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Isotonic exercises – How to use them for treating Achilles tendonitis

Updated: May 31, 2023

Achilles tendinopathy exercise series:


In this article, we discuss how isotonic exercises (a combination of eccentric and concentric contractions) can help to restore your muscle power and tendon strength, which are essential when rehabilitating an Achilles tendinopathy. Remember, if you need more help with an Achilles injury, you're welcome to consult one of our team via video call.

What type of exercise works for treating Achilles tendinopathy and why? - Isotonic exercises

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:

Ali also discusses isotonic exercises in this video:

What are isotonic exercises?

Isotonic exercises combine concentric (where the muscle shortens) and eccentric (where the muscle lengthens) contractions. An example of this is the classic calf raise exercise associated with Achilles tendinopathy rehab, where you slowly lift yourself up on your toes (concentric phase) and then lower yourself down (eccentric phase).

Isotonic heel raise exercises strengthens both the concentric and eccentric phases.
Isotonic heel raise exercises strengthen both the concentric and eccentric phases.

How can isotonic exercises benefit an injured Achilles tendon?

It strengthens your tendon

When you have Achilles tendinopathy or tendonitis, the tendon's capacity to cope with the forces generated by your sport or daily activities (like walking and stair climbing) is reduced. The calf muscles are also affected. This means that your Achilles tendon and calf muscles need to be strengthened to recover this lost capacity. Isotonic heel raises, especially when combined with progressively heavier weights, have been shown to effectively improve and restore the capacity of injured tendons.

A tendon is made of many strands of collagen fibres, which are arranged in lots of bundles. Imagine many bundles of spaghetti in parallel with each other. In a tendinopathy, not all the bundles, and indeed not all the fibres in a specific bundle, are affected; many of them stay healthy.

As with all cells in the body, tendons also follow a natural cycle where old collagen cells in our tendons are replaced by new ones. Exercise promotes this cycle and therefore promotes the creation of healthy collagen – hence why we can use exercise to strengthen our tendons.

The exact theory of how strength training heals a tendinopathy is unknown. One school of thought is that, in some instances, the injured collagen fibres are replaced by healthy ones. There is evidence that strength training can reduce the ingrowth of blood vessels and the thickening that are typical of an injured tendon. But there is also evidence that some tendons still show signs of injury even after regaining full strength and function.

Another theory suggests that the injured fibres remain injured, but that the new, healthy collagen fibres that form in reaction to the strength training help to support these injured fibres (like a brace or splint), therefore causing increased strength and function and less pain.

It uses the full movement pattern

When we move, we use both concentric and eccentric calf muscle contractions. As opposed to isometric exercises and eccentric-only calf raise exercises, isotonic exercises strengthen both these types of contractions. They are therefore better suited to restore your full calf and Achilles function.

When should I use isotonic exercises for Achilles tendinopathy?

We usually try and start isotonic exercises as soon as possible, but this answer really needs to be individualised for you. Isotonic exercises can be done in a variety of ways depending on the specific situation, e.g. on two feet, on one foot, with extra weight, over the side of a step, or just to floor level.

At, we assess you to find your starting point; what is your tendon’s current capacity and what can you do without increasing your symptoms? Our choice of exercises is also guided by your end goal, which could be to walk your dog, jogging around the block, an ultramarathon, or anything in between.

Other factors, such as your general health and medications you take (statins, antibiotics), can also affect what exercises we prescribe and how long it takes to progress from easier to more challenging exercises.

For instance, if your tendon is still very painful and easy to flare up, we may start you off with low-load isotonic exercises done on both legs. If it is the mid-portion of your Achilles that is affected, we may get you to do them over the side of a step. However, if you have insertional Achilles tendinopathy, we will very likely start you off doing your heel raises only to floor level.

Regardless of where you start, your programme will have to be progressed over time (using increasingly heavier weights) until your tendon has regained the strength and capacity it needs to do the activities you want to do.

The main thing to remember is that a decrease in symptoms may not be the first thing you notice when taking up these exercises. An indication that your Achilles is getting better will be when you start to find your exercises easier and when you’re able to progress them without your pain increasing. It’s usually only after a few weeks of progressing them that you start to notice a greater reduction in symptoms.

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.

Meet the TMA physios

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.

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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.


  1. Alfredson, H., Pietilä, T., Jonsson, P. and Lorentzon, R., 1998. Heavy-load eccentric calf muscle training for the treatment of chronic Achilles tendinosis. The American Journal of Sports Medicine, 26(3), pp.360-366.

  2. Beyer, R., Kongsgaard, M., Hougs Kjær, B., Øhlenschlæger, T., Kjær, M. and Magnusson, S.P., 2015. Heavy slow resistance versus eccentric training as treatment for Achilles tendinopathy: a randomized controlled trial. The American Journal of Sports Medicine, 43(7), pp.1704-1711.

  3. Cook, J.L. and Purdam, C.R., 2009. Is tendon pathology a continuum? A pathology model to explain the clinical presentation of load-induced tendinopathy. British Journal of Sports Medicine, 43(6), pp.409-416.

  4. Silbernagel, K.G., Thomeé, R., Eriksson, B.I. and Karlsson, J., 2007. Continued sports activity, using a pain-monitoring model, during rehabilitation in patients with Achilles tendinopathy: a randomized controlled study. The American Journal of Sports Medicine, 35(6), pp.897-906.


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