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What causes Achilles pain when running?

Understanding what causes Achilles pain when running will make it easier to treat and prevent happening again.

The causes of Achilles tendonitis all appear to be related to excessive stress being transmitted through the tendon. Weak calf muscles, poor ankle range of motion, and excessive pronation have all been connected with the development of Achilles problems. The upshot is that all of these factors, plus training volume and so on, result in damage to the tendon.

The Achilles tendon attaches the calf muscle to the base of the heel and is there to transfer the forces generated by the calf muscles. The Achilles tendon is made up of small fibre proteins called collagen and looks a lot like a bungee cord with the elastic fibres all aligned together.

The job of the tendon is to attach muscle to bone and transfer the forces applied to them by the muscle to facilitate movement. Because of that they are designed to be very strong and will become gradually thicker and stronger over time with any increased stress on them. This is key to understanding the cause of Achilles pain when running later on.

What is Achilles tendonitis (Tendonitis)?

Achilles Tendonitis is the medal word used to describe Achilles pain and its cause. Tendonitis means inflammation of the tendon. “Itis” at the end of the word means “inflammatory disease”.

Initially, tendonitis will start as a dull ache or stiffness at the start of a run or after you finish, but typically eases off when it is warm. You may experience an increase in these symptoms when running faster, running uphill or wearing a more minimalist shoe. This is because all of these force you to run more on the balls of your feet, putting additional strain on the calf muscle and Achilles tendon.

If you continue to run over a period of time then this pain will continue to intensify. It will be sharper, will take longer to ease off and you will most likely find it starts to impact on your running gait.

Why does this cause Achilles pain?

At the start of this piece, I mentioned that tendons will naturally thicken over time to respond to the forces being applied to them. If this adaption occurs as part of a graduated strength and training program then it will not cause any concern.

The issue is a sudden increase in intensity where the tendon adapts faster than it should and in turn loses some of the elastic properties and shortens slightly. Additionally, it causes Achilles pain when running if you have a muscle imbalance and more of the forces are going through either the left or right leg. This can be a result of an old injury of returning after a period of rest.

How to treat Achilles pain.

How to prevent Achilles pain.

What causes Achilles pain when running?

There are two classifications of causes of Achilles pain in runners

  • Intrinsic factors – You as the runner.
  • Extrinsic factors – Your environment.

Intrinsic factors: 


Biomechanical abnormalities, such as leg length discrepancy, ankle restrictions or the most common is overpronation (flat feet).

Overpronation is extremely common and something that can be corrected with the right footwear, insoles and/or exercises to work on the small muscles of the foot.

As you can see from the illustrations below, overpronation causes the Achilles tendon to bow. This means that there is an abnormal loading of the tendon which will, over time, cause uneven thickening irritation and inflammation to the tendon.

Normal foot alignment



Strength imbalance. This normally occurs after an injury or a long period of rest where you will experience some deconditioning.

As we all have a dominant side, if you do not work to strengthen both legs unilaterally to the same level then this imbalance will only increase over time.

The average number of heel strikes in a mile is 1600, so you can see how easy it is for this to occur.


Systemic conditions. Sadly, most of the time this are biological factors that we cannot avoid such age.

There are some conditions like inflammatory arteriopathies, corticosteroid use, diabetes, hypertension and obesity that can be managed. Having these conditions will not necessarily prevent you from running but it is always best to do so under the guidance of your doctor or a medical professional.

Extrinsic factors:  


Overloading and training errors such as a sudden increase in training intensity or duration without the proper strength training to support this.


This can cause tight or fatigued calf muscles, which transfer too much of the burden to the Achilles when running and will cause pain.

Additionally, the introduction of hill running or sprints, mainly on the incline, will put an additional stretch on the calf and Achilles whilst simultaneously increasing the load.


Incorrect or old footwear. You should replace running shoes every 300-500 miles which loosely equates to every 3-6 months.

Stiff running shoes will force the ankle and Achilles to twist triggering Achilles pain when running. It is important to have your feet and gait analysed if possible to determine the correct footwear for your running style and foot mechanics.

There was a spike in Achilles pain when running as more people shifted to a minimalist shoe. While there are great benefits in these shoes, they are not for everyone. It is largely dependent on your running style (if you are a forefoot runner), your level of running ability and fitness.

If you start experiencing pain in the Achilles region, stop running.

“An irritated Achilles tendon can turn into a more serious tendinosis and partial or complete tear of the Achilles in very rapid succession. You don’t want to make a bad injury worse by running through it.”

Jordan Metzel M.D.

Sports medicine physician at the Hospital for Special Surgery in New York City Runner’s World’s IronStrength workout

How to prevent Achilles pain when running.

How to treat Achilles pain when running

About the author

Cameron is a former professional rugby player who broke his back in 2007. He is a qualified physiotherapist with two degrees in Sports Science and Physiotherapy. Before Riixo he worked for the UK national health service (NHS), in professional sport and the British army. Read about his story.

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