Seth O'Neill joins us again today to share some of his knowledge on achilles tendon problems. Seth is a lecturer in physiotherapy and is currently researching achilles tendinopathy. You can follow him on Twitter via @SethONeill. For more information, or to arrange an appointment with Seth at his clinic in Nottingham see his profile page.

“Prevention is better than Cure”

Hopefully you're familiar with the term tendinopathy, it is an umbrella term meaning a problem with a tendon, and most tendon disorders show degenerative issues rather than typical inflammatory issues. Have a read of Tom’s other excellent blogs on tendon disorders for some further background. This blog is aimed at runners to help them understand how problems are triggered and how to prevent them. It is not meant as a full explanation of Achilles Tendinopathy, however I will be back with some further info about my concept on Achilles tendinopathy development and successful treatment at a later stage.

This blog is going to attempt to answer two common questions asked by patients: “why did I develop my Achilles tendinopathy” and “how can I stop this happening in the future”. The first question effectively formed a recent research question I attempted to answer as part of my PhD into Achilles Tendinopathy. The study aimed to develop a consensus of opinion from leading international tendon experts about the risk factors for Achilles tendinopathy in athletic/active individuals and also sedentary/inactive individuals. We attempted to develop this consensus because the current published literature often expresses a particular risk factor whilst another study shows the opposite.

Risk factor studies are sometimes difficult to make head or tails of, there are two main types; prospective ones that aim to assess a population group and let them get on with life and see who develops the disease and then association studies which take a population with the issue (Tendinopathy) and then compare them with healthy groups to assess whether the factor has a higher incidence in the diseased group. This latter type has many pitfalls as we cannot ascertain whether the factor is the “chicken” or the “egg”.

In order to understand risk factors we have to understand the pathology involved in Achilles Tendinopathy, this is a slightly complex issue but I think it can be simply understood as an overuse condition of the tendon – it’s worth listening to the excellent BJSM and Physioedge podcasts on Tendinopathies by world leaders like Professor Jill Cook, Dr Alison Grimaldi and Dr Johnathon Rees. I freely admit other systems are at play but the general pathology and management strategies are best fitted with a degenerative model.

So how would we overload the Achilles Tendon and trigger the cellular reaction and chemical cascade that leads to Achilles Tendinopathy?

To understand this we must consider what happens during exercise and recovery. During exercise we are effectively “wearing” our bodies out. This is critical as this “wear” triggers chemical reactions in the body that make it adapt (bigger muscles, fitter hearts etc – this is not a bad thing, it is essential for improvements associated with training). Whilst we rest (sleep) our body repairs and recovers.

The balance between wear and repair is critical, anything that increases the rate of wear above the rate of repair starts the tissue in a degenerative overload process, if this is allowed to continue for long periods the Achilles will gradually degenerate to a level that is likely to trigger pain. Jill Cooks model of tendinopathy explains the clinical presentation more specifically by breaking groups into Reactive (really irritated and stirred up with minimal activity), disrepair, (niggly and irritated if exercising above a certain level) and degenerative (full blown longterm changes). The effects of overload on tendons has clearly been shown to link to tendinopathy development in various animal models of tendinopathy.

(Now I fully appreciate that “healthy” pain free people sometimes have tendons that look like a tendinopathy on imaging, I think given the right stimulus these tendons would become symptomatic, this view is supported by some studies.)

From this understanding of wear and repair we can start to consider the likely triggers of tendinopathy in athletic individuals, the most frequently reported in the literature and found in our consensus study was previous Tendinopathy, previous injury and changes in training – e.g. increasing mileage, speed, distance or intensity by doing hill reps or similar speed work. Remember Tom’s hamstring tendinopathy occurring with his hill reps over several days!

Risk factors are normally split into several groups commonly called intrinsic and extrinsic factors. Intrinsic factors relate to internal issues whilst extrinsic factors relate to external elements (see factors below as it makes this clear) for athletes these are often about activity levels and in my opinion offer an easy area to target to prevent Achilles Tendinopathy.

Intrinsic risk factors

  • Previous Lower limb Tendinopathy
  • Recent Injuries
  • Age
  • Gender
  • Muscle power/Strength
  • Reduced Dorsiflexion
  • Foot Pronation
  • Weight gain due to layoff/holiday


  • Changes in Loading, returning after closed season or injury, or change in training technique
  • Training Errors
  • Recent Injury to Lower Limb (same side)
  • Activity Levels

Training errors

  • Sudden changes in activity- ramping up or recovery periods/lay off
  • Changes in Loading- type of activity
  • Recent alteration in training. e.g. for an event/competition
  • Duration of Training- Time per session
  • Frequency of training
  • Weekly Distance

(The above is based on my Delphi study)

This list is not full and has several major factors that I’ll come back to a some point in the future.

You will notice from these factors that several (age, gender, previous injury and tendinopathy) are not modifiable. However of the modifiable issues (extrinsic factors) the most common issue discussed in the literature is training error’s, normally this is excessive or too rapid increases in distance, or training prior to full recovery, this is the hard area to determine as your legs often feel recovered but they aren’t. Most athletes or recreational runners I treat end up training prior to full recovery (normal loading) and I think it is this frequency that really triggers the issue. Some individuals may require longer than normal for the tendon and muscle to recover after activity, and maybe quicker. This may explain why certain metabolic conditions can link to tendinopathy.

People overtraining prior to tendinopathy development is often clearly demonstrated during the rehab period, as many of our patients achieve PB’s on their first return race. This fact clearly highlights that they were overtraining prior to injury (normally without knowing it) and that they need to get a better balance of their wear:repair threshold.

Picture source

Out of the identified risk factors the main controllable factors are the extrinsic factors linked to training intensity. The current consensus in the literature is increases in 10% per week (distance or intensity) is generally considered safe. A lot of runners increase distances far faster and to a greater extent than this and end up doing so the day after a previous training session. This recipe clearly puts the tendon at risk of being overloading and not being able to repair in the timeframe allowed. My other thought is this repair process is probably lower as people get older, since resting repair rates reduce a little, this probably reduces the “safe” zone for increasing training levels. This may explain why age is such a high risk factor for Achilles Tendinopathy, and why older patients do not respond as well to the current rehab methods.

Other factors for athletes to consider:

Anti-Biotics from the fluroquinolone family are linked to Achilles Tendinopathy and Achilles ruptures, this has been shown in numerous studies. Ideally if you are taking antibiotics you need to consider how you are training and the degree of other risk factors. It may be beneficial to do more bike work or potentially reduce loading using water based activities. I have to state there is very little evidence about what is the right amount of activity to do so it is very individual.

Obesity, waist circumference and adiposity have been linked to Achilles tendinopathy. The link is thought to be due to circulating cytokine levels that create a cellular reaction and affect the tendon. Obviously changing this is a little difficult. The consensus seems to be regular exercise of any description helps reduce this and may promote healing/prevent tendinopathy.

Take home message: Not all risk factors are modifiable, of those that are, training frequency and increases in distance are probably the easiest to control in the fight to prevent Achilles Tendinopathy.

I have purposefully passed over several modifiable factors that I aim to cover at a future day, they currently form part of an article I am writing and I would like to wait until that is submitted and accepted somewhere first.

If you are interested in participating in a national survey of Achilles Tendinopathy then please follow this link. It will take 7 minutes to complete and needs Healthy and injured Runners.


  1. Hi Tom and Seth, I know this is an Achilles post, but just a quick query regarding the hamstring hill graph.
    I see you have made a note about the increase in hip flexion resulting in increased compressive loads. What are your thoughts about the increase in forward trunk flexion that occurs during hill running?

  2. Hi guys I think I’m just what your looking for im currently awaiting mri results(25thfeb) on both achilles !!! It will be two year this June ??? It started in my right and now my left is the worst !!! It started with a sharp pain in my right got the usual rest ice etc etc then physio each time I broke down until the physio said he couldn’t do anymore for me ? Was referred to specialist first time nothing wrong ???after a few month was referred to a Mr torres at the freeman Newcastle !!!I’ve had ultrasound and an mri on both legs ?? I’ve got non insertion al achilles tendonopathy and im awaiting results

  3. Great article. Just wondering why you have included pronation as a risk factor? Seems to be constantly debunked nowadays…
    Very limited evidence dynamic foot function is a risk factor for Achilles tendinopathy & overuse injuries:

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