What Is Achilles Tendinitis? Symptoms & Treatment

Achilles tendinitis is a painful condition of the Achilles tendon, the thick band of tissue connecting your calf muscles to your heel bone. It typically develops when the tendon is subjected to more load than it can handle, whether from a sudden spike in running mileage, years of repetitive stress, or something as seemingly minor as a change in footwear. Despite the name ending in “-itis,” which implies inflammation, most chronic cases actually involve something different under the microscope, and that distinction shapes how the condition should be treated.

What the Achilles Tendon Actually Does

Your Achilles tendon is the strongest tendon in the body, and it does far more than simply anchor your calf to your foot. It acts as a spring and shock absorber during walking and running, storing elastic energy with each step and releasing it to propel you forward. This energy-recycling mechanism lets your calf muscles work over smaller ranges and at slower speeds than they would otherwise need to, which is a big part of why humans are efficient distance walkers and runners.¹ The tendon is not a single uniform cable, either. It consists of distinct fascicle bundles that arise from the different muscles of the calf, and these bundles slide past each other and stretch by different amounts during movement. During walking, the outer part of the tendon stretches roughly 16 to 29 percent more than the deeper part, and this difference becomes more pronounced at faster speeds.² That internal sliding and differential loading may help explain why the tendon is so vulnerable to overuse injuries: some regions absorb more stress than others, and those areas can break down first.

Tendinitis, Tendinosis, Tendinopathy: Why the Words Matter

If you have had Achilles pain for more than a few weeks, the term “tendinitis” is probably a misnomer. When researchers examine chronically symptomatic tendons under a microscope, they rarely find inflammatory cells. Instead, they find something called tendinosis: disorganized collagen fibers, increased cell activity, new blood vessel growth into the tendon, and an overall picture that looks more like a stalled healing response than an active fire.³ True inflammatory tendinitis is extremely rare in chronic cases. The umbrella term “tendinopathy” is now preferred in clinical and research settings because it describes the pain and dysfunction without assuming an underlying cause that usually is not there.

This matters for treatment. If inflammation were the problem, anti-inflammatory drugs and rest would be the logical fix. Because the actual problem in most chronic cases is disorganized tissue that has failed to repair properly, treatments that stimulate controlled loading and collagen remodeling tend to work better than strategies aimed purely at suppressing inflammation. You might still hear doctors use “tendinitis” casually, and for a genuinely acute flare-up in the first few days, some inflammation may indeed be present. But if you have been dealing with Achilles pain for weeks or months, the biology underneath your skin has shifted to a different process.

Symptoms and How They Progress

Achilles tendinopathy typically starts with stiffness in the back of the heel or lower calf, most noticeable first thing in the morning or after sitting for a while. Early on, the tendon may loosen up once you get moving, which makes it easy to ignore. Over time, the pain tends to show up during and after activity rather than just at the start. You may notice swelling or a thickened feel to the tendon itself. In more advanced cases, the pain can become constant and interfere with walking, not just exercise. The condition can be stubborn: recovery can take up to a year, and recurrence is common, particularly when people return to sport too quickly.⁴

People with Achilles tendinopathy also report lower overall quality of life than the general population, even when the pain itself is moderate. Reduced ability to exercise, difficulty with daily tasks like climbing stairs, and the frustration of a slow recovery all take a psychological toll.⁵

Midportion Versus Insertional Tendinopathy

There are two main types, and they behave differently. Midportion tendinopathy affects the middle section of the tendon, typically two to six centimeters above the heel bone. This is the more common variety in runners and active adults. Insertional tendinopathy affects the point where the tendon attaches to the calcaneus (heel bone) and is more often associated with bony changes. On ultrasound, the insertional group shows significantly more calcification and bony deformity at the attachment site compared to the midportion group.⁶ Insertional pain tends to be provoked by shoe pressure against the back of the heel, and it can overlap with other conditions at the same site, including retrocalcaneal bursitis and bony prominences sometimes called Haglund’s deformity.⁷

These overlapping conditions at the heel can make diagnosis tricky. Retrocalcaneal bursitis, for example, is inflammation of a small fluid-filled sac tucked between the tendon and the heel bone. It can exist alongside insertional tendinopathy or on its own, and MRI can help sort out which structures are involved.⁸ If your pain is right where the tendon meets bone and you feel a bony bump, the picture may be more complex than straightforward tendinopathy alone.

Risk Factors

Overuse is the most commonly cited risk factor, but “overuse” is a vague term. What matters is the mismatch between how much load the tendon is used to handling and how much you are asking it to handle. Training load has inconsistent effects on tendon structure in research: in one study on athletes, higher loads appeared to slightly improve the structure of the non-dominant Achilles tendon but had a slightly negative effect on the dominant one.⁹ That suggests the tendon’s response to load is not a simple “more is worse” equation. Sudden spikes in training volume, rather than high volume per se, seem to be the more consistent culprit.

Biomechanics also play a role, though not always in the direction people expect. A review of running-related Achilles injury risk found that high braking forces during foot strike showed clear evidence for increasing injury risk, while high vertical forces and a high foot arch were actually protective.¹⁰

Beyond mechanics, certain medications carry a well-documented risk. Fluoroquinolone antibiotics, a class that includes ciprofloxacin and levofloxacin, roughly quadruple the odds of Achilles tendon disorders according to a meta-analysis pooling data from multiple studies.¹¹ The risk climbs steeply when fluoroquinolones are combined with oral corticosteroids. In one large population-based study, people taking both drugs simultaneously had roughly a 19-fold increase in the risk of Achilles tendon rupture compared to those on neither.¹² That same study found that higher body mass index and a history of prior tendon rupture also increased risk. If you are prescribed a fluoroquinolone antibiotic and you have any Achilles symptoms, it is worth bringing that up with your prescriber.

Diagnosis

Most Achilles tendinopathy is diagnosed through a physical exam. A clinician will feel the tendon for thickening, tenderness, and swelling, and will ask about the pattern of pain with activity. For suspected ruptures rather than tendinopathy, the “calf squeeze test” is a reliable bedside tool. A clinician squeezes your calf; if the foot does not move downward, the tendon is likely torn. This test has a sensitivity above 0.96 for detecting complete tears.¹³

Imaging becomes useful when the clinical picture is unclear or the condition is not responding to treatment. Both ultrasound and MRI can detect tendon thickening, structural disorganization, and new blood vessel growth. A prospective study comparing the two found they had similar overall diagnostic accuracy for both insertional and midportion Achilles tendinopathy, with no significant advantage of one over the other.¹⁴ Ultrasound is cheaper, quicker, and lets the clinician examine the tendon in real time during movement, which is a practical advantage. MRI grading, however, was better at predicting clinical outcomes at 12 months in one two-year study, meaning more severe-looking changes on MRI tended to correlate with slower recovery, while ultrasound findings did not predict outcomes as well.¹⁵

One important caveat with imaging: abnormal-looking tendons are not always painful, and painful tendons do not always look abnormal on a scan. That same study found ultrasound identified abnormal morphology in only about 65 percent of symptomatic tendons, while also flagging abnormalities in some tendons that had no symptoms at all. Imaging is a supplement to, not a replacement for, clinical assessment.

Treatment: Eccentric Exercise as the Foundation

The single best-supported treatment for Achilles tendinopathy is a structured eccentric exercise program, meaning exercises where the muscle lengthens under load. The classic version involves standing on the edge of a step, rising up on your toes, then slowly lowering your heel below the step level. This is done in high repetitions, typically twice a day, over 12 weeks. The protocol sounds simple, and it is, but the evidence behind it is strong. Eccentric training in people with chronic Achilles tendinopathy has been shown to increase collagen production specifically in the injured tendon, something that did not happen in healthy control tendons in the same study. Pain scores dropped significantly, and all subjects in that trial returned to playing soccer afterward.¹⁶ Longer-term follow-up has confirmed that the structural improvements on imaging persist, with a localized decrease in tendon thickness and more normalized tissue at roughly four years.¹⁷

What makes eccentric loading work where simple rest does not? The prevailing theory is that controlled, progressive loading stimulates the tendon’s repair machinery. Recall that the underlying problem in chronic cases is disorganized collagen that has failed to remodel into its normal parallel alignment. Eccentric exercise appears to restart that remodeling process, gradually replacing disordered tissue with properly aligned fibers. Rest, by contrast, does nothing to address the structural disarray and can even weaken the tendon further through disuse.

Shockwave Therapy and Injections

Extracorporeal shockwave therapy (ESWT) delivers acoustic energy pulses to the tendon through the skin. A systematic review concluded that ESWT is safe and effective for midportion Achilles tendinopathy, and that combining it with eccentric exercises and stretching may be more effective than shockwave alone.¹⁸ That said, the evidence is not unanimous. A separate meta-analysis found that ESWT’s advantage over eccentric exercise alone, in terms of pain and function, was small and inconclusive in the short term.¹⁹ The honest read of the literature is that ESWT is a reasonable add-on when eccentric exercise alone is not enough, but it is not a standalone replacement for loading programs.

As for injections, platelet-rich plasma (PRP) and high-volume saline injections have both been studied. A randomized trial comparing PRP, high-volume injection, and sham treatment in chronic midportion Achilles tendinopathy found that all three groups improved over time, but high-volume injection produced faster early gains. By 24 weeks, both high-volume and PRP groups had significantly better function and pain scores than the placebo group.²⁰ These results are encouraging but come from a relatively small number of trials, and injections are not considered first-line treatment. They are most often tried after several months of dedicated rehabilitation have fallen short.

When Surgery Becomes an Option

Surgery is reserved for cases that have not responded to at least six months (and often longer) of structured conservative treatment. The most common approach involves debriding, or cutting away, the damaged tendon tissue and then repairing what remains. In a series of 50 tendons with confirmed tendinosis, about half could be repaired with a simple side-to-side stitch, while the other half had such extensive damage that surgeons needed to reinforce the repair with a flap turned down from the healthy upper tendon. Outcomes were generally favorable in both groups: the reinforcement group actually had a higher rate of excellent results, suggesting that thorough removal of diseased tissue followed by a robust repair can yield good outcomes even in severe cases.²¹ Recovery from Achilles tendon surgery, however, is a long process, typically involving weeks in a walking boot followed by months of graduated rehabilitation before a full return to activity.

Return to Activity and Recovery Timelines

One of the most frustrating aspects of Achilles tendinopathy is how long it takes to resolve. Researchers who have developed return-to-sport frameworks emphasize that the extent of tendon damage, your age and sex, the severity of your symptoms, and the specific demands of your sport all influence the timeline.⁴ Returning too early is the single most common mistake. Tendons heal more slowly than muscles because of their poorer blood supply, and the structural remodeling triggered by eccentric exercise takes months to consolidate. A useful rule of thumb is that the pain-and-stiffness pattern should have resolved during normal daily activities before you start reintroducing sport-specific loading, and sport-specific loading should progress through stages rather than jumping straight back to full training.

People sometimes assume the tendon is “fixed” once the pain disappears. In reality, the tendon tissue may still be remodeling for months after symptoms settle. A premature return to high-impact activity during that window is the setup for recurrence.

Prevention and the Role of Heel Lifts

Gradual progression of training load is the most commonly cited preventive measure, and for good reason. Beyond training management, orthotic heel lifts have attracted research interest as a way to reduce tendon strain. The idea is simple: raising the heel slightly reduces how far the ankle needs to bend upward during movement, which lowers the stretch and force on the Achilles. A study on runners found that an 18-millimeter heel lift significantly reduced peak Achilles tendon force and strain during running, primarily by decreasing ankle dorsiflexion and increasing the tendon’s mechanical leverage.²² A 12-millimeter lift also reduced tendon strain during walking.²³

For people with flat feet, custom arch-support orthotics also significantly reduced Achilles tendon load during running, performing similarly to heel lifts in that regard.²⁴ Heel lifts and arch supports are not a cure on their own, but they can be a practical tool during rehabilitation or for people who are prone to recurrence and want to reduce tendon strain without stopping activity entirely.

Achilles Pain in Children and Adolescents

Heel pain in physically active kids is common, but it usually is not Achilles tendinopathy in the adult sense. The far more frequent diagnosis is Sever’s disease, or calcaneal apophysitis, which is irritation of the growth plate at the back of the heel bone rather than degeneration of the tendon itself. It typically shows up in children between ages 8 and 14 who play running or jumping sports. Symptoms overlap with Achilles tendinopathy — heel pain during and after activity, morning stiffness — but the underlying problem is different and the condition is self-limiting, resolving once the growth plate matures and fuses. Treatment focuses on activity modification, cushioned heel inserts, stretching, and time.²⁵ If a child or young teenager has heel pain, jumping to a diagnosis of tendinopathy without considering Sever’s disease is a common misstep.