Achilles tendinopathy: why rest is the wrong instinct

Achilles tendinopathy is pain, stiffness and often thickening in the tendon running from the calf to the heel. It is one of the most common overuse injuries in runners, and it also turns up in people who have not run in years.

The most important thing to understand about it is counter-intuitive: resting a tendon rarely fixes it, and often makes the eventual return harder.

The pattern that identifies it

Stiffness and pain that are worst at the start of activity and after periods of rest, the first steps in the morning, or standing up after sitting through a film. It often warms up during exercise and then aches afterwards, sometimes for hours.

That “warms up then hurts later” pattern is characteristic. Pain that gets steadily worse throughout an activity without ever easing points somewhere else.

Two different problems with the same name

Where the pain sits changes the treatment substantially.

Mid-portion tendinopathy, 2 to 6cm above the heel bone, in the body of the tendon. This is the more common form and the one that responds best to loading programmes.

Insertional tendinopathy, right where the tendon attaches to the heel bone. This one is more stubborn, and one specific thing matters: exercises done into deep dorsiflexion, where the tendon is compressed against the bone, tend to aggravate it. A programme that works well for a mid-portion case can make an insertional one worse.

If you have been given a rehabilitation programme that is not helping, this is the first thing worth checking.

Why it is not tendinitis

The “-itis” implies inflammation. Tissue studies of long-standing Achilles pain show disorganised collagen, increased ground substance and new blood vessel growth, a failed healing response rather than an inflammatory one.

This matters because it explains why anti-inflammatories, ice and rest deliver short-term comfort and no lasting change. The tendon has failed to adapt to the load being put through it, and the only thing that reliably drives adaptation is load itself, applied in the right dose.

What causes it

Almost always a change rather than an absolute amount:

• A sudden increase in running volume, intensity or hills
• Returning to activity after time off at the level you left at
• New footwear, particularly a change in heel drop
• Reduced calf strength or ankle flexibility
• Age, the tendon’s capacity to adapt slows from the forties onward
• Certain antibiotics, particularly fluoroquinolones, which carry a known tendon risk

The treatment that works

Progressive loading. The core of it, and there is good evidence behind it. Heavy slow resistance calf work, or an eccentric-focused programme, performed consistently over months. Not weeks, months.

Two things people get wrong. The first is stopping when it starts feeling better, which is usually at about the point the tendon is starting to adapt. The second is expecting the exercises to be painless: a moderate, tolerable level of pain during loading is acceptable and does not indicate damage, as long as it settles within 24 hours.

Load management, not rest. Reduce running to a level the tendon tolerates rather than stopping entirely. A tendon that has been fully rested for six weeks has lost capacity, and returning to the same running that caused the problem now meets a weaker tendon.

Adjusting the aggravators. A temporary heel raise reduces the load on the tendon and is genuinely useful in insertional cases. Reducing hill work and speed sessions while capacity rebuilds. Checking that new shoes are not the cause.

Shockwave therapy. For cases that have not responded to several months of loading, extracorporeal shockwave therapy has reasonable evidence in chronic Achilles tendinopathy, and it is available at the clinic. It works alongside a loading programme, not instead of one.

How long it takes

Three to six months for a well-established case, sometimes longer. Improvement is measured over weeks rather than days, and the honest version of the timeline is worth having up front, most of the people who abandon a loading programme do so at around week four, which is before it has had time to work.

When it is something else

Two things need excluding:

A partial or complete tear. A sudden sharp pain, often described as being kicked in the back of the leg, sometimes with an audible snap, followed by difficulty pushing off. A complete rupture needs urgent assessment, same day, not next week.

Referred or alternative causes. Retrocalcaneal bursitis, Haglund’s deformity, a posterior ankle impingement or plantaris involvement can all produce pain in the same region. If a well-executed loading programme is doing nothing at all after a couple of months, revisiting the diagnosis is more useful than persisting with it.