Achilles Tendonitis: Causes, Eccentric Loading &amp

What Is Achilles Tendonitis?

The Achilles tendon is the largest and strongest tendon in the body — the cable connecting the gastrocnemius and soleus calf muscles to the calcaneus (heel bone). It must absorb and transmit forces of up to 6–8 times body weight during running and jumping, making it vulnerable to the accumulation of microtrauma when loading exceeds the tendon's adaptive capacity. The resulting condition — Achilles tendonitis, more precisely termed Achilles tendinopathy — is characterized by pain, swelling, and progressive degeneration of the tendon matrix.

Achilles tendinopathy is one of the most common overuse injuries we treat at Balance Foot & Ankle, particularly in runners, court-sport athletes, and middle-aged recreational exercisers who have returned to activity after a period of reduced training. Unlike acute inflammation, which responds to rest and anti-inflammatories, Achilles tendinopathy is primarily a degenerative process (tendinosis) — the disorganized collagen response to repetitive microinjury. This distinction explains why rest alone rarely cures it and why the gold-standard treatment is controlled loading, not immobilization.

Insertional vs. Non-Insertional Achilles Tendinopathy

The location of the pathology determines both the clinical presentation and the treatment approach — these are functionally two distinct conditions:

Non-insertional Achilles tendinopathy affects the tendon mid-substance, typically 2–6 cm above the calcaneal insertion. This is the most common form (accounting for ~55% of cases) and the location where the Alfredson eccentric protocol works best. Patients describe a fusiform swelling and focal tenderness in this zone, pain that “warms up” with exercise, and stiffness after rest. The arc sign (the tender nodule moves with ankle range of motion) confirms the pathology is in the tendon itself rather than the retrocalcaneal bursa.

Insertional Achilles tendinopathy affects the tendon's attachment to the calcaneus. It is often associated with a Haglund's deformity (a prominent posterior-superior calcaneal bony prominence — “pump bump”) and retrocalcaneal bursitis. Insertional disease is more common in older athletes and is more resistant to eccentric loading (the Alfredson protocol actually worsens insertional tendinopathy because it increases insertional tensile load). Treatment for insertional disease requires modification of the standard eccentric protocol to avoid full plantarflexion, and heel lifts to reduce insertional tension.

Causes and Risk Factors

Achilles tendinopathy is a multifactorial overuse injury. The consistent risk factors we identify include: sudden increase in training volume or intensity (“too much, too fast”), inadequate recovery time between training sessions, running on cambered or hard surfaces, switching to minimalist footwear without adequate transition, tight gastrocnemius (which increases Achilles strain at any given ankle dorsiflexion), high BMI, male sex (men are affected 3:1 over women), fluoroquinolone antibiotic use (ciprofloxacin, levofloxacin — directly toxic to tendons and associated with spontaneous rupture), and systemic conditions including gout, rheumatoid arthritis, and hyperlipidemia.

The Alfredson Eccentric Protocol

The Alfredson eccentric heel-drop protocol is the most evidence-supported non-surgical treatment for non-insertional Achilles tendinopathy. Originally published by Håkan Alfredson in 1998 after he performed the protocol on his own Achilles (he reportedly could not get surgical clearance), it has since been validated in multiple randomized controlled trials with 60–90% good-to-excellent outcomes at 12 weeks.

The protocol: Stand on the edge of a step, affected foot only, heel hanging off. Use the unaffected leg to raise up on tiptoe. Lower slowly (3 seconds) on the affected leg only, allowing the heel to drop as far below the step as comfortable. This eccentric (lengthening) calf contraction applies load to the tendon as it elongates — the stimulus proven to drive collagen remodeling and matrix restoration. Perform 3 sets of 15 repetitions twice daily, 7 days a week. Progress resistance by adding a weighted backpack when the bodyweight protocol is pain-free. The protocol should be performed into mild-to-moderate pain — it is one of the few rehabilitation protocols where performing through pain is appropriate and predictive of good outcomes. Sharp, severe pain or acute post-exercise flares beyond 24 hours are signals to reduce load.

Important caveat: Do not use the standard Alfredson protocol for insertional tendinopathy. The deep plantarflexion at the end-range increases the posterior calcaneal lever arm against the insertion. A modified protocol performed on flat ground (no step) or with a heel raise avoids the problematic end-range loading for insertional cases.

Additional Treatment Options

Beyond eccentric loading, several adjuncts improve outcomes, particularly for cases not responding to the eccentric protocol alone:

• Heel lifts: A 10–12mm heel lift in both shoes reduces the maximum dorsiflexion angle during gait, decreasing tensile load on the Achilles. Simple, inexpensive, and immediately symptom-relieving — we recommend these as a first-line adjunct for all patients.
• Night splints: Maintaining 5–10° of dorsiflexion overnight prevents the calf and Achilles from shortening during sleep, reducing morning stiffness and improving the tendon's adaptation to the eccentric protocol.
• Extracorporeal shockwave therapy (EPAT): For chronic tendinopathy (symptoms >3 months) not responding to the eccentric protocol, EPAT applies high-energy acoustic pulses to stimulate neovascularization and collagen remodeling. Published meta-analyses show 60–70% success rates in appropriately selected patients. We perform EPAT in-office as a 3-session protocol.
• PRP injection: Ultrasound-guided platelet-rich plasma injection into the degenerative tendon core delivers growth factors that promote tendon matrix repair. Evidence quality is improving — several recent RCTs show PRP superior to saline placebo for chronic mid-substance tendinopathy. We use PRP for cases unresponsive to 12 weeks of eccentric loading and shockwave.
• Cortisone injection: NOT recommended for Achilles tendinopathy — multiple studies link peritendinous corticosteroid injections to increased Achilles rupture risk by further weakening already-degenerated tendon matrix. We do not inject cortisone into or adjacent to the Achilles tendon in any circumstance.

Surgery

Surgical intervention is reserved for cases that have genuinely failed 6 months of well-executed conservative care. For non-insertional tendinopathy: percutaneous longitudinal tenotomy (multiple small tendon incisions to stimulate a healing response) or open debridement of the degenerative tendon core with tubularization repair. For insertional tendinopathy with Haglund's deformity: endoscopic Haglundectomy (resection of the bony prominence) with or without Achilles tendon repair at the insertion. Recovery from Achilles surgery is prolonged — expect 4–6 months to full activity.

The Most Common Mistake We See

The most common mistake is using cortisone injections for Achilles tendinopathy. We frequently see patients referred after peritendinous cortisone injections from a primary care or urgent care provider. Cortisone does reduce pain temporarily, but it further weakens degenerative tendon matrix and significantly increases rupture risk. The correct treatment is controlled loading — the eccentric protocol — which is mechanically demanding to start but produces genuine tendon repair rather than masking pain while the tendon deteriorates.

Frequently Asked Questions

How long does Achilles tendonitis take to heal?
Non-insertional Achilles tendinopathy with consistent eccentric loading resolves in 60–90% of patients within 12 weeks. Chronic cases (symptoms >6 months) may require 6 months of combined eccentric loading, shockwave, and PRP before full resolution. Insertional tendinopathy is generally slower to respond — allow 16–24 weeks for complete symptom resolution.

Can I run with Achilles tendinopathy?
Continued running at reduced volume is generally preferable to complete rest — full rest leads to further tendon deconditioning and prolongs recovery. Reduce mileage by 50%, avoid speed work and hill running, and ensure the eccentric protocol is being performed daily.

The Bottom Line

Achilles tendinopathy responds best to controlled loading, not rest. The Alfredson eccentric heel-drop protocol — performed consistently twice daily for 12 weeks — produces 60–90% resolution rates for non-insertional disease. Heel lifts and night splints accelerate recovery. Shockwave and PRP are available for cases that do not respond to the eccentric protocol. Cortisone is contraindicated. If you have been told to rest and it hasn't worked, or if you have had multiple cortisone injections without lasting relief, come in for a proper evaluation — we will build you a loading program that actually repairs the tendon.

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Posterior tibial tendon issues often accompany Achilles tendinopathy — bracing can help both conditions. See our guide: Best Ankle Braces for Posterior Tibial Tendonitis.

Achilles tendinopathy and ruptures frequently require walking boot immobilization — following the right protocol improves outcomes. See our guide: Walking Boot Tips for Achilles Tendon Recovery.

For a complete clinical overview: Foot & Ankle Pain — Complete Guide — common causes, diagnosis, and podiatric treatment for all foot and ankle conditions

Complete Achilles Tendon Resource Library

Dr. Biernacki has written dedicated guides for every stage of Achilles tendon injury, recovery, and footwear:

• Rehabilitation: Achilles Tendon Eccentric Exercise Protocol — the Alfredson protocol and progressive loading program Dr. Biernacki prescribes for insertional and mid-substance tendinopathy.
• Surgery Recovery: Achilles Bone Spur Surgery & Recovery Time — timeline, success rates, and what to expect after retrocalcaneal exostosis removal.
• Anatomy & Diagnosis: Kager’s Triangle & Fat Pad — imaging findings and what they mean for Achilles pathology.
• Related Tendon Conditions: Peroneus Brevis Tendonitis · Peroneus Longus Tendonitis
• Best Footwear: Best Shoes for Achilles Pain · Best Shoes for Achilles Heel Pain · Shoes for Achilles Tendonitis · Best Shoes for Achilles Tendonitis · Best Sandals for Achilles Tendonitis