Published 7 June 2026 · 14 min read · UK runners
TL;DR
- Achilles tendonitis is pain and stiffness in the Achilles tendon, classically worse in the morning's first steps and at the start of runs.
- The Alfredson protocol (eccentric calf raises 3x15 reps twice daily) has the strongest research evidence. It takes 12 weeks. It works.
- Edge builds general strength and mobility into every plan. The Achilles-specific eccentric calf protocol in this article you do yourself or with a physio.
By the numbers
What is Achilles tendonitis (and why it's actually "tendinopathy")
The Achilles is the thick rope of tissue running from the back of your calf down to your heel bone. It is the largest tendon in your body, and in runners it does a huge amount of work, taking around eight times your body weight on every single stride.
When that tendon gets overloaded faster than it can recover, it gets sore. In the early days clinicians called this "tendonitis", which means "tendon inflammation". The "itis" suffix is what most runners search for, so we use it in the title of this guide.
The truth is more subtle. Modern research shows that when the pain has been around for more than a few weeks, there is very little classic inflammation in the tendon. What you actually have is a disorganised, thickened tendon with tiny areas of damage. The proper name for this is "tendinopathy" or "tendinosis".
This matters because the treatments are different. Anti-inflammatories and steroid injections target inflammation, and they do not fix the underlying tendon. Loading the tendon in the right way does. That is why this article is built around progressive strength work, not rest and ice.
How to know you have it: 5 classic signs
Achilles tendonitis has a very recognisable pattern. If you tick three or more of these, the picture is fairly clear.
- Morning stiffness in the tendon. The first few steps out of bed feel sore and stiff in the back of the heel. It eases within a few minutes of walking.
- Pain at the start of a run. The tendon hurts in the first 5 to 10 minutes, then often warms up and feels almost normal mid-run.
- Pain returns later or the next day. Soreness comes back as you cool down, and the next morning's stiffness is worse.
- Visible swelling or thickening of the tendon. Run your finger and thumb up the tendon. If one side feels noticeably fatter than the other, that is the tendon thickening.
- Sore on palpation. Pinching the tendon between finger and thumb is tender. It should not be.
Insertional vs mid-portion: an important distinction
Not all Achilles pain is the same, and the location changes the treatment.
Mid-portion Achilles tendinopathy is pain in the middle of the tendon, around 2 to 6cm above the heel bone. This is the more common type. It responds very well to the classic Alfredson eccentric protocol below, performed off a step so the heel can drop below the level of the toes.
Insertional Achilles tendinopathy is pain right at the back of the heel, where the tendon attaches to the bone. This is the version that older runners and runners who have suddenly switched to zero-drop shoes get more often. Dropping the heel below the step compresses the painful spot and tends to flare it up. For this version you do the eccentric raises on flat ground only, and a small heel lift in the shoe usually helps.
If you cannot tell which you have, treat as insertional. It is the safer default.
The real causes: 5 things that bring it on
1. A sudden mileage jump
The single biggest cause. Tendons adapt more slowly than muscles and lungs. If you jump from 15 miles a week to 25 miles a week because you have signed up for a half marathon, the calf can handle it but the tendon often cannot. The classic 10% per week rule exists for this reason.
2. Weak or tight calves
The calf and the Achilles work as one unit. Weak calves force the tendon to do more work than it should. Tight calves keep the tendon under constant tension, even at rest. Most runners with Achilles pain have one or both.
3. Hill training overload
Uphill running loads the Achilles through a longer range. Downhill running loads it eccentrically, which is the most damaging type of contraction when the tendon is already irritated. A sudden block of hill repeats is a very common trigger.
4. A footwear change
Moving from a cushioned shoe with a 10mm heel drop to a 4mm or zero-drop shoe lengthens the tendon on every step. The calf and tendon need months to adapt. Doing it in a week is one of the most predictable ways to trigger Achilles pain. The same goes for switching out of carbon plate racers back into flat trainers.
5. Age 40 and over
Tendons lose water content and elasticity as we age. From the early 40s onwards the Achilles becomes more sensitive to load spikes and slower to recover. This is not a reason to stop running. It is a reason to be more patient with build-ups and more consistent with strength work.
The Alfredson eccentric protocol (gold standard)
This is the single most evidence-backed treatment for mid-portion Achilles tendinopathy. It was developed by Swedish researcher Hakan Alfredson in the 1990s, and the success rate in the original study was around 90%.
It is deceptively simple, and most runners get it wrong by doing too few reps, stopping too early, or quitting because it gets sore. The protocol is meant to feel uncomfortable. That is the loading working.
The protocol
- The move: Stand on the edge of a step on the affected leg. Push up onto your toes using the good leg, then shift weight onto the bad leg and slowly lower the heel below the level of the step over a count of 3 seconds. Use the good leg to come back up.
- Two variations: Do half the sets with the knee straight, half with the knee slightly bent. This loads both heads of the calf.
- The dose: 3 sets of 15 reps, knee straight. Then 3 sets of 15 reps, knee bent. Twice a day. Every day.
- The duration: 12 weeks. Not 2 weeks. Not 4 weeks. 12.
- The progression: Once you can do all 90 reps a day pain-free, add weight in a backpack. Keep adding weight every week or two.
Insertional cases: Do this on flat ground, do not drop the heel below toe level.
It is normal for the tendon to feel sore during and after these. A pain level of 3 or 4 out of 10 during the exercise is fine and even expected. If pain is climbing above 5 out of 10, or is worse the next morning, drop the weight or the reps for a week.
7 supporting exercises
The Alfredson protocol is the main course. These are the side dishes. Two or three sessions a week is plenty.
- Standing calf stretch. Hands on a wall, back leg straight, heel down, hold 30 seconds. Two rounds each side. Skip if you have insertional Achilles pain.
- Plantar fascia stretch. Sitting, pull your toes up towards your shin and hold 30 seconds. The plantar fascia and Achilles share connective tissue, so this often helps.
- Glute bridges. 3 sets of 12. Strong glutes mean the calf does less of the propulsion work on every stride.
- Single-leg balance. 30 seconds each leg, eyes closed if you can. Restores the small stabilising muscles around the ankle.
- Calf foam rolling. 60 seconds each calf, slow passes. Reduces tone in the calf and offloads the tendon.
- Toe walks (insertional cases). 20 metres on the balls of your feet. A useful early load for the insertional version.
- Step-up calf raise. Once you are pain-free, this is your maintenance move. 3 sets of 12 each leg, twice a week, for life.
Your Achilles tendonitis risk: a quick check
Tick every statement that is true for you in the last 4 weeks:
- My weekly mileage has gone up by more than 20% in the last month.
- I have added hill repeats or hilly long runs in the last 4 weeks.
- I have changed shoes (especially to a lower drop) in the last 6 weeks.
- I am over 40.
- I do no calf strength work, ever.
- My calves feel tight most mornings.
0-1 ticks: Low risk. Keep doing what you are doing. 2-3 ticks: Moderate risk. Add the 7 supporting exercises twice a week. 4+ ticks: High risk. Start the maintenance step-up calf raise now, slow any mileage build to 5% per week, and read the prevention section twice.
What NOT to do
- Do not stretch aggressively if you have insertional pain. Pulling the heel down compresses the painful insertion. It feels productive. It is not.
- Do not get a corticosteroid injection into the tendon. Steroid weakens collagen and there is a real risk of rupture. Most UK NHS sports physios will refuse to do this for Achilles. There is a reason.
- Do not ignore morning stiffness. It is the tendon's most honest signal. If morning stiffness is getting worse week to week, your current training is too much for the tendon to recover from.
- Do not "run it off". Achilles pain that warms up mid-run does not mean it is healing. The tendon is still under the same load. You are just getting better at not noticing.
- Do not foam roll the tendon itself. Foam roll the calf. The tendon is not a muscle and aggressive rolling can flare it up.
Return to running protocol
You can return when:
- You have zero morning stiffness for at least 7 days in a row.
- You can hop on the affected leg 10 times pain-free.
- You can do single-leg calf raises pain-free with body weight.
Once you tick all three, build back like this:
- Week 1: 1 mile, easy pace, every other day. 3 runs total.
- Week 2: 1.5 miles, every other day. 3 runs.
- Week 3: 2 miles, every other day. 3 runs.
- Week 4 onwards: add roughly 1 mile every 7 to 10 days, keep it flat, keep it easy.
- Do not add hills or speed work until you are back at your previous easy mileage and pain-free for 2 full weeks.
Keep doing the Alfredson protocol the whole way through. Do not stop just because you are running again.
When to see a physio or doctor
This is general information, not medical advice. Please see a qualified clinician if any of the following apply:
- Pain has not improved at all after 6 weeks of consistent eccentric loading.
- The tendon is visibly swollen or warm.
- You felt a sudden snap, pop, or kick in the back of the heel during activity, especially if you cannot push off the foot afterwards. This can indicate a rupture and is an A&E visit.
- You have pain at rest, at night, or pain that is steadily getting worse rather than better.
- You have any numbness, tingling, or weakness in the foot.
A good sports physio will confirm the diagnosis, check whether your case is insertional or mid-portion, and progress your loading more aggressively than you would on your own. If you are 6 weeks in and stuck, that visit is the best money you will spend.
How Edge fits in
Edge builds general strength and mobility into every plan. The Alfredson eccentric protocol and Achilles-specific exercises in this article you do yourself, or work on with a physio. Edge has coach video demos for the general strength and mobility moves in your plan, not for Achilles rehab specifically.
What Edge does help with is the part that prevents Achilles tendonitis in the first place: a sensible adaptive starting plan that does not jump your mileage, general calf and glute strength built into every week, and Flexi Swap so when life moves a long run you can shift it without doubling up two hard days back to back. There are 17,000+ UK members training this way.
If you are coming back from Achilles tendonitis, build your weekly running schedule in Edge, do the Alfredson protocol on top, and use the in-app voice prompts on easy runs to keep effort honest.
Making fitness feel good for everyone. Free 7-day trial, then £19.99 a month or £119.99 a year.
Frequently asked questions
What is Achilles tendonitis?
Achilles tendonitis is pain, stiffness, and often thickening of the Achilles tendon, the thick band that runs from the calf to the heel bone. In runners it is usually caused by overloading the tendon faster than it can recover. When it has been around for more than a few weeks it is more accurately called Achilles tendinopathy, because the issue is tendon degeneration rather than classic inflammation.
How long does Achilles tendonitis take to heal?
For most runners, 6 to 12 weeks of consistent eccentric loading with the Alfredson protocol. Insertional cases can take longer, often 12 to 16 weeks. Chronic cases that have been ignored for a year or more can take 4 to 6 months. The tendon heals slowly because it has a poor blood supply. Patience is part of the treatment.
Can you keep running with Achilles tendonitis?
Sometimes, but only if pain stays at or below 3 out of 10 during the run, settles within 24 hours, and morning stiffness is not getting worse week to week. If any of those three rules break, you need to stop running and load the tendon with eccentric raises only for 2 to 4 weeks before retrying.
What is the best exercise for Achilles tendonitis?
The Alfredson eccentric heel drop. 3 sets of 15 with the knee straight, then 3 sets of 15 with the knee slightly bent, twice a day, for 12 weeks. Done off a step for mid-portion pain, on flat ground for insertional pain. Research success rate is around 90%.
Should I stretch my Achilles when it hurts?
Gentle calf stretching is fine for mid-portion Achilles pain. For insertional Achilles pain, aggressive stretching that pulls the heel below the toes compresses the painful insertion and tends to make it worse. If you do not know which you have, do not stretch into pain. The eccentric heel drops are doing the lengthening work you need.
When should I see a doctor about Achilles pain?
See a clinician if pain has not improved after 6 weeks of consistent eccentric loading, if the tendon is visibly swollen or warm, if pain is at rest or at night, or if pain is getting worse rather than better. Go to A&E immediately if you felt a sudden snap or kick in the back of the heel and cannot push off the foot, as this can indicate a tendon rupture.
