Achilles tendinopathy is the running injury that hides in plain sight. Morning stiffness in the back of the lower leg. A dull ache that warms up and disappears mid-run, then returns the next morning worse. The 2019 BJSM Achilles tendinopathy consensus statement places lifetime incidence in long-distance runners at around 50 percent. Half of us will get it at some point. The honest question is not whether to worry, but how to identify it early and act before it becomes chronic.
This article is the diagnostic primer. It is not treatment. The aim is to give the recreational Indian runner the clinical vocabulary, the differential framework, and the load-history thinking that will help you decide whether what you have is Achilles tendinopathy, and what to do about a referral if it is.
The anatomy and the pathology, in clinical terms
The Achilles tendon is the largest tendon in the body. It transmits force from the calf complex, made up of the gastrocnemius and soleus, to the calcaneus. Under repeated running load, the tendon adapts. When the load exceeds the tendon's adaptive capacity, the structure begins to fail. The result is what we currently call tendinopathy, which has replaced the older term tendinitis in the clinical literature because the histology shows minimal inflammation and significant disorganised collagen.
The research shows the tendinopathic Achilles has thickened collagen fibres, increased ground substance, and neovascularisation in chronic cases. The pain is mechanical, load-related, and typically localised. Two anatomical subtypes matter clinically: mid-portion tendinopathy, which sits two to six centimetres above the calcaneal insertion, and insertional tendinopathy, which sits at or just above the insertion. The two have different histories and different load responses.
Mid-portion versus insertional, in plain terms
Mid-portion tendinopathy is the more common type in distance runners. Pain is two to six centimetres up the tendon from the heel. It responds well to eccentric loading protocols. Insertional tendinopathy sits at the bony attachment, can be associated with Haglund deformity or a prominent calcaneal bony bump, and is more sensitive to deep dorsiflexion. The clinical differentiation matters because the rehabilitation differs.
What it is not
Achilles tendinopathy is not tendinitis. The histological evidence has been clear since the early 2000s. It is not a partial tear unless trauma was involved. It is not always Haglund's. And it is not always insertional, even when it feels low. A careful physical examination by a clinician with running experience is the differentiation, not self-diagnosis on imaging.
The causes: what the evidence supports
Achilles tendinopathy is multifactorial. The risk factors with the strongest evidence are training-load related. A 2017 systematic review in the British Journal of Sports Medicine identified rapid increases in running volume, intensity, and hill running as the most consistent training-related risk factors. The body's tendons adapt slowly, on a timescale of weeks to months. The training programme that adapts faster than the tendon is the training programme that breaks it.
Intrinsic risk factors with consistent evidence include reduced ankle dorsiflexion range, calf strength asymmetry, and prior Achilles or calf injury. Age and sex matter too: incidence rises with age, and men are over-represented in chronic cases. The 2019 BJSM consensus paper synthesises these intrinsic factors but acknowledges that the training-load variables are more modifiable, and therefore more useful, in prevention conversations.
The training-load story
Most cases I see in Indian runners trace back to one of three load patterns. A sudden bump in weekly volume, often after registering for a half or full marathon. A new training stimulus, like switching to hill repeats or speedwork after a flat-volume base. A return to running after a layoff, with the runner trying to pick up where they left off rather than rebuilding from below.
The acute-to-chronic workload ratio framework, originally developed in team sports and now widely cited in running research, helps quantify the risk. Acute weekly load divided by the four-week rolling average gives a ratio. Values above 1.3 to 1.5 are associated with elevated injury risk in observational studies. The principle, more than the exact ratio, is what matters.
The footwear and surface conversation
Sudden changes in footwear or surface are a known trigger. A switch from a higher-drop trainer to a low-drop or zero-drop shoe shifts load onto the Achilles. Adding hill repeats to a flat base increases dorsiflexion-and-load combinations. Both should be introduced over four to six weeks, not in a single training week.
The clinical diagnosis
Achilles tendinopathy is a clinical diagnosis. Imaging is rarely needed for first-line cases. The diagnostic features are consistent across the literature: localised pain in the tendon, morning stiffness that warms up with activity, pain on palpation, and pain on tendon-loading tests like heel raises or hopping.
The history that points to tendinopathy
A typical history sounds like this. The runner notices stiffness in the back of the lower leg in the morning. The first few steps out of bed are painful. The stiffness eases within a few minutes. Running starts uncomfortable, warms up, becomes painful again in the cool-down or the next morning. There is usually a load-history clue in the preceding two to six weeks: a volume jump, a new workout type, a new shoe, or a return from time off.
The physical examination findings
The clinician palpates the tendon and identifies the pain location, mid-portion or insertional. Pain on resisted plantarflexion. Pain on single-leg heel raises, particularly in repetitions. Pain on hopping. The Royal London Hospital test for mid-portion tendinopathy, where pain reduces with the tendon tensioned in dorsiflexion, has reasonable sensitivity in chronic cases. A clinician with running experience can usually make the diagnosis in a single consult.
When imaging matters
Ultrasound and MRI are used when the diagnosis is uncertain or when conservative management has failed. Imaging findings include tendon thickening, hypoechoic regions on ultrasound, and increased signal on MRI. The catch: imaging findings correlate poorly with symptoms. Many asymptomatic runners have abnormal imaging. The clinical picture leads. The image follows.
For Indian runners, imaging is also a cost question. An ultrasound in a metro city typically runs four to six thousand rupees, an MRI several times that. Reserve imaging for cases where the diagnosis is unclear, where there is concern about partial rupture, or where the response to a structured loading programme has been poor over twelve weeks.
The differential diagnosis
Achilles pain is not always Achilles tendinopathy. The differential includes retrocalcaneal bursitis, Haglund deformity, posterior ankle impingement, sural nerve irritation, and partial Achilles tear. The clinical examination, supported by imaging when needed, separates them. The history of trauma is important. A sudden pop or sharp pain mid-run, with reduced push-off strength, is a red flag for partial or full rupture and warrants urgent assessment.
The acute Achilles rupture
Acute Achilles rupture is a different beast. The history is sudden, often felt as a kick to the back of the leg. The Thompson test, where squeezing the calf fails to produce plantarflexion, has high sensitivity. A suspected rupture is a same-day clinical assessment, not a wait-and-see.
What to do next
If your history and symptoms match the tendinopathy pattern, the next step is a structured loading programme. The 2019 BJSM consensus supports progressive tendon loading, beginning with isometric calf holds, advancing to heavy slow resistance or eccentric loading. The programme is detailed in our exercises library and the broader rehabilitation framework lives in our recovery guide.
For the wider injury context, the injuries hub covers the full Indian-runner injury landscape, including the related calf and lower-leg conditions that mimic Achilles symptoms. If your training load was the trigger, the STRIDD plan generator will help you rebuild a load curve that respects tendon-adaptation timescales. Browse the rest of the Running Lab for the complete library.