Achilles Tendinitis in Runners: Causes, Diagnosis, and Progressive Rehabilitation

Introduction

The Achilles tendon connects the calf muscle group (gastrocnemius and soleus) to the heel bone, and is the thickest tendon in the human body, bearing the highest stress. With every running footstrike, the Achilles tendon must withstand 6–8 times body weight. During a long-distance runner’s daily training, this tendon may repeatedly endure thousands of high-intensity tensile loads.

“Achilles tendinitis” is a catch-all term. Modern sports medicine more precisely classifies it as “Achilles tendinopathy,” emphasizing that this is a chronic degenerative condition rather than an acute inflammation, and the treatment approach is therefore fundamentally different.

Etiology Classification and Anatomical Location

Two Types of Achilles Tendinopathy

Paratendinitis is a separate condition, referring to inflammation of the sheath surrounding the tendon. Palpation reveals a “crepitus” sensation. It is an acute inflammation and requires controlling the inflammation first before proceeding with strengthening.

Major Risk Factors

• Training errors: Sudden increases in mileage, excessively high proportion of high-intensity interval runs, too much hill training
• Restricted ankle dorsiflexion: Insufficient ankle range of motion, forcing the Achilles tendon to compensate
• Insufficient calf strength: Especially eccentric control capacity during high-speed running
• Over-pronated foot (high arch): Increases torsional stress on the tendon
• Sudden shoe changes: Switching from high heel-to-toe drop shoes to zero-drop models without an adaptation period for the Achilles tendon

Diagnosis and Staging

Key clinical diagnostic points:

• Localized “fusiform swelling” in the mid-portion of the tendon, with marked tenderness on palpation
• Morning stiffness that eases with activity (but worsens after long runs)
• VISA-A score: A standardized tool for self-assessing functional status (out of 100; normal runners should score above 90)

Imaging: Ultrasound is the first choice, allowing assessment of tendon thickness, neovascularization, and the degree of structural damage. MRI is used when partial or complete tears are suspected.

Warning signs—suspected tendon rupture:

• A sudden “pop” sensation during running (as if kicked from behind)
• Positive Thompson Test: With the patient prone, squeezing the calf muscle produces no ankle plantarflexion
• This is a surgical emergency requiring immediate medical attention

Progressive Rehabilitation Program: The Alfredson Eccentric Training Protocol

The eccentric training protocol published by Swedish surgeon Håkan Alfredson in 1998 remains the gold standard for Achilles tendinopathy rehabilitation:

Training Exercises

Gastrocnemius eccentric strengthening (priority for mid-portion):

1. Stand on the edge of a step, bearing weight on the affected leg, with the heel hanging off
2. Use the healthy leg to rise up onto your toes to the top position
3. Shift all weight completely onto the affected leg
4. Slowly lower the heel of the affected leg below the step level, over 3 seconds
5. 3 sets × 15 repetitions, twice daily (morning and evening), for 12 consecutive weeks

Soleus eccentric strengthening (adding a knee-flexion variation):

• Same movement, but with the knee slightly bent (approximately 45°), which primarily targets the soleus muscle

Important principles:

• If pain-free, gradually add resistance (wearing a backpack, holding dumbbells)
• Mild to moderate pain (1–5 on a scale) is acceptable, but should not exceed 5, and pain should return to baseline within 24 hours after exercise
• Simultaneous fast concentric training (such as jumping rope) is not recommended

Modified Protocol for Insertional Type

The insertional type is not suitable for heel-drop exercises (which increase compression against the heel bone). Instead:

• Perform eccentric lowering on flat ground (heel not lowered below the horizontal plane)
• Add isometric training: holding an isometric ankle contraction in a wall-sit position, 45 seconds × 5 sets, which provides excellent immediate pain relief

Return-to-Running Staging

• Weeks 1–4: Complete cessation of running; perform eccentric training + maintain cardiovascular fitness (swimming, cycling)
• Weeks 5–6: If resting pain has significantly improved, begin brisk walking; try running 5–10 minutes and observe the response
• Weeks 7–10: Progressively increase running volume while maintaining daily eccentric training
• After week 12: Assess VISA-A score; if 80 or above, normal training can resume

Practical Advice

Shoe transition period: If currently using zero-drop running shoes, switch back to an 8–10 mm heel-to-toe drop model to decompress the tendon. After rehabilitation is complete, if you wish to switch back, reduce the drop by 2 mm every 2 weeks to give the tendon adequate adaptation time.

Massage and foam rolling: Foam rolling the calf muscle belly (avoid rolling directly on the tendon) helps improve tissue elasticity. Perform for 2–3 minutes after each training session.

If 12 weeks of conservative treatment fails: Consider ultrasound-guided PRP (platelet-rich plasma injection). This service is now widely available at major sports medicine centers in Taiwan, with partial coverage by the National Health Insurance.

Conclusion

Achilles tendinopathy is a marathon that requires patience. The effects of eccentric training are not immediate; it typically takes 6–8 weeks before noticeable improvement is felt. However, runners who persist with the program will, in the vast majority of cases, make a full recovery—and may even end up with stronger tendons than before the injury.

Related Reading

• Achilles Tendinitis: The Heel Problem Runners Fear Most
• Conservative Treatment of Achilles Tendinitis and Return-to-Training Criteria
• Achilles Tendinitis: A Complete Management Guide for Cyclists and Runners
• Calf and Ankle Strengthening for Runners: Preventing Achilles Tendon Problems