Achilles tendonitis symptoms, causes, and diagnosis

Updated: Jun 5, 2023

Recognising Achilles tendonitis symptoms is mostly about knowing where the Achilles tendon is and therefore where the pain is located. Also, when clinicians diagnose Achilles tendonitis they should listen carefully to what may have caused the pain and make the patient do some test movements to get an idea of the tendon’s pain levels and strength.

This article is an overview of the causes, symptoms, and diagnosis of Achilles tendonitis and has links to many more articles with further details on specific topics. Remember, if you need more help with an Achilles injury, you're welcome to consult one of our team via video call.

One of the most important symptoms of Achilles tendonitis that are used to diagnose it is where you feel the pain.

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

In this article:

Where is the Achilles tendon and what does it do?
Achilles tendonitis causes
Achilles tendonitis symptoms
How to diagnose Achilles tendonitis
How we can help

We've also made a video about this:

Where is the Achilles tendon and what does it do?

The Achilles tendon is the thickest tendon in your body and attaches your calf muscles to your heel bone. The calf muscles and Achilles tendon work as a unit, and you can’t train or use one without the other.

The Achilles tendon attaches your calf muscles to your heel bone.

As you walk, run, and jump, your Achilles acts like a powerful spring, propelling you forward by storing and releasing energy.

Nearly all the force you generate when pushing yourself forward goes through the Achilles tendon. Depending on what research study you read, this force has been reported to be as much as six to twelve times your bodyweight when you’re running fast.

The Achilles tendon acts like a spring when we walk, run and jump. — The Achilles tendon acts like a spring when we walk, run, and jump.

Achilles tendonitis causes

Achilles tendonitis or tendinopathy has various causes and is common in active as well as inactive people. For active people the most common cause is overload, while for inactive people it is often linked to certain medication or medical conditions.

Overload through overuse

The main cause of Achilles tendonitis or tendinopathy is overload caused by overuse (overload can also be caused in another way – see below).

Examples of activities that load the Achilles tendon:

Walking
Climbing stairs
Jogging or running (including running sports like football/soccer)
Jumping (e.g. basketball, jumping rope, etc.)
Playing sports that require quick changes of direction, lunging, and explosive movements, e.g. tennis and pickleball.

Your Achilles tendon works when you walk, run, and jump.

You can overload your tendon by overusing it in two ways:

Sudden overload is when you work the tendon too hard (compared with what it is used to), causing it to develop an injury. Any sudden increase in activities that work the Achilles tendon (walking, running, jumping) can cause this.
Gradual overload is when you don’t allow your tendon enough recovery time after training or exercise sessions. When we exercise, our bodies naturally get micro-damage in the muscles, tendons, and bones. It then repairs this micro-damage and rebuilds the relevant body parts stronger than before. If you train again before it has been fully repaired, the micro-damage may accumulate and cause overuse injuries like Achilles tendonitis.

How overload can cause Achilles tendonitis or tendinopathy.

Common ways of overloading the tendon include:

Suddenly increasing how much or how often you walk or train
Suddenly increasing the intensity of your activity e.g., how fast you walk or run, or how high you jump
Changing to a more challenging terrain e.g., doing a lot of hilly walks or runs when you’re used to flat terrain
Not allowing enough recovery time after long or intense exercise sessions
Suddenly changing to flat shoes (flip-flops, sandals) or zero-drop or minimalist sports shoes when you’re used to shoes with a slight heel, requiring your tendon to work in a larger range than what it is used to
Switching to running more on the front of your feet when you’re used to running with a midfoot or heel strike pattern will cause the Achilles to work harder than normal and may cause injury if you don’t introduce it gradually.

Overload through compression

Another way in which you can overload the tendon is through too much compression.

The area where the Achilles tendon inserts into the heel bone is naturally compressed against the bone as we move our ankle into dorsiflexion (toes move closer to the shin bone). This is usually not a problem because, given enough time, the tendon can adapt to handle the amount of compression caused by your normal activities.

Another cause of Achilles tendonitis is excessive compression through a sudden increase in dorsiflexion load.

However, if you suddenly increase the amount of compression the tendon has to tolerate, this can also cause overload and often leads to insertional Achilles tendonitis.

Activities that may contribute to compression overload:

Doing lots of ankle or calf muscle stretches and holding them for a long time
Changing to flatter walking or sports shoes
Doing lots of backwards running drills (e.g. in football/soccer).

People who have very high foot arches naturally have more compression between their Achilles tendon and the heel bone and tend to be a bit more susceptible to getting insertional Achilles tendonitis. If you have this type of foot shape, your choice of shoes and not changing to flat shoes too suddenly are even more important.

Other causes of Achilles tendonitis

Getting hit directly on the tendon
The menopause causes a drop in oestrogen levels, which in turns affects your Achilles tendon’s ability to produce and strengthen its collagen fibres, which is the main building block of a tendon.
Inflammatory conditions like gout, spondyloarthritis, rheumatoid arthritis, and psoriasis can cause tendon pain that acts in a similar way to tendonitis.
Diabetes is a common cause of tendonitis in inactive people.
Fluoroquinolone antibiotics can cause severe tendonitis and even tendon ruptures.
Statins, commonly prescribed for high cholesterol, may affect your tendon’s ability to produce and strengthen new collagen fibres, leading to tendonitis.
Having a Haglund’s deformity may predispose you to getting insertional Achilles tendonitis, but it is not in itself a cause thereof.
Prolonged increased sciatic neural tension (not very common).

Achilles tendonitis symptoms

The main symptoms of Achilles tendonitis or tendinopathy are pain and stiffness. Some people will only feel pain, others only stiffness, and others will have both.

The intensity of the symptoms may vary from just a mild discomfort to severe pain and stiffness.

It’s worth noting that studies have found that there is no correlation between the intensity of your pain and the amount of damage in your tendon. So, pain may tell you that you have an injury, but just because it is very painful does not mean that your tendon is badly injured.

What happens inside an injured Achilles tendon?

A healthy tendon is made up of many collagen fibres packed tightly in parallel. It is this parallel arrangement that makes a tendon so strong. It also contains a bit of fluid or gel-like substance and some cells between the fibres.

Healthy tendon fibres are packed in parallel with very little space between them.

When you first injure your tendon, the collagen fibres in the injured part move slightly further away from one another, and you get more fluid and various types of cells between them. At this point, your tendon may feel sore and stiff, but it is usually still pretty strong.

During the early stages of tendonitis, the collagen fibres move away from each other and more fluid and cells accumulate between them. — During the early stages of tendonitis, the collagen fibres move away from each other, and more fluid and cells accumulate between them.

If you continue to aggravate it and the injury drags on for several weeks or months, the collagen fibres may move even further out of position and eventually lose their parallel arrangement. This then causes that part of the tendon to lose its strength.

In ongoing tendinopathy or tendonitis, the collagen fibres lose their parallel arrangement.

It’s important to note that, in most cases, it’s only a small part of the tendon that is affected and that the rest of the tendon usually maintains its strength. You can regain your tendon’s full strength by following a treatment plan that usually includes carefully graded rehab exercises.

Where do you feel the pain and stiffness?

You feel the pain from Achilles tendonitis or tendinopathy on or in the tendon, and the area correlates with which part of the tendon is injured.

Insertional Achilles tendonitis – This affects the tendon where it attaches into the back of the heel bone (calcaneus).
Midportion Achilles tendonitis (the most common type) – This affects the tendon about 2 cm to 6 cm above its insertion into the heel bone.
High Achilles tendonitis (not very common) – This affects the tendon in the area of the musculotendinous junction (where the Achilles tendon and calf muscles come together).

Where you feel the pain when you have Achilles tendonitis correlates to what part of the tendon is injured.

The pain can sometimes refer to slightly under your heel, and it is quite normal for your calf muscles to also feel tight and uncomfortable.

It most commonly affects only one leg, but studies have shown that about one in three people develop Achilles pain on both sides at the same time.

The treatment plan for midportion and high Achilles tendonitis is the same, but insertional tendonitis has to be treated slightly differently. So, it’s important to identify what area of the tendon is affected.

How these symptoms start and react to rest and activity

The first time people usually notice Achilles pain is towards the end of a session (a walk, run, tennis match, etc.) or a few hours afterwards. If you’ve really overdone it, you may wake up the next day with a very painful tendon that makes you hobble for most of the day.

If you noticed a sudden, sharp pain in your Achilles tendon or it felt as if someone kicked you in the back of the leg during an activity, you’ve likely torn your tendon and should get it checked immediately. Find more information about signs and symptoms of Achilles tears here .

In most cases, however, the Achilles is stiff and/or sore first thing in the morning but then warms up as you start to move. You may find that it stiffens up again when you sit still for long.

It usually doesn’t hurt while you’re sleeping or sitting still, unless you’re applying direct pressure to the injured part of the tendon or sitting with your foot in a position that stretches the tendon.

Initially, you may find that you feel stiffness and discomfort at the start of a walk or run but that it disappears as the tendon warms up. However, the discomfort and pain may return worse than before a few hours later.

If you continue to push your training and don’t get your Achilles tendon treated, you may get to a point where the pain prevents you from doing your sport, and even just walking around the house hurts.

Swelling

You may notice a slight lump in your tendon or at your heel bone. This isn’t true swelling, as in the case of an injured joint, but rather caused by changes in the structure of the tendon (discussed above).

It is quite common to also have heel bursitis in combination with Achilles tendonitis, in which case you may notice quite a lot of puffiness and swelling around the heel bone.

Bruising

Achilles tendonitis or tendinopathy does not cause bruising. A bruise usually indicates that you’ve torn something, so please get it checked immediately if you notice a bruise.

Tingling, numbness, or burning

These are not typical symptoms associated with Achilles tendonitis. Strange sensations like numbness, tingling, or burning usually indicate that a nerve is irritated.

You may experience these symptoms if the nerve that runs close to your Achilles tendon is affected, or it can be referred pain from your lower back. The nerve injury may occur on its own or in combination with Achilles tendonitis. Your physio will be able to assess this and provide a solution.

Does Achilles tendonitis cause scar tissue?

No. Scar tissue forms in reaction to a tear or surgery. When you have Achilles tendonitis or tendinopathy, the structure of that part of the tendon changes, but it is not the same as scar tissue.

How to diagnose Achilles tendonitis

Most cases of Achilles tendonitis or tendinopathy can be diagnosed without using special tests like scans. But it is important to understand that none of these tests, not even the scans, are 100% accurate. Clinicians usually combine the results of various tests to see whether the total picture is pointing to Achilles tendonitis or whether they should also be testing for something else.

Let’s look at the basic steps clinicians use to diagnose Achilles tendonitis or tendinopathy. At Treat My Achilles, we do the first three steps via video call, and these are usually sufficient for us to make an accurate diagnosis. In a few cases, we may have to refer patients to get a scan.

Step 1: Do the history and symptoms fit?

The first step towards diagnosing Achilles tendonitis is taking the time to really listen to the patient to check whether the history they report of how the injury developed and how the symptoms are responding to different activities fits with what we would expect from Achilles tendonitis.

For example, if a patient reports that the pain started after an activity or gradually over time, that fits with Achilles tendonitis. But if they report feeling a sudden sharp pain in their tendon while running, we might suspect that they’ve actually torn their Achilles and refer them for a scan.

Or, if the pain started without them really having done anything (no increase in activity) or the pain is quite pronounced even when they are just sitting still, this may make us question whether they might have an inflammatory condition (like gout or spondyloarthritis), and we’ll refer them for blood tests.

Step 2: Squeeze or prod test

The symptoms have to be located on the Achilles tendon. So, if you are experiencing pain, it has to feel uncomfortable when you squeeze the injured part of the tendon (midportion) or press on it against the heel bone (insertional).

But this test is not 100% reliable, and you may find that someone without Achilles tendonitis also has very sensitive tendons when you squeeze them. Always compare your left and right side to see whether one is more sensitive than the other.

It is also possible to have Achilles tendonitis and not experience increased sensitivity when prodding or squeezing the tendon.

Step 3: Achilles tendon loading tests

Someone with Achilles tendonitis will usually experience increased discomfort when performing an activity that loads their tendon. Depending on your specific case (how strong you are and how sensitive your tendon is) your physio may use any number of Achilles tendon loading activities to test it, e.g.:

Double-leg calf raises (this may be sufficient for very sensitive cases)
Single-leg calf raises
Calf raises over the side of a step
Calf raises with extra weight
Hops or jumps

The Achilles loading tests your physio uses will depend on your specific case.

Sometimes these tests may not trigger your symptoms while you’re doing them, only to cause an increase in pain or stiffness later that day or the following morning. If this happens, inform your physio, because it is considered a typical sign of tendonitis, and your training plan has to take this delayed symptoms response into consideration.

It may be that these tests are pain-free, but that the patient just reports their symptoms being worsened by greater volumes of activity, e.g. after a long walk or run.

Or they may not report pain linked to activity but rather that they feel they have lost strength; this is often the case in older people, where you can see a lump in the tendon but they report little to no pain.

To make an accurate diagnosis, your physiotherapist should ask you about all the activities you do during the day, not just sport, and also use the tests that are most appropriate for you.

Step 4: Scans

Scans are useful to confirm the diagnosis if your physiotherapist suspects that your Achilles pain may be caused by something other than tendonitis or if you’re not making progress with your rehab despite doing all the right things. But scans won’t tell you how bad the injury is or how long your tendon will take to recover.

The best scans for diagnosing Achilles tendon injuries are MRI and ultrasound scans. X-rays only show bones and are not useful for assessing tendon injuries.

How we can help

Need more 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. But at Treat My Achilles we don't just value qualifications; all of us also have a wealth of experience working with athletes across a broad variety of sports, ranging from recreationally active people to professional athletes. You can meet the team here.

Find out how our online service for treating Achilles tendon injuries work.

About the Author

Maryke Louw is a chartered physiotherapist with more than 15 years' experience and a Master's Degree in Sports Injury Management. Follow her on LinkedIn and ResearchGate.

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