Achilles tendinopathy is a painful, degenerative condition of the Achilles tendon, the thick band of tissue connecting your calf muscles to your heel bone. Despite what the older term “tendinitis” suggests, this isn’t primarily an inflammatory problem. The tendon itself breaks down at a structural level, with disorganized collagen fibers, new blood vessel growth into tissue that’s normally blood vessel-free, and nerve fiber ingrowth that contributes to persistent pain. Understanding what’s actually happening inside the tendon helps explain why it can be stubborn to treat and why the right rehab approach matters so much.
Why It’s Called Tendinopathy, Not Tendinitis
For decades, a painful Achilles was labeled “tendinitis,” implying that inflammation was the core issue. When researchers examined tissue samples under the microscope, they found something different. The tendon showed degenerative changes: collagen fibers in disarray, increased mucoid (gel-like) substance between fibers, and cell death within the tendon. This led to a shift in terminology, first to “tendinosis” and now more broadly to “tendinopathy,” which simply means tendon disease without assuming a specific mechanism.
This distinction matters because treatments that target inflammation, like ice and anti-inflammatory medications, don’t address the underlying structural breakdown. The condition involves repetitive overloading that outpaces the tendon’s ability to repair itself. Over time, cells in the tendon die off, and the body responds by growing new blood vessels and nerve fibers into the damaged area. Those nerve fibers are a key reason the condition hurts. Meanwhile, the tendon produces enzymes that further break down collagen, creating a cycle of damage that doesn’t resolve on its own without the right stimulus.
Two Types Based on Location
Achilles tendinopathy comes in two forms depending on where the damage occurs, and the distinction affects both prognosis and treatment.
Midportion tendinopathy affects the middle of the tendon, roughly 2 to 7 centimeters above where it attaches to the heel bone. This is the more common type and generally responds better to exercise-based treatment, though about 40% of people still have lingering symptoms after completing a rehab program.
Insertional tendinopathy occurs right where the tendon meets the heel bone, within the bottom 2 centimeters. It tends to be more structurally complex. In one study, 94% of insertional cases had calcifications (hard mineral deposits) within the tendon, compared to 56% of midportion cases. New blood vessel growth was also far more common: 86% versus 38%. These additional structural changes likely explain why insertional tendinopathy is harder to manage with exercise alone, with up to 68% of people continuing to experience symptoms after completing rehab. Despite these structural differences, pain and function scores are similar between the two types, meaning insertional tendinopathy doesn’t necessarily hurt more, it’s just more resistant to standard loading programs.
Risk Factors Beyond Overuse
Sudden increases in training volume or intensity are the classic trigger, especially in runners and athletes who do a lot of jumping. But the story doesn’t end with mechanical load. Several metabolic and systemic factors raise your risk.
Type 2 diabetes is a significant one. Chronically elevated blood sugar damages tendons in multiple ways. It impairs the tiny blood vessels that supply the tendon, increases oxidative stress that breaks down tissue, and causes sugar molecules to bond with collagen fibers, making them stiffer and more brittle. Even people with diabetes who have no tendon pain often show measurable changes on imaging, including thickened, softened Achilles tendons and collagen disorganization at the tendon-bone junction. High cholesterol operates through a similar mechanism, depositing lipids within the tendon substance.
Other well-established risk factors include age (tendon repair slows as you get older), being overweight, wearing unsupportive footwear, and having stiff or weak calf muscles. Certain antibiotics in the fluoroquinolone class are also known to weaken tendons and can trigger or worsen tendinopathy.
What It Feels Like
The hallmark symptom is pain in the back of the heel or lower calf that’s worst when you first get moving. Morning stiffness is extremely common, with the first few steps out of bed feeling tight and sore. The pain typically eases as the tendon warms up, then returns after prolonged activity or the next morning. In more advanced cases, the tendon may be visibly thickened or swollen, and pain starts occurring during activity rather than just before and after.
Activities that load the tendon through a stretch, like walking uphill, climbing stairs, or pushing off during running, tend to provoke symptoms the most. Some people notice a specific tender spot when they squeeze the tendon between their fingers. The condition usually develops gradually over weeks rather than appearing suddenly, which helps distinguish it from an acute tear.
How It’s Diagnosed
A physical exam is usually enough for diagnosis. Your clinician will palpate (press along) the tendon to locate the painful area and may use a few specific tests. When three common clinical tests are combined, including tendon palpation, a painful arc sign, and the Royal London Hospital test, they have a specificity of about 83%, meaning they’re good at ruling out other conditions when results are negative.
Ultrasound imaging can confirm the diagnosis and show tendon thickening, areas of disorganization, and new blood vessel growth. However, imaging results need to be interpreted carefully. Studies of long-distance runners without any symptoms found that roughly 29% of their pain-free Achilles tendons showed signs of tendon degeneration on ultrasound. Blood vessel growth and swelling appeared at similar rates in both painful and pain-free tendons. In other words, what shows up on a scan doesn’t always match what you feel, and a “bad-looking” tendon on imaging isn’t necessarily a painful one.
Loading Is the Primary Treatment
Progressive loading through exercise is the gold standard for Achilles tendinopathy. The goal is to stimulate the tendon to remodel and strengthen, gradually increasing the demands placed on it. Two structured protocols have the most evidence behind them.
The Alfredson protocol, developed in 1998, focuses on eccentric exercises, meaning you lower your heel slowly off the edge of a step, loading the tendon as it lengthens. The original program calls for 3 sets of 15 repetitions with a straight knee, then 3 sets of 15 with a slightly bent knee, performed twice daily, seven days a week, for 12 weeks. That’s 180 repetitions per day, which is a significant commitment. The straight-knee version targets the larger calf muscle (gastrocnemius), while the bent-knee version targets the deeper muscle (soleus).
Heavy slow resistance training is an alternative approach that uses heavier weights with fewer repetitions and a slower tempo, typically performed three times per week rather than daily. Research comparing the two protocols shows similar outcomes, so the choice often comes down to personal preference and which program you’re more likely to stick with consistently.
For insertional tendinopathy, standard heel-drop exercises off a step can sometimes aggravate symptoms because they compress the tendon against the heel bone at the bottom of the movement. Modifications, like performing calf raises from the floor rather than off a step, are often necessary.
Recovery Timeline
Full recovery takes anywhere from six weeks to a year, depending on how irritable the tendon is, the degree of structural change, and the quality of rehabilitation. Most people should expect a timeline measured in months rather than weeks.
For runners aiming to return to their sport, specific benchmarks help gauge readiness. A commonly used set of criteria before starting a return-to-running program includes being able to perform 25 bilateral calf raises at full range of motion with minimal pain, 2 sets of 25 single-leg calf raises, weighted single-leg calf raises at roughly a third of body weight, and completing single-leg pogo jumps for 30 seconds without pain. Meeting these milestones indicates the tendon can handle the repetitive impact forces of running.
Rushing back before these benchmarks are met is one of the most common reasons people relapse. The tendon adapts more slowly than muscles do, so feeling stronger in the calf doesn’t necessarily mean the tendon is ready for high-impact load.
Shockwave Therapy and Other Options
When exercise alone isn’t enough, shockwave therapy is one of the better-supported adjunct treatments for midportion tendinopathy. It delivers acoustic energy pulses into the tendon to stimulate a healing response. A typical course involves three sessions spaced one week apart. In clinical trials, patients treated with shockwave therapy showed significantly improved pain and function scores at six weeks compared to their pre-treatment baseline, and the improvement was greater than with ultrasound therapy alone.
Other options that may be used alongside a loading program include manual therapy, activity modification to reduce tendon irritation in the short term, and orthotic inserts to address biomechanical contributors. Corticosteroid injections are generally discouraged for Achilles tendinopathy because they can further weaken an already compromised tendon. Surgery is reserved for cases that fail to improve after six or more months of well-structured conservative treatment, and outcomes vary.
The single most important factor in recovery is consistent, progressive loading. Tendons need mechanical stimulus to heal, and passive rest alone tends to make the condition worse over time by further weakening the tissue. Starting with a tolerable level of exercise and building gradually gives the tendon the signal it needs to remodel and strengthen.