What Is Tendinitis? Symptoms, Causes, and Treatment

Tendinitis is inflammation or irritation of a tendon, the thick fibrous cord that attaches muscle to bone. It typically causes localized pain, tenderness, and stiffness near a joint, and it flares with movement or loading. The condition most often develops from repetitive motions or sudden increases in activity, though aging, metabolic conditions, and certain medications also raise the risk. What makes tendinitis tricky is that the word itself has become something of a catch-all: what people call “tendinitis” frequently turns out to be a different, longer-lasting process that does not respond to the same treatments.

Tendinitis Versus Tendinosis

The suffix “-itis” implies inflammation, and genuine tendinitis does involve an acute inflammatory response with immune cells flooding into the tissue. But research over the past two decades has shown that most chronic tendon problems involve degeneration of the collagen matrix rather than active inflammation. Histological studies of painful tendons overwhelmingly find disorganized collagen, increased blood vessel growth, and failed healing responses rather than the classic signs of inflammation. Newer techniques like immunohistochemistry have detected some inflammatory cells, muddying the picture somewhat, but the prevailing view is that chronic tendon pain is usually a degenerative condition called tendinosis rather than an inflammatory one.¹

Why does this matter to you? Because treatments aimed at reducing inflammation, like anti-inflammatory drugs and cortisone injections, may help an acutely inflamed tendon but do little for a tendon that has been quietly degenerating for months. The umbrella term “tendinopathy” covers both tendinitis and tendinosis and is what clinicians increasingly prefer, since it avoids implying a specific underlying process before one has been identified. Throughout this article, the word “tendinitis” appears where common usage dictates, but the evidence discussed applies broadly to tendinopathy.

What Tendinitis Feels Like

The hallmark symptom is pain at or near a joint that worsens when you use the affected limb. Tendinopathy commonly presents with localized tenderness, morning stiffness, and pain that spikes when you load the tendon, for example pushing off the ground with a sore Achilles or gripping a jar with a painful elbow.² Early on, you might notice pain only at the start of exercise that fades once the tissue warms up. As the condition progresses, pain can persist throughout activity and eventually show up during everyday tasks like climbing stairs or reaching overhead.

Swelling is sometimes visible, particularly along the Achilles tendon or the outside of the elbow. The area may feel warm to the touch in the acute phase. A gritty or crackling sensation when you move the tendon is another common sign, caused by roughening of the tendon sheath or the tendon surface itself. Reduced strength and range of motion often follow, partly because pain limits how much force you are willing to generate.

Where It Strikes Most Often

Tendinopathy tends to develop in tendons that cross major joints and endure high or repetitive forces. The most commonly affected sites include the rotator cuff tendons of the shoulder, the tendons around the elbow (both the outer side, known as “tennis elbow,” and the inner side, called “golfer’s elbow”), the patellar tendon below the kneecap, the hip abductor tendons on the outside of the hip, and the Achilles tendon at the back of the ankle.³ Wrist and thumb tendons are also frequent targets, especially in people who perform repetitive hand work. The common thread is that each of these tendons experiences high mechanical demand, and the tissue at the site of greatest stress or poorest blood supply tends to break down first.

How Tendons Get Damaged

Tendons are built to handle mechanical load, but they have limits. Under normal conditions, moderate and varied loading actually stimulates tendon cells to maintain and strengthen the collagen matrix. Problems arise when the loading is too much, too fast, or too repetitive, overwhelming the cells’ ability to repair microdamage before the next round of stress arrives.⁴

Animal studies have demonstrated this directly: tendons subjected to cyclical loading develop significantly more microtears than unloaded tendons, and the tears are larger, suggesting that repetitive stress kicks off a degenerative cascade.⁵ Interestingly, too little activity is also harmful. Chronic disuse leads to collagen disorganization and abnormal enzyme activity within the tendon, weakening it and predisposing it to injury when sudden demand finally comes.⁶ The practical takeaway is that tendon health depends on a middle zone of regular, progressive loading, not too much and not too little.

Risk Factors Beyond Overuse

Repetitive motion gets the most attention, but several other factors tilt the odds toward tendon trouble.

Metabolic conditions: Diabetes, abnormal cholesterol levels, and obesity each contribute to tendinopathy development. A systematic review and meta-analysis found that all three conditions raise the risk, with sex differences influencing which specific tendon is affected.⁷ In obesity, the mechanism appears to involve glycation of collagen, chronic low-grade inflammation, and oxidized lipids that impair tendon repair, although the exact causal chain is still being worked out.⁸
Age: Tendons lose water content, become stiffer, and repair more slowly as you get older. Blood supply to certain tendons diminishes with age, making them more vulnerable to degeneration and less capable of bouncing back from injury.
Certain medications: Fluoroquinolone antibiotics, a class that includes ciprofloxacin and levofloxacin, carry an established risk of tendon damage. A meta-analysis found that fluoroquinolone use roughly doubled to quadrupled the odds of Achilles tendon problems, and the risk climbed further in people over 60.⁹ The danger is sharply amplified when fluoroquinolones are taken alongside oral corticosteroids: one population-based study estimated the combined risk of Achilles tendon rupture rose roughly 19-fold in that scenario.¹⁰
Workplace ergonomics: Jobs that involve forceful gripping, sustained awkward postures, or highly repetitive hand and arm movements are linked to wrist and elbow tendon problems. Reducing the repetitiveness and forcefulness of work is a longstanding ergonomic recommendation, though it has been hard to prove in controlled trials.¹¹

Diagnosis

Most tendinopathy is diagnosed clinically. A physician palpates the tendon, tests your range of motion, and checks whether pain increases with specific resisted movements. If the picture is unclear, or if a partial tear or rupture needs to be ruled out, imaging comes next. Both ultrasound and MRI can reveal structural changes in tendons and have been validated against surgical and histological findings.¹² Ultrasound is often the first-line imaging choice because it is quick, inexpensive, and can be performed in the clinic during the same visit. MRI provides more detail and is better at assessing the surrounding soft tissue.

Researchers are also investigating blood-based biomarkers that could flag tendon degeneration before symptoms become severe. Elevated levels of certain signaling molecules, particularly VEGF (a growth factor linked to new blood vessel formation), have been found at significantly higher concentrations in the blood of patients with rotator cuff disease, and those levels correlated with disease severity.¹³ Multi-omics research has identified recurring candidate biomarkers, especially those involved in collagen breakdown and immune regulation, though none have reached routine clinical use yet.¹⁴ A reliable blood test for early tendon degeneration would be a game-changer for athletes and workers at high risk, but for now it remains a research goal.

Treatment That Works and Treatment That Doesn’t

The evidence on tendinopathy treatment defies some deeply held assumptions. The two pillars of early self-care, rest and anti-inflammatories, turn out to be more nuanced than most people expect.

Anti-Inflammatory Medications

NSAIDs like ibuprofen are the first thing many people reach for, and they can take the edge off acute pain. But in chronic tendinopathy, the evidence is surprisingly thin. A controlled trial in which patients with Achilles tendinopathy took ibuprofen for several weeks found no meaningful changes in tendon thickness, pain scores, or the expression of collagen-related genes compared with placebo.¹⁵ This makes sense in light of the tendinitis-versus-tendinosis distinction: if the primary problem is collagen degeneration rather than inflammation, suppressing inflammation is targeting the wrong process. Short-term NSAID use for acute flares is reasonable, but relying on it as a long-term strategy for chronic tendon pain is unlikely to fix the underlying issue.

Loading-Based Exercise

Progressive loading, meaning gradually increasing the demand on the tendon through structured resistance exercise, has become the cornerstone of tendinopathy rehabilitation. Two well-studied approaches are eccentric training (slowly lowering a weight so the muscle lengthens under tension) and heavy slow resistance training (lifting moderate-to-heavy loads at a controlled pace). A randomized trial comparing both methods in Achilles tendinopathy found that each produced lasting clinical improvement at one year, with heavy slow resistance tending to generate higher patient satisfaction at 12 weeks.¹⁶

Similar results have been seen in patellar tendinopathy. A trial comparing heavy slow resistance training, eccentric decline squats, and corticosteroid injections found that both exercise groups maintained their improvements at the six-month follow-up, while the injection group’s gains faded. Treatment satisfaction was highest in the heavy slow resistance group.¹⁷ The overarching message is that tendons need gradual, controlled stress to heal, not prolonged rest. Complete immobilization may actually delay recovery by depriving the tissue of the mechanical signals it needs to remodel.

Injections

Corticosteroid injections remain popular for quick relief, and they do reduce pain rapidly. But the same patellar tendinopathy trial described above found that benefits faded within months, and repeated or intratendinous corticosteroid exposure may impair collagen production and tendon-cell health, potentially weakening the tissue over time.¹⁸ Platelet-rich plasma (PRP) injections are an alternative that has generated interest. PRP delivers concentrated growth factors that can stimulate tendon-cell activity and support collagen remodeling. Several trials and reviews report more durable improvements with PRP than with corticosteroids, but the evidence is still evolving and PRP formulations vary widely between clinics.

Shockwave Therapy

Extracorporeal shockwave therapy (ESWT) delivers acoustic pulses to the affected tendon and has shown promise in several tendon conditions. A study covering elbow tendinopathy, Achilles tendinopathy, plantar fasciitis, and rotator cuff tendinopathy found significant reductions in pain and improvements in function and quality of life both immediately after treatment and at four-week follow-up.¹⁹ The evidence is strongest for calcific shoulder tendinopathy and plantar fasciitis. For Achilles tendinopathy specifically, recent data support its use, but conclusive recommendations are still lacking.²⁰ Shockwave is generally considered when exercise-based therapy alone has not produced enough improvement after several months.

When Surgery Becomes an Option

Surgery is reserved for cases that fail to improve with at least three to six months of structured conservative treatment. The most common procedures involve debriding (cleaning out) the damaged portion of the tendon, sometimes removing calcified deposits or bony spurs at the attachment point. A systematic review of surgical treatment for Achilles tendinopathy found an average success rate of roughly 83%, with a complication rate of about 6%. Minimally invasive techniques and open procedures had similar success and satisfaction rates, though complications tended to be somewhat lower with minimally invasive approaches.²¹

At the Achilles insertion specifically, surgical debridement using a transverse incision produced significant improvements in pain and function at a minimum of three years’ follow-up, with the vast majority of patients returning to their pre-injury activity level.²² For biceps tendinopathy at the shoulder, arthroscopic options include tenodesis (reattaching the tendon to a new point on the bone) and tenotomy (simply cutting the tendon free). Both produce satisfactory results, but tenotomy carries a higher rate of a cosmetic bulge in the upper arm, sometimes called a “Popeye deformity.”²³

What Happens If You Ignore It

Tendinopathy that goes untreated does not always progress, but it can. The most serious complication is tendon rupture. A healthcare database analysis found that about 4% of patients diagnosed with Achilles tendinopathy went on to sustain a rupture, with the highest rate (about 4.3%) in people aged 50 to 59.²⁴ A smaller clinical study using ultrasound to track patients with chronically thickened, painful Achilles tendons found that about 28% of those with significant structural changes eventually ruptured spontaneously. Crucially, no ruptures occurred in tendons that had been classified as structurally normal on ultrasound.²⁵ The implication is that ongoing structural deterioration, not just pain, is the real warning sign, and imaging can help identify people who need closer monitoring.

Beyond rupture, chronic tendon pain can gradually shrink your activity level. People give up sports, modify their exercise routines, or start compensating with other body parts, which can set off a chain of secondary problems in the knee, hip, or back.

The Psychology of Tendon Pain

One of the most underappreciated aspects of tendinopathy is how powerfully psychology influences outcomes. Kinesiophobia, the fear of movement or re-injury, is common in people with persistent tendon pain. A systematic review found that elevated kinesiophobia scores in Achilles tendinopathy were strongly linked to higher pain, lower quality of life, greater self-reported severity, and poorer performance on physical tests like heel raises.²⁶

A cross-sectional study of patients with Achilles or patellar tendinopathy found that psychological readiness to return to sport, pain catastrophizing, and kinesiophobia were all significantly associated with how well patients functioned, how much sport they participated in, and how satisfied they were with their recovery.²⁷ This creates a vicious loop: the tendon hurts, you move less, the tendon weakens from inactivity, and when you do try to move, the pain feeds the fear cycle. Progressive loading programs address this directly by reintroducing controlled stress in a graded way, building both tissue tolerance and confidence. But in patients with high fear-avoidance beliefs, explicit psychological support or education about pain science may be just as important as the physical prescription.

Prevention in Practice

Preventing tendinopathy comes down to managing the variables you can control. Gradual increases in training volume and intensity give tendons time to adapt. The commonly cited “10% rule,” increasing weekly training load by no more than 10%, is a rough starting point, though individual tolerance varies. Cross-training, alternating between activities that stress different tendons, spreads the cumulative load and reduces the chance of hammering one structure day after day.

For workers in manual occupations, ergonomic adjustments like tool redesign, task rotation, and reducing sustained force or awkward postures remain the primary preventive strategy. Footwear choices matter for lower-limb tendons: worn-out shoes with poor cushioning increase the mechanical demands on the Achilles and patellar tendons. Maintaining a healthy body weight and managing conditions like diabetes and high cholesterol address the metabolic side of risk. And if you are prescribed a fluoroquinolone antibiotic, especially if you are also taking a corticosteroid, it is worth asking your doctor whether an alternative antibiotic is available, particularly if you have a history of tendon problems.