Achilles tendinopathy is a chronic, painful condition of the Achilles tendon, the thick band of tissue connecting your calf muscles to your heel bone. It develops when the tendon undergoes structural breakdown faster than your body can repair it, leading to pain, stiffness, and reduced function. Unlike a sudden tear or rupture, tendinopathy is a gradual process that typically worsens over weeks or months.
What Happens Inside the Tendon
A healthy Achilles tendon is remarkably strong. About 95% of its collagen is type I, arranged in neat, parallel fibers designed to handle enormous loads. In tendinopathy, that organized structure breaks down. The collagen fibers become disorganized and fragmented, and the tendon starts producing more type III collagen, a variety that forms smaller, less organized fibers with reduced mechanical strength. Think of it as replacing steel cables with rubber bands.
Alongside this collagen shift, the tendon develops an increase in blood vessel growth (neovascularization) and an accumulation of water-attracting molecules in the tissue. These changes make the tendon thicker and softer, but not stronger. On MRI, a tendinopathic Achilles tendon averages about 11 mm thick compared to roughly 5 mm in a healthy tendon. The tendon also becomes wider and longer overall. Importantly, this is not an inflammatory condition in the traditional sense. The term “tendinitis” (implying active inflammation) has largely been replaced by “tendinopathy” because the tissue changes are primarily degenerative rather than inflammatory.
Where It Occurs
Achilles tendinopathy is generally described in two locations. Midportion tendinopathy affects the middle section of the tendon, typically 2 to 6 centimeters above the heel bone. Insertional tendinopathy occurs right where the tendon attaches to the heel. Midportion tendinopathy is more common, especially in runners and active adults. Insertional tendinopathy can also affect less active people and is sometimes associated with a bony prominence on the heel.
While clinicians have traditionally treated these as distinct conditions requiring different approaches, recent research has questioned whether the differences are clinically meaningful. Risk factors vary somewhat between the two subtypes, but outcomes and management overlap considerably.
What It Feels Like
The hallmark of Achilles tendinopathy is pain at the back of the lower leg or just above the heel. It usually starts as a mild ache after running, jumping, or other activity. Over time, the pain can become more intense, progressing to a burning sensation during longer runs, stair climbing, or sprinting.
Morning stiffness is one of the most recognizable features. You may notice that your first steps out of bed feel stiff and uncomfortable, then gradually loosen up with gentle movement. This “warm-up effect” is characteristic: the tendon feels worst after rest, improves with light activity, and then worsens again with prolonged or intense loading. In advanced cases, pain can persist even at rest, and the tendon may feel noticeably thickened or tender to the touch.
Risk Factors
Training errors are the most common trigger. A sudden jump in running mileage, intensity, or hill work places more load on the tendon than it can adapt to. Switching to minimalist shoes or adding speed work without gradual progression are classic examples.
Several other factors raise your risk:
- Age. Tendon cells deteriorate over time, making middle-aged and older adults more vulnerable.
- Body weight. Higher BMI increases the mechanical load on the tendon with every step.
- Medications. Fluoroquinolone antibiotics (such as ciprofloxacin) are well-established culprits. Tendinopathy can occur at any dose and through any route of administration. The risk increases further if you’re taking more than one medication known to affect tendons, or if you have an autoimmune condition or kidney disease.
- Biomechanics. Reduced ankle flexibility, weak calf muscles, and certain foot postures can alter how force is distributed through the tendon.
How It’s Diagnosed
Diagnosis is primarily clinical, meaning a practitioner can usually identify it through your symptoms and a physical exam. Two specific tests are commonly used. The Royal London Hospital test involves a clinician pressing on the tender spot of your tendon, then asking you to flex your foot upward. If the tenderness significantly decreases or disappears when your foot is flexed, the test is positive. The Painful Arc sign checks whether a swollen area on the tendon moves up and down as you point and flex your foot, confirming the swelling is within the tendon itself rather than in surrounding tissue.
You may also be asked to perform single-leg heel raises or small hops to see whether loading the tendon reproduces your pain. Imaging is not always necessary for diagnosis, but ultrasound or MRI can confirm structural changes and rule out other conditions like a partial tear. On imaging, clinicians look for tendon thickening, areas of abnormal signal within the tendon, and increased blood vessel growth.
Treatment Through Loading
The cornerstone of Achilles tendinopathy treatment is a structured exercise program that progressively loads the tendon. The most well-known protocol, developed by researcher Håkan Alfredson, involves eccentric heel drops: you rise onto your toes using both legs, then slowly lower yourself on the affected leg only, letting your heel drop below the level of a step. The original program calls for 180 repetitions per day (three sets of 15, twice, on both a straight and a bent knee) for 12 weeks.
This is demanding and time-consuming, but it works by stimulating the tendon to remodel its collagen and gradually restore its load-bearing capacity. Some discomfort during the exercises is expected and even considered acceptable, but sharp or worsening pain is a sign to modify the program. Many clinicians now use modified versions of this protocol or combine eccentric work with heavier, slower loading exercises depending on how your tendon responds. The key principle remains the same: tendons adapt to load, so progressively challenging them is essential for recovery.
When Exercise Alone Isn’t Enough
For people who don’t improve sufficiently with exercise alone, shockwave therapy is one of the most studied add-on treatments. This involves directing focused pressure waves at the affected tendon, typically over three sessions spread across several weeks. Research comparing shockwave therapy to eccentric exercise has found both approaches produce similar improvements when used independently. However, combining shockwave therapy with an eccentric exercise program produces significantly better outcomes than exercise alone. This makes it a useful option when a structured loading program has plateaued.
Other treatments that may be offered include ultrasound-guided procedures to target the new blood vessels that develop in the tendon. These approaches aim to reduce pain by disrupting the nerve supply that accompanies abnormal blood vessel growth. Early evidence suggests outcomes comparable to surgery, with a quicker return to activity. After any procedural treatment, you can expect to spend a few weeks in a walking boot, followed by 12 to 16 weeks of guided rehabilitation.
Recovery Expectations
Achilles tendinopathy is not a quick fix. Most people need a minimum of 12 weeks of consistent loading exercises before seeing meaningful improvement, and full recovery often takes three to six months or longer. A five-year follow-up study of patients using the Alfredson heel-drop protocol found that while many improved substantially, the process required patience and consistency.
The biggest mistake people make is stopping their exercise program too early because pain has improved. Tendons remodel slowly, and the structural changes that caused the problem take much longer to resolve than the symptoms. Returning to high-level sport or intense activity before the tendon has rebuilt sufficient strength significantly raises the risk of recurrence. A gradual, staged return to activity, guided by how the tendon responds to increasing load rather than by a calendar date, gives you the best chance of staying pain-free long term.