Tendinitis and Tendinopathy: The Most Common Overuse Injuries in Endurance Athletes

Rethinking “Tendinitis”

For a long time, tendon pain and injury were referred to as “tendinitis,” implying an inflammatory response. However, modern histological research has found that chronic tendon pain involves almost no inflammatory cells; instead, it is a degenerative condition—characterized by disorganized collagen fiber structure, neovascularization, and nerve ending proliferation.

Therefore, modern medicine increasingly favors the term “tendinopathy” to reflect its degenerative nature.

Physiological Characteristics of Tendons

• Main component: Type I collagen (approximately 85-90%)
• Blood supply: Very limited, hence slow repair rate
• Metabolic rate: Low; collagen half-life is about 2 years (skeletal muscle is only a few weeks)
• Function: Transmits muscle force to bone, and also serves as a “spring” that stores and releases energy

The low metabolic rate and limited blood supply of tendons explain why tendinopathy is so difficult to heal, sometimes requiring 6-12 months or more.

Common Tendinopathies in Endurance Athletes

1. Achilles Tendinopathy (Most Common)

Affected population: Runners (20-30% of running injuries), triathletes
Location: Main body of the Achilles tendon (2-7 cm from the heel) or the insertion point at the heel
Symptoms: Pain in the first few steps after waking in the morning, relief after activity, worsening after long runs

2. Patellar Tendinopathy (Jumper’s Knee)

Affected population: Runners, track cyclists (heavy gears)
Location: Inferior pole of the patella
Symptoms: Pain below the patella during downhill running or heavy-gear pedaling

3. Iliotibial Band-Related Tendon Issues

Affected population: Runners, cyclists
Location: Lateral knee or lateral hip (near the trochanteric bursa)

4. Pes Anserine Tendons (Medial Knee)

Affected population: Cyclists (those who ride with knees pinched inward)

5. Posterior Tibial Tendinopathy

Affected population: Runners (especially those with flat feet)
Location: Posterior to the medial malleolus

Stages of Tendinopathy Development

Jill Cook’s Continuum Model:

Stage	Characteristics	Reversibility	Management
Reactive tendinopathy	Reactive cell swelling after acute overload	Highly reversible	Load management, rest
Tendon dysrepair	Partial collagen disorganization	Reversible	Load management, eccentric training
Degenerative tendinopathy	Marked structural disorganization, areas of cell death	Partially irreversible	Load management, active intervention

Key principle: The earlier the intervention, the easier the full recovery.

Most Effective Treatment: Eccentric Training

Eccentric contraction is the contraction produced when a muscle is lengthened in the direction opposite to shortening. Research consistently shows that eccentric training is the most effective non-surgical treatment for tendinopathy.

Eccentric Heel Drops for the Achilles Tendon

The Alfredson Protocol (1998, still the gold standard):

1. Stand on the edge of a step with heels hanging off
2. Rise up on both feet (concentric), then lower slowly on the affected side only (3 seconds)
3. Repeat 3 sets × 15 reps with straight knee, and 3 sets × 15 reps with bent knee
4. Perform twice daily for 12 weeks

Important: Even if there is pain during training (but pain VAS ≤ 5/10), continue—this is a designed feature of the protocol.

Isometric Contraction Intervention for Patellar Tendon

Recent research shows that isometric training provides superior pain relief during the acute pain phase compared to eccentric training:

• Leg extension machine: 70% of maximal isometric strength, 5 sets × 45 seconds, 1-2 times daily
• Can be performed before and after training sessions to help reduce pain during that day’s workout

Load Management Principles

“Stopping training” is usually not the answer. Complete rest causes tendons to degenerate faster (because tendons need appropriate mechanical stimulation to maintain structure). The correct approach is load modification:

1. Acute phase (pain VAS > 5/10): Pause provocative activities; switch to low-load isometric training
2. Subacute phase: Introduce eccentric and isotonic training, gradually increasing load
3. Return-to-sport phase: Progressively resume running or cycling while maintaining strengthening work

The 24-hour pain rule: If pain 24 hours after training has not returned to pre-training levels, reduce intensity for the next session.

Adjunctive Treatment Options

Treatment	Scientific Support	Notes
Eccentric training	Strong	First-line treatment
Extracorporeal shock wave therapy (ESWT)	Strong	Option for those who fail conservative treatment
PRP injection	Moderate	Better long-term results than corticosteroids
Corticosteroid injection	Weak (short-term)	Short-term relief but potentially worse long-term outcomes
Ultrasound-guided hypertonic glucose injection	Moderate	Emerging treatment, increasingly adopted
Low-level laser therapy	Preliminary support	Adjunctive therapy

Preventing Tendinopathy

1. Progress training load gradually: Follow the 10% rule; avoid sudden spikes in volume
2. Maintain baseline strength: Sufficient lower-limb and core strength is the foundation of tendon protection
3. Allow adequate recovery time: Give tendons more than 48 hours to recover after high-intensity sessions
4. Heed early warning signs: Adjust immediately when localized tenderness appears; do not “push through”
5. Maintain training continuity: Returning to high intensity abruptly after a long break is a major trigger for tendinopathy

Conclusion

Tendinopathy is an injury that requires patience, but it is by no means incurable. By mastering the core principles of “load management + eccentric training,” most tendinopathies can fully recover. Most importantly: early intervention is more effective than watchful waiting—do not let an acute problem progress into chronic degeneration.

Related Reading

• Exercise Therapy for Tendinopathy: Achilles Tendon, Patellar Tendon, Rotator Cuff
• Achilles Tendinitis: The Heel Problem Runners Fear Most
• Achilles Tendinitis: A Complete Management Guide for Cyclists and Runners
• Conservative Treatment and Return-to-Training Criteria for Achilles Tendinitis