Achilles tendinitis: the load-and-rebuild approach

The quick answer

An irritated Achilles rarely gets better by resting it and waiting. Tendons adapt to load, and they lose tolerance when you take load away. The treatment with the strongest evidence is the opposite of rest: a progressive calf-loading programme that rebuilds the tendon's capacity, run over weeks to months. ^[1,2,3]

It starts as a stiffness in the back of your heel for the first few minutes of a run, or the first few steps out of bed. You warm up, it fades, you forget about it. Then it stops fading. The tendon feels thick and tender to pinch, and the morning stiffness lasts longer.

That's the classic presentation of midportion Achilles tendinopathy, the load-related tendon problem that the old name "tendinitis" describes poorly, because it isn't mainly an inflammatory condition. ^[5]

What's actually going on

For years the assumption was that an irritated tendon is inflamed, so the fix is rest and anti-inflammatories. The current model is different. Tendinopathy is better understood as the tendon's response to load that outpaced its capacity to adapt, a continuum from a reactive, irritable state toward longer-term changes in the tendon's structure if the overload continues. ^[5]

The practical consequence is large: if the problem is a capacity-versus-load mismatch, then resting (which lowers capacity further) sets you up to fail the moment you run again. The tendon needs to be made more tolerant, and tendons get more tolerant by being loaded. ^[1,2]

Why loading beats rest

This is the best-supported part of Achilles rehab. Eccentric and heavy-load calf programmes have been studied for over two decades. The original heavy-load eccentric protocol produced good outcomes in chronic cases that had not responded to rest. ^[3] Later work showed that progressive loading, whether eccentric, heavy-slow, or a combination, reliably improves pain and function across studies, even if no single protocol is clearly superior. ^[1,2]

A systematic review and meta-analysis of loading protocols found that pain and function improve steadily over a loading programme, but the timeline is measured in weeks to months, not days. ^[2] That's the part runners hate and need to hear: this is a slow rebuild, and the people who recover are the ones who keep loading consistently rather than chasing a quick fix.

You don't have to stop running entirely

One of the most useful findings for runners: you can often keep running through Achilles rehab, as long as you keep the pain within acceptable limits. A pain-monitoring model, where you allow some tendon pain during and after activity but track that it settles and doesn't escalate day to day, produced outcomes as good as complete rest from running, without the detraining. ^[4]

The rule of thumb that comes out of that work: pain during the run is acceptable if it stays low and is back to baseline the next morning. If it climbs run to run, the load is too high and needs to come down. ^[4]

How the loading actually looks

There's no single magic protocol, but the principles are consistent: ^[1,2]

• Load the calf and tendon progressively. Straight-knee and bent-knee calf raises load the two main calf muscles; both matter.
• Make it heavy enough to be challenging, and add load over time as it gets easier.
• Expect a multi-week to multi-month commitment, not a one-week fix.
• Keep it consistent. Sporadic loading doesn't build tendon capacity.

A physio can tailor sets, loads and tempo to where your tendon sits on the irritability spectrum, which is exactly where clinical reasoning earns its keep.

What about the passive stuff?

Heel lifts, massage, anti-inflammatories and the like can take the edge off symptoms, but they don't appear to resolve the underlying capacity problem on their own, and the consensus has moved away from treating inflammation as the main target. ^[5,6] Use them, if you like, as comfort measures around the actual work, not as the work.

Returning to running

If you stopped, the return mirrors the shin-splints principle: start at a load that stays comfortable during the run and doesn't leave the tendon clearly worse the next morning, keep the early conditions consistent, and progress one variable at a time. The tendon-loading work continues alongside the running, not instead of it. ^[2,4]

A sharp, sudden Achilles pain with a pop or a sense of giving way is a different story, possible rupture, and needs urgent assessment, not a loading plan. ^[6]

The takeaway

• Achilles tendinopathy is a load problem, not mainly an inflammation problem. ^[5]
• Progressive calf loading is the treatment with the best evidence, eccentric or heavy-slow, done consistently over weeks to months. ^[1,2,3]
• You can usually keep running, guided by a pain-monitoring rule: low pain that settles by the next day is fine; escalating pain is not. ^[4]
• Passive treatments are comfort, not cure. ^[5,6]

Tendons reward patience and punish shortcuts. Load it, give it time, and it gets stronger than it was. :)

How's it going for you?

Have you rehabbed an Achilles back to full running? What loading worked, and how long did it really take? Share it in the community chat, and if you're in the thick of it, come do an easy Sunday social run with us while you rebuild. :)