What Might Predispose You to an Achilles Injury?
Key findings: 60-second read
- Stronger ankle control protects against Achilles pain - runners with higher ankle inversion moment (the force that rolls the ankle outward) had 67% lower risk of developing Achilles tendinopathy.
- Feet that turn out slightly may be protective, not harmful - runners with less external foot rotation had 120% higher risk, suggesting some natural foot turn-out is okay.
- Higher running mileage significantly increases risk - each extra 12.5 km per week raised injury odds by 67%. More running is not always better.
- Foot strike pattern (heel vs forefoot) does NOT predict injury - common advice to change how your foot lands may be unnecessary for preventing Achilles problems.
- Hidden issues higher up (back, hips, ankle stiffness) can set you up for trouble - a stiff lower back, tight ankles, or flat arches can change how your whole leg moves, putting extra strain on the Achilles tendon.
If you are a runner, you have probably heard horror stories about Achilles tendinopathy. It is that nagging pain at the back of the heel that just will not go away. It can sideline you for months. And despite all the advice you have heard - change your foot strike, stretch your calves, ice after running - it keeps coming back.
A major new study published in the British Journal of Sports Medicine (Jandacka et al., 2026) followed 911 adults (528 runners) for one full year. Researchers measured their running form in a lab, tracked their running volume with Fitbit devices, and confirmed Achilles injuries with actual medical doctors (not just self-reported pain).
The findings challenge a lot of what runners think they know about preventing Achilles problems. And they point to some surprising protective factors that you may not have considered.
"A higher peak ankle inversion moment during the stance phase decreased the odds of developing Achilles tendinopathy, while a lower peak ankle external rotation angle and greater running distance increased the odds of onset."
On this page
What the study found
The researchers looked at dozens of different measurements of running form. Most of them did NOT predict Achilles injuries. But two biomechanical factors stood out as strongly protective:
- Ankle inversion moment - the force that rolls your foot outward (towards the little toe side) during the part of your stride when your foot is on the ground
- External foot rotation - how much your foot naturally points outward (like a duck's foot) during your running stride
Runners who had higher values of both of these were significantly less likely to develop Achilles tendinopathy. The study also found that running more kilometres per week significantly increased risk, while foot strike pattern (whether you land on your heel, midfoot, or forefoot) made no difference at all.
Ankle inversion moment: the protective factor
Let me explain what "ankle inversion moment" means in everyday language.
When you run, your foot goes through a natural rolling motion. It rolls inward slightly (eversion) when you land, then rolls outward (inversion) as you push off. The "inversion moment" is the force that creates that outward rolling motion.
What the study found: Runners with higher ankle inversion moment (stronger outward rolling force) had a 67% lower risk of developing Achilles tendinopathy. That is a huge protective effect.
Why does this matter? When your foot rolls outward properly during push-off, it helps absorb impact and distribute forces. Without enough inversion moment, your Achilles tendon may end up taking more load than it should, especially in the sagittal plane (the forward-backward direction where the Achilles is already under high stress).
Think of it like this: your ankle is designed to move in multiple directions. If it only moves forward and backward (like a hinge), all the force goes through the Achilles. But if it also moves side-to-side (inversion/eversion), that force gets spread out. More inversion moment means better side-to-side control, which takes pressure off the Achilles.
Foot rotation: turned out is not bad
Many runners have been told that their feet should point straight ahead when they run. If your feet turn outward (like a duck), someone has probably told you to correct it.
This study found the opposite. Runners with less external foot rotation (feet pointing straighter) had a 120% higher risk of Achilles tendinopathy. In other words, some natural foot turn-out appears to be protective, not harmful.
Why does this matter? When your foot is externally rotated (turned out slightly), it changes the angle of pull on the Achilles tendon. This may reduce the stress on specific parts of the tendon (particularly the lateral subtendon) and distribute load more evenly.
This does not mean you should deliberately run with your feet splayed out. But if you have a natural degree of external rotation that is not causing other problems, forcing your feet straight may be doing more harm than good.
The challenge here is to try to figure out what degree is "natural" and what is an abnormal compensation for ankle and hip restrictions.
"A 6° reduction in peak external foot rotation angle was linked to approximately a 120% increase in the odds of Achilles tendinopathy. In other words, less external rotation (feet pointing straighter) was associated with higher injury risk."
Running volume: more is not always better
This finding will not surprise many runners, but the numbers are striking. Each additional 12.5 km per week (about 7-8 miles) increased the odds of developing Achilles tendinopathy by 67%.
In this study, the runners who developed Achilles injuries were running a median of 19.7 km per week before their injury. The uninjured runners averaged just 5.7 km per week.
Why does this matter? The Achilles tendon needs time to recover and adapt after running. Research shows that the tendon requires about 1.5 to 3 days for collagen regeneration following physical activity. High weekly volumes without adequate rest days may not allow enough time for this "supercompensation" phase.
Previous research has shown that running more than 40 km per week in middle-aged runners leads to structural changes in the Achilles tendon visible on MRI. That does not mean 40 km is a hard limit, but it is a warning sign to be careful.
Practical takeaway
"An increase of 12.5 km in weekly running distance was associated with a 64% increase in the odds of Achilles tendinopathy. Monitor your training volume, especially if you are a high-mileage runner."
Foot strike: heel strike vs forefoot strike - does it matter?
You have probably heard advice that forefoot striking is better for your Achilles, or that heel striking is bad, or that you should aim for a midfoot strike. This study found no association between foot strike pattern and Achilles tendinopathy risk.
In the injured group: 78% were rearfoot strikers, 17% midfoot, 4% forefoot. In the uninjured group: 83% rearfoot, 11% midfoot, 5% forefoot. The difference was not statistically significant.
Why does this matter? Changing your foot strike pattern is hard. It takes months of practice and can introduce new injuries (like metatarsal stress fractures or calf strains). If you are pain-free with your current foot strike, this study suggests you do not need to change it for Achilles prevention.
The authors note that previous studies linking midfoot strike to Achilles tendinopathy were retrospective (looking backward). Runners with existing Achilles pain may have changed their foot strike to reduce pain, creating a false impression that midfoot strike causes injury. Prospective studies like this one (looking forward) are more reliable.
"The results of our study demonstrate that footfall pattern (rearfoot, midfoot or forefoot) is not associated with a higher risk of developing Achilles tendinopathy. If you are pain-free with your current foot strike, changing it may introduce new injury risks without clear benefit."
From my clinical experience: the hidden chain from back to ankle
This study focused on what happens at the ankle during running. But in my 20 years of clinical practice, I have learned that problems rarely start where the pain is. The Achilles tendon is often the victim, not the culprit.
Let me explain what I mean. Your body is a chain. When one link is stiff or weak, other links have to work harder. Here is what I see over and over again in runners with Achilles tendinopathy:
Lower back stiffness. Your lumbar spine controls how your hips move, the nerves supply the rest of your leg. If your lower back is stiff (often from too much sitting, poor posture, or previous injuries), compensations can occur. This can change how your legs swing and how your feet land. I have lost count of how many runners with chronic Achilles pain had a stiff lower back that no one had ever looked at.
Ankle joint stiffness (lack of dorsiflexion). If your ankle cannot bend enough (especially dorsiflexion - bringing your shin forward over your foot), your body will find a way to compensate. Sometimes that means turning your foot out. Sometimes it means your heel lifts off the ground early. Sometimes it means your knee and hip move differently. A stiff ankle can change how we load the Achilles tendon.
Feet that turn out (external rotation). Here is where this study's findings are really interesting. The study showed that some external rotation is protective. But what is "normal"? Too much external rotation (like a duck walking) can be a problem, especially if it is driven by stiffness elsewhere (like the ankle or hip). The key question is not "are your feet turned out?" but "why are your feet turned out?" Is it a natural, healthy rotation? Or is it a compensation for a stiff ankle or a tight hip?
Poor arch function (collapsed arches or flat feet). Your foot arch is not just a passive structure. It is designed to absorb shock, store energy, and help you push off. When the arch collapses too much (over-pronation), it changes the angle of pull on the Achilles tendon. The tendon has to work at a different angle, which can create uneven stress and lead to degeneration over time. On the flip side, a very rigid, high arch that does not move enough can also be a problem because it does not absorb shock well.
Here is the clinical reality that this study does not capture: many runners with Achilles tendinopathy have multiple issues. A stiff lower back + poor ankle mobility + flat arches. Each one alone might be manageable. But together, they create a cascade of compensations that may eventually overload the Achilles tendon.
This is why simply telling a runner to "strengthen your calves" or "stretch your Achilles" can fail. You are treating the symptom, not the cause. If the Achilles is overworked because your ankle is stiff and your back is locked up, no amount of calf stretching will fix that.
A clinical perspective
"In my 20 years of practice, the runners who develop chronic Achilles problems almost always have issues higher up the chain. A stiff lower back, poor hip control, or limited ankle mobility forces the Achilles to do work it was never designed to do. You cannot treat the tendon in isolation - you have to look at the whole body."
What you can do to protect your Achilles
Based on this study and clinical experience, here is my practical advice for runners:
1. Do not obsess over foot strike. If you are running pain-free, keep doing what you are doing. Changing your foot strike is not evidence-based for Achilles prevention.
2. Respect the 10% rule (or less). Increase your weekly mileage by no more than 10% per week. The study found that higher volume significantly increases risk. Give your tendons time to adapt.
3. Check your ankle mobility. Can you bring your knee over your toes while keeping your heel down? If not, you may have ankle stiffness that is putting extra load on your Achilles. Work on ankle dorsiflexion exercises (banded ankle mobilisations, calf stretches with the knee bent).
4. Strengthen your foot arch. Simple exercises like short foot, towel curls, and single-leg balance can improve arch function and reduce abnormal loading on the Achilles.
5. Do not ignore your back and hips. If your lower back is stiff or your glutes are weak, your running form will compensate. Hip thrusts, clamshells, and thoracic spine mobility work may be as important for your Achilles as any direct calf exercise.
6. Do not force your feet to point straight ahead. Some natural external rotation is normal and may even be protective. Work with a physiotherapist to determine if your foot rotation is healthy compensation or problematic compensation.
7. Consider a running gait assessment. A good physiotherapist can look at your whole-body running form, identify hidden issues (stiff back, poor hip control, ankle restrictions), and give you specific exercises to address them - not just generic "strengthen your calves" advice.
One key insight from this research
"Higher ankle inversion moment (the force that rolls your foot outward during push-off) reduced Achilles tendinopathy risk by 67%. More external foot rotation was also protective. Foot strike pattern (heel vs forefoot) did not predict injury risk. Each extra 12.5 km per week increased risk by 67%."
Frequently asked questions
Should I change from heel striking to forefoot striking to prevent Achilles problems?
No. This study found no association between foot strike pattern and Achilles injury risk. If you are pain-free with your current pattern, changing it may introduce new injuries (like stress fractures or calf strains) without clear benefit.
How much running is too much?
There is no universal number, but each extra 12.5 km per week increased injury odds by 67%. Be particularly cautious when weekly volume exceeds 40 km, as previous research has shown structural changes in the Achilles tendon at that level. Increase mileage gradually (no more than 10% per week) and take rest days.
My feet turn out when I run. Is that bad?
Not necessarily. This study found that some external rotation was actually protective. The key question is why your feet turn out. If it is due to ankle stiffness or hip tightness, those issues need addressing. If it is your natural anatomy, forcing your feet straight may do more harm than good.
Can lower back problems cause Achilles tendinopathy?
Yes, indirectly. Your body is a chain. A stiff lower back changes how your hips move, which changes how your legs swing, which changes how your foot lands, which changes how your Achilles is loaded. Clinically, I see this pattern frequently. Do not ignore your back and hips when treating Achilles pain.
What is the best exercise to prevent Achilles tendinopathy?
There is no single "best" exercise. Based on the study findings, exercises that improve ankle inversion moment (like resistance band ankle inversions) and foot arch strength are beneficial. However, addressing issues higher up (lower back mobility, hip control, ankle dorsiflexion) may be equally or more important. A thorough assessment by a physiotherapist is the best way to identify your specific weaknesses.
This study is an important step forward in understanding Achilles tendinopathy. It tells us that ankle inversion strength and foot rotation matter, while foot strike pattern does not. It confirms that running volume is a major risk factor.
But as a clinician, I know that research studies cannot capture every variable. In my experience, the runners who struggle with chronic Achilles problems almost always have hidden issues higher up the chain - a stiff lower back, poor hip control, limited ankle mobility. You cannot fix the Achilles by only looking at the Achilles.
If you are a runner dealing with Achilles pain, or if you want to prevent it before it starts, I encourage you to get a thorough assessment. Look at your whole body - not just your ankle. Address the underlying issues, not just the symptoms.
I see runners in Port Macquarie and via telehealth for running gait analysis and injury assessment. If you would like to discuss your specific situation, I am here to help.
- Grant
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Disclaimer: This information is for educational purposes and does not replace individualised medical advice. Always consult a qualified health professional before changing your running technique or training volume. This blog post summarises a published research study (Jandacka D, Skypala J, Plesek J, et al. Biomechanical insights into Achilles tendinopathy risk and protection in runners: a large prospective study. Br J Sports Med. 2026;60:186-197); the original source should be consulted for full methodological details.
