Why does my Achilles hurt when I run?

What it feels like

The classic presentation is stiffness and pain in the tendon for the first ten or twenty steps of the morning, easing as you move, then returning after a run rather than during it. The tendon is often tender to squeeze about two to six centimetres above the heel bone, and may feel thickened compared with the other side.

Pain during the run itself that warms up and disappears is typical and not a reason to stop. Pain that builds through the run, or that is still there the next morning and worse than the day before, means the load was too high.

What is actually happening

Tendinopathy is not inflammation in the way the word tendinitis implies. It is a change in the structure and load tolerance of the tendon, usually because load went up faster than the tissue adapted. A jump in weekly mileage, a switch to hills or speed work, a change in footwear, or a return after time off are the common triggers.

The tendon is not damaged in a way that needs protecting. It is under-prepared for what is being asked of it. That distinction matters, because the treatment is the opposite of rest.

How it is assessed

Assessment covers calf strength and endurance, single-leg hopping and heel raise capacity, ankle range of motion, and how you load the foot during running. Where the presentation is unclear, the pattern of pain across the day and in response to specific loads usually separates tendon pain from the other structures in the area.

At The Runner's Academy this includes treadmill gait analysis, because cadence, stride length and foot strike all change how much the tendon has to absorb.

How it is treated

The foundation is progressive loading: heavy, slow calf work that gradually rebuilds the tendon's capacity, progressed on how the tendon responds over twenty-four hours rather than on how it feels during the exercise. Most programmes run twelve weeks, with running maintained at a reduced volume rather than stopped entirely wherever symptoms allow.

Where symptoms have been present for months and loading alone has stalled, extracorporeal shockwave therapy can be added. Running volume is rebuilt on a structured progression rather than by feel.

What to do first

Stop increasing your training load, keep running at a volume that leaves the tendon no worse the following morning, and start calf loading. If you are already three weeks in and nothing is changing, that is the point to have it assessed rather than to keep waiting.