What causes Achilles tendinopathy, and why does loading beat rest?

Achilles tendinopathy is one of the most common lower-limb overuse problems we see, and one of the most treatable when it is managed properly. The tendon at the back of your heel has been overloaded, is irritated and has changed structurally, but it is almost always intact. The single most effective treatment is a graded, progressive loading programme built around slow, heavy calf work, guided by a physiotherapist and continued for months rather than weeks. Rest, stretching and anti-inflammatories on their own do not fix it.

What is Achilles tendinopathy?

Achilles tendinopathy is the modern term for a painful, overused Achilles tendon. Older labels like tendonitis or tendinosis are less accurate: the main problem is structural change under load, with only a small inflammatory component and no straightforward tear. The tendon has been asked to do more than it was ready for, and its collagen structure has responded by remodelling in a disorganised way. That is what causes the pain, the morning stiffness and the loss of spring.

There are two main forms, and the distinction matters for treatment. Mid-portion tendinopathy sits 2 to 6 cm above the heel bone, is the more common of the two, and responds well to full-range calf loading. Insertional tendinopathy sits right where the tendon attaches to the heel, is often aggravated by deep dorsiflexion, and needs a more careful early range.

Why does it happen?

Almost always, this is a training-load story. Volume has gone up too quickly, or a new element has been added, or recovery has been squeezed. Common triggers include starting a new running block, ramping mileage before an event, adding hill or speed sessions, changing footwear, or returning to sport after time off. Age, calf strength, ankle mobility and general health also matter, but the trigger is usually the way load has been applied.

How is it diagnosed?

Achilles tendinopathy is a clinical diagnosis. A physiotherapist will take a careful history, look at how the tendon responds to load in the room, and rule out the other things that can mimic it, from a partial tear to a plantaris problem, a posterior ankle impingement or referred pain from the low back. Imaging is not routine. A diagnostic ultrasound scan is useful when the picture is unclear, when a partial tear is suspected, or when a well-run rehab programme is not moving as expected.

How is it treated?

The evidence is consistent and has been for more than two decades. The most effective treatment is a structured, progressive loading programme, built around calf-focused strength work performed slowly and heavily, three or four times a week, and continued for at least 12 weeks. The original eccentric protocol described by Alfredson is still widely used, and more recent work on heavy slow resistance has shown similar or better outcomes with a schedule most people find easier to stick to.

Around that, we do several things at once. We modify running or sport rather than removing it, so the tendon keeps working without being flared. We monitor pain during, after and the next morning, and use that to adjust load. We look at the rest of the chain, calf and hip strength, ankle range, footwear, running form, and address what actually matters. Shockwave therapy has a role in more stubborn cases and works best used alongside loading. Injections into the tendon are avoided. Surgery is a last resort, for the small minority who have not responded to a fair trial of rehab.

What does recovery look like?

Progress is rarely linear. Most people notice meaningful change in symptoms and morning stiffness within 8 to 12 weeks, a return to steady running or sport within 3 to 6 months, and a genuine sense that the tendon is robust again after that. Flare-ups during the process are normal and usually mean the next progression came slightly too soon, not that the programme is failing.

When should you see a physiotherapist?

The best moment to see a physiotherapist is early. Pain that has been there for more than a couple of weeks, morning stiffness, or a tendon that flares whenever you push volume all deserve a proper assessment before they settle in. Our physiotherapy team in Milton Keynes will diagnose what is going on, build a loading programme that is right for the stage you are at, and progress it as the tendon responds. You can also read our companion piece on plantar fasciitis if your pain is in the sole rather than the tendon, or see how physiotherapy at Hanbury Health works. For treatment in Milton Keynes, see our tendon pain physiotherapy page.