Achilles pain is one of the most common, and most stubborn, injuries in runners and triathletes. It often starts quietly, gets ignored because it "loosens up" once you're moving, and then lingers for months if it isn't managed properly. Here's what it actually is, why it happens, and how to deal with it.
What Is Achilles Tendinopathy?
Achilles tendinopathy is an overload injury to the Achilles tendon — the thick tendon connecting your calf/soleus muscles to your heel. It happens when the load placed on the tendon exceeds its current capacity to handle it, causing the tendon structure to change and become painful.
It's not inflammation in the traditional sense (despite the old term "Achilles tendinitis"). It's a breakdown in the tendon's ability to tolerate load, which is why rest alone rarely fixes it, the tendon needs to be trained back up, not just left alone.
Two Types of Achilles Tendinopathy
Where the pain shows up matters, because it changes how it's treated.
Mid-portion Achilles tendinopathy
Pain 2–6cm above the heel, in the "belly" of the tendon
The most common type in runners
Often a firm, tender lump or thickening in the tendon
Insertional Achilles tendinopathy
Pain right where the tendon attaches to the heel bone
Often aggravated by stretching (which can actually make this type worse, not better)
More common with a sudden increase in hill running or speed work
Common Signs
Stiffness and pain first thing in the morning, or after periods of rest
Pain that eases as you warm up, then returns after activity or the next morning
A gradual build-up rather than a single incident
Tenderness when pressing directly on the tendon
Pain that worsens with hills, sprinting, or a sudden jump in training volume
Why It Happens
Achilles tendinopathy is almost always a load-management problem. Common triggers include:
A sudden increase in running volume or intensity
Adding hill sessions or speed work too quickly
Increasing training load after time off (a common trap after injury, illness, or a break in a triathlon off-season)
Calf and lower-leg strength that hasn't kept pace with training demands
Footwear changes, particularly a sudden switch to lower-drop or minimalist shoes
For triathletes, the combination of running, cycling, and swimming can also mask early symptoms — the tendon might feel fine in the pool but flare on the run leg, and the accumulated load across all three disciplines can add up faster than expected.
How It's Treated
Tendons respond to appropriate load, not rest. The most effective treatment approach is progressive strength training, gradually increasing the demand on the tendon so it rebuilds capacity rather than staying fragile.
A typical rehab progression includes:
Isometric calf holds to manage pain in the early stages
Progressive heavy, slow resistance training (calf raises with increasing load)
Reintroducing energy-storage exercises like hopping and bounding as capacity improves
A structured return to running, gradually reintroducing pace, hills, and volume
Complete rest often makes things worse in the long run, because the tendon loses capacity and becomes even less prepared for the load of running when you return.
When to See a Physio
Achilles pain that lingers for more than a couple of weeks, or that's affecting your training, is worth getting assessed properly. Getting the diagnosis right, mid-portion versus insertional, and how irritable the tendon currently is, changes the entire treatment approach. The right assessment also identifies why the tendon became overloaded in the first place, whether that's a training error, a strength deficit, or a change in footwear, so the same issue doesn't come back once you're pain-free.
The Bottom Line
Achilles tendinopathy is manageable, but it takes the right approach and early intervention, not just rest, and not just pushing through it. With a proper diagnosis and a progressive loading plan, most runners and triathletes get back to full training without ongoing issues.
Kye Simpson, Senior Physiotherapist at Streamline Physiotherapy, Thirroul.