What Is Achilles Tendinopathy?
Achilles tendinopathy is a painful and degenerative condition of the Achilles tendon — the largest and strongest tendon in the human body, which connects the gastrocnemius and soleus muscles to the calcaneus bone. The tendon supports forces of up to 12 times body weight during running.
The term "tendinopathy" replaced "tendinitis" in modern literature because histopathologic studies demonstrate that the chronic condition predominantly involves collagen degeneration (tendinosis) — with fibrillar disorganization, increased proteoglycans, and neovascularization — rather than active inflammation. True inflammation occurs only in the early and acute phases.
Two distinct clinical forms exist: mid-portion tendinopathy (2-6 cm above the insertion, more common in runners) and insertional tendinopathy (at the junction with the calcaneus, associated with Haglund deformity and retrocalcaneal bursitis).
Mid-Portion vs Insertional
The two forms differ in location, risk factors, and treatment response. Mid-portion tendinopathy responds better to eccentric exercise.
Continuum Model
Tendinopathy progresses through stages: reactive, disrepair (degeneration), and degenerative. Treatment changes by stage.
Overload Is the Key
The main cause is the imbalance between applied mechanical load and the tendon's adaptive capacity.
Epidemiology
Achilles tendinopathy is one of the most common injuries in runners and recreational athletes. Estimated incidence in runners is 7-9% per year, accounting for up to 11% of all running-related injuries. In the general sedentary population, prevalence increases with age, particularly after 40.
Risk factors include sudden increases in training volume or intensity, running on inclined terrain, footwear with excessive drop or worn-out shoes, limited ankle dorsiflexion, obesity, and use of fluoroquinolones (ciprofloxacin, levofloxacin). Diabetes mellitus and rheumatoid arthritis are risk factors for the insertional form.
Pathophysiology
The continuum model proposed by Cook and Purdam (2009) describes three stages of tendinopathy progression that guide treatment in a rational way. The stages are not necessarily linear — the tendon may oscillate between them depending on the load.
CONTINUUM MODEL OF TENDINOPATHY (COOK & PURDAM)
| STAGE | PATHOLOGY | CHARACTERISTICS | REVERSIBILITY |
|---|---|---|---|
| Reactive | Non-inflammatory proliferative response | Diffuse thickening, increased proteoglycans, no collagen disorganization | Fully reversible with load management |
| Disrepair (Degeneration) | Failed attempt at repair | Focal collagen disorganization, neovascularization, increased matrix | Partially reversible with treatment |
| Degenerative | Cell death and matrix loss | Acellular areas, disorganized collagen, extensive neovessels | Irreversible — focus on optimizing remaining tendon |
In the mid-portion, the zone of lower vascularization (2-6 cm proximal to the insertion) creates a "critical area" where regeneration is limited. In the insertional form, compressive stress between the tendon and calcaneus (especially in dorsiflexion) contributes to degeneration at the enthesis — for this reason, full-range eccentric exercises are contraindicated in this form.
The role of neovascularization is twofold: the neovessels are accompanied by nociceptive nerve fibers that contribute to pain, but they also represent a repair attempt. Treatments that destroy neovessels (sclerotherapy) relieve pain but do not necessarily improve tendon structure.
Symptoms
The clinical picture varies by location (mid-portion vs insertional) and tendinopathy stage. Pain is the main symptom, typically described as "morning stiffness" that improves with warming up.
Symptoms of Mid-Portion Tendinopathy
- 01
Localized pain 2-6 cm above the calcaneus
- 02
Morning stiffness in the tendon that improves after 10-15 minutes of walking
- 03
Palpable fusiform thickening in the tendon
- 04
Pain at the start of exercise that improves during and returns afterward
- 05
Palpable crepitus in the tendon during dorsiflexion/plantar flexion
- 06
Pain on climbing stairs or on inclines
Symptoms of Insertional Tendinopathy
- 01
Pain at the back of the heel, at the tendon insertion
- 02
Posterior bony prominence (Haglund)
- 03
Pain that worsens with closed shoes (pressure on the heel)
- 04
Pain that worsens with forced dorsiflexion
- 05
Swelling and redness in the posterior region of the heel
Diagnosis
Achilles tendinopathy diagnosis is essentially clinical, based on the history of load-related pain and physical examination. Imaging studies confirm suspicion and help differentiate mid-portion from insertional.
🏥Clinical Diagnostic Criteria
- 1.Activity-related Achilles tendon pain with morning stiffness
- 2.Palpable thickening and pain on palpation in the mid-portion (2-6 cm) or at the calcaneal insertion
- 3.Painful arc test (Royal London Hospital): pain that moves with the tendon during dorsiflexion
- 4.Pain on performing single-leg heel raise
- 5.Ultrasonography: tendon thickening (> 6 mm), focal hypoechogenicity, neovascularization on Doppler
Ultrasonography is the first-line examination: it demonstrates thickening (normal up to 5-6 mm), hypoechoic areas of degeneration, neovascularization on power Doppler and, in the insertional form, calcifications and enthesopathy. Magnetic resonance imaging is reserved for doubtful cases, suspicion of partial rupture, or surgical planning.
The most relevant functional test is the single-leg heel-raise count to fatigue. Fewer than 20 repetitions (or significant side-to-side asymmetry) indicates impaired tendon capacity and the need for progressive rehabilitation.
Differential Diagnosis
Pain at the back of the ankle and heel may have multiple origins. Differential diagnosis is essential to avoid ineffective treatments.
DIAGNÓSTICO DIFERENCIAL
Differential Diagnosis
Retrocalcaneal bursitis
Inflammation of the bursa between the Achilles tendon and the calcaneus. Deeper pain, on the front of the tendon.
Partial rupture of the Achilles tendon
Fiber rupture without complete loss of continuity. Acute pain with focal thickening.
Tarsal tunnel syndrome
Compression of the posterior tibial nerve. Pain and paresthesias on the medial ankle and sole of the foot.
Calcaneal stress fracture
Diffuse heel pain that worsens with weight-bearing. Common in runners and military personnel.
Soleus trigger points
Referred pain in the Achilles tendon and heel from soleus trigger points.
Treatments
Conservative treatment is the first line and resolves most cases in 3-6 months. Eccentric exercise (Alfredson protocol) is the cornerstone of treatment for the mid-portion, with level A evidence.
TREATMENT OPTIONS FOR ACHILLES TENDINOPATHY
| TREATMENT | MECHANISM | EVIDENCE | INDICATION |
|---|---|---|---|
| Eccentric exercise (Alfredson) | Collagen remodeling, fibrillar realignment | Strong (level A) | Mid-portion — first line |
| Heavy slow resistance exercise (HSR) | Similar to eccentric, better adherence | Strong (level A) | Alternative to eccentric |
| Load management (temporary reduction) | Allows recovery of the reactive tendon | Strong | Reactive phase — essential |
| Heel lift | Reduces tension on the tendon | Moderate | Insertional — reduces dorsiflexion |
| Extracorporeal shockwave therapy (ESWT) | Neovascularization, tissue regeneration | Moderate (level B) | Refractory cases > 3 months |
| Acupuncture / Electroacupuncture | Analgesia, local inflammatory modulation | Moderate | Adjuvant — pain control |
| High-volume injection (HVI) | Destroys neovessels and associated nerves | Emerging | Mid-portion with neovascularization |
Alfredson Protocol (Eccentric Exercise)
The protocol consists of slow heel drops on a step, with body weight on the affected leg. The eccentric phase (descent) is slow and controlled; the return to the initial position is performed with assistance from the contralateral leg. Perform 3 sets of 15 repetitions, twice a day (with the knee extended and with the knee slightly flexed), for a minimum of 12 weeks.
Mild pain during exercise (up to 5/10 on the visual analog scale) is acceptable and even expected. Load progression uses a weighted backpack once the exercise becomes painless.
Acupuncture as a Treatment
Acupuncture has been studied as an adjuvant treatment for Achilles tendinopathy. Some clinical trials suggest that acupuncture can deliver pain relief and functional improvement when combined with the eccentric exercise program, although the methodologic quality of available studies is heterogeneous.
The proposed mechanisms — based on experimental models and preclinical studies — include modulation of segmental nociceptive transmission, release of endogenous opioids, and possible effects on inflammatory mediators and local blood flow. These findings are predominantly mechanistic hypotheses and should not be taken as clinically confirmed effects in humans.
Electroacupuncture with alternating frequencies (2/100 Hz) is a modality frequently employed in clinical practice for chronic pain, based on preclinical studies that associate different frequencies with the activation of distinct endogenous analgesic systems. It can be useful when pain limits progression of the exercise program.
Laser Therapy (Photobiomodulation)
Laser therapy applied over the Achilles tendon has been used for analgesia and as a rehabilitation adjuvant. The proposed mechanisms involve the interaction of light with mitochondrial components of tenocytes, but the clinical translation of these findings is still under study.
Preclinical studies suggest that photobiomodulation may modulate matrix metalloproteinase activity (MMP-2, MMP-9) and influence tenocyte proliferation — findings that represent mechanistic hypotheses to be confirmed. In practice, combining acupuncture with laser therapy can be used as part of an adjuvant approach to the progressive loading program.
Prognosis
Mid-portion Achilles tendinopathy has a favorable prognosis with adequate conservative treatment. About 60-80% of patients achieve satisfactory results with the eccentric exercise protocol in 12 weeks. The insertional form tends to respond more slowly.
Recovery Timeline
Phase 1
0-2 weeksLoad Management
Temporarily reduce the provocative activity. Heel lift if insertional. Isometric exercises for analgesia (45 seconds, 5 repetitions).
Phase 2
2-12 weeksProgressive Eccentric Loading
Begin the Alfredson protocol (mid-portion) or floor-based eccentric exercises (insertional). 3x15 repetitions, twice a day.
Phase 3
3-6 monthsLoad Progression
Progressive load increase with a weighted backpack. Introduce kinetic-chain exercises — single-leg squat, step-up.
Phase 4
4-9 monthsReturn to Sport
Gradual return to running following 10% weekly progression. Capacity for 25+ single-leg heel raises without pain.
Myths and Facts
Myth vs. Fact
Achilles tendinopathy is an inflammation (tendinitis).
In the chronic phase, the predominant process is degenerative (tendinosis) — collagen disorganization and neovascularization, not active inflammation.
Complete rest is the best treatment for the tendon.
Prolonged rest weakens the tendon and reduces its load-bearing capacity. Progressive exercise (eccentric or HSR) is the treatment with the strongest evidence.
Anti-inflammatories cure tendinopathy.
NSAIDs may relieve pain temporarily, but they do not treat the underlying tendon degeneration. Preclinical studies raise the possibility of interference with collagen repair, a topic still under debate — medication use should be discussed with the physician.
If MRI shows degeneration, the tendon has no solution.
Tendon structure on MRI does not correlate directly with pain or function. Degenerated tendons can become asymptomatic and functional with adequate rehabilitation.
When to Seek Medical Help
Frequently Asked Questions about Achilles Tendinopathy
Achilles tendinopathy is a painful and degenerative condition of the Achilles tendon caused by repetitive overload. The term "tendinopathy" replaced "tendinitis" because the chronic phase involves collagen degeneration (tendinosis), not active inflammation. True inflammation occurs only in the first few days. Two forms exist: mid-portion (2-6 cm above the calcaneus, more common in runners) and insertional (at the junction with the calcaneus, associated with Haglund deformity). Treatment differs between the forms.
Eccentric exercise (Alfredson protocol) is the highest-evidence treatment for the mid-portion: slow heel drop on a step, 3 sets of 15 repetitions, twice a day, for 12 weeks. The Heavy Slow Resistance (HSR) protocol is an alternative with equivalent results. For the insertional form, exercises should be performed on the floor, without dorsiflexion beyond neutral. Combining with acupuncture facilitates load progression in the early phases.
It depends on severity. In the reactive stage (mild pain that disappears with warm-up), running can continue with a 30-50% volume reduction and avoidance of speed work and uphills. If pain persists during and after running, stop temporarily and substitute with non-impact activities (cycling, swimming). Return to running follows 10% weekly progression after achieving 25+ single-leg heel raises without pain.
Most patients with mid-portion tendinopathy show significant improvement in 12 weeks with consistent eccentric exercises, but full recovery may take 3-9 months. The insertional form tends to respond more slowly and may take 6-12 months. Factors that prolong recovery include: advanced degeneration, continued provocative activities during treatment, smoking, and diabetes.
Acupuncture probably acts through multiple mechanisms — based on preclinical and neurophysiologic studies — including modulation of local nociceptive transmission, release of endogenous opioids, and possible effects on inflammatory mediators and microcirculation. Electroacupuncture with alternating frequencies (2/100 Hz) is a modality used for chronic pain. Laser therapy, also as an adjuvant, has been linked in experimental models with effects on collagen and metalloproteinases. In practice, the most consistent benefit is facilitating progression of the eccentric exercise program.
Corticosteroid injection in or around the Achilles tendon is generally contraindicated because of the high risk of tendon rupture. Unlike other tendinopathies, the Achilles tendon has a lower capacity to tolerate the catabolic effects of corticosteroid. High-volume peritendinous injection with anesthetic and saline (High Volume Injection) is a safer alternative for tendinopathies with significant neovascularization.
Surgery is considered only after 6-12 months of adequate conservative treatment without satisfactory improvement, which occurs in 10-25% of cases. The options include open or arthroscopic debridement of the tendon, excision of insertional calcifications, and removal of the Haglund deformity. The rate of return to sport after surgery is 70-85%, but the postoperative rehabilitation period is 4-6 months.
Seek immediate medical evaluation if you feel sudden and intense pain in the calf with a sensation of being "struck" (possible Achilles tendon rupture), if you cannot stand on tiptoe or walk normally after an acute event, or if you notice a palpable depression along the trajectory of the tendon. Consult a specialist physician if pain persists for more than 2-3 weeks despite load reduction, if you are using fluoroquinolones and develop tendon pain, or if there is progressive thickening.
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