens in your tendon when you injure it?

The pictures below shows what happens in the Achilles tendon when you injure it.

Picture B is of a tendon that has been sore for a few days. Can you see that the collagen fibres are now starting to move away from each other and there’s more white stuff in between them. There are also a lot more cells in the tendon than normal.

Microscopic image of an injured Achilles tendon. The fibres are moving away from each other and there are a lot more cells in the tendon.

Picture C is a microscopic image of what a tendon looks like when it has been sore and injured for several months. The collagen fibres are no longer aligned next to each other but more of a mess, like spaghetti in a bowl, and you now have large cells (of the wrong kind).

This tendon has been injured for a long time. The fibres are no longer aligned next to each other and the cells have changed shape and size.

If you look at the tendon under ultrasound scan, you’ll also notice that there are several small blood vessels growing into the painful part of the tendon. Healthy tendons don’t have blood vessels growing into them.

The end result of all of these changes (fibres moving further apart, cells becoming bigger, blood vessels growing) is that your tendon develops the lump that is associated with tendonitis. The tendon is now softer and more elastic and doesn’t work as well as before.

How to get rid of the lump in your tendon

Achilles tendinopathy or tendonitis develops when you over-strain or overload your tendon. The only way to help your tendon to recover and get rid of the lump in your Achilles is through managing the load that you put through your tendon on a daily basis.

What do I mean with load? Load refers to all the work you ask the tendon to do in a day. This includes walking, running, jumping, heel raise exercises and ANY other activity that uses the Achilles.

That’s why our first step when treating Achilles pain is always to have an in-depth discussion with our patients to get a complete picture of their normal training regime and their other daily activities e.g. work etc. Don’t think that you have to stop all your training either – most of the time we find that we can just adjust the volume or intensity to a level that allows your Achilles to recover while you maintain your fitness.

Rest alone isn't helpful either. It may decrease the pain a bit, but it doesn’t actually strengthen the tendon. You need to do carefully graded strength training exercises to get the body to replace the injured tendon cells with new strong ones, that are packed closely together. It’s a similar process as to when you go to the gym and build big muscles.

Follow this link to read more about our expert online physio service for treating Achilles tendon pain.

This is also why passive treatments like massage and dry needling isn’t really that useful for this condition. Yes, it may make your calf muscle feel more relaxed and less painful but massage doesn’t change anything inside the tendon. Just like you can’t massage your muscles stronger, you also can’t rub the lump out! The cells has to change and that can only be done through load management.

What exercises should you be doing? There is no one-size-fits-all and personally I find that I have to adjust what I prescribe for every person, taking their normal training regime etc. into consideration. What works for one person’s Achilles may cause overload in the next.

Let me know if you have any questions! Need more help with your injury? You can read more about our online physio service for treating Achilles tendon pain here.

Best wishes


Maryke Louw

About the Author:

Maryke Louw is a chartered physiotherapist and holds an MSc in Sports Injury Management. You can follow her on LinkedIn, Facebook, Twitter or Instagram.


  1. Cook JL, Rio E, Purdam CR, et alRevisiting the continuum model of tendon pathology: what is its merit in clinical practice and research?British Journal of Sports Medicine 2016;50:1187-1191.

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