Tendinitis: A Complete Guide — Causes, Types, and Prevention

Tendinitis

Tendinitis (or tendinopathy) is a generic term indicating a painful condition affecting a tendon — the fibrous structure that connects muscle to bone. It is one of the most common musculoskeletal pathologies, responsible for approximately 30% of all visits for musculoskeletal pain in sports and work settings.

The most frequent tendinitides include supraspinatus tendinitis (shoulder), lateral epicondylitis (jumper’s knee), and tennis elbow), Achilles tendinitis (Achilles tendon), patellar tendinitis (plantar fasciitis (plantar fascia of the foot).

In this complete guide, we will analyze what tendinopathies are, why they develop, how they are treated, and how they are prevented, with an approach based on the latest scientific evidence.

Tendinitis or Tendinopathy?

The Evolution of Understanding

The term “tendinitis” (with the suffix “-itis” indicating inflammation) has historically been the most used, but research over the last 20 years has shown that in most chronic tendinopathies, inflammation is minimal or absent. The predominant process is degeneration of the tendon tissue (tendinosis), not inflammation.

For this reason, the scientific community now prefers the term “tendinopathy”, which is neutral with respect to the pathological mechanism. In clinical practice, the two terms are still used interchangeably.

Tendinitis vs Tendinosis

Tendon Anatomy

The tendon is a fibrous structure composed mainly of Type I collagen (85-90%), organized into parallel bundles that provide tensile strength. The tendon:

• Transmits force from muscle to bone
• Has limited stretching capacity (4-8% of its length before rupture)
• Has poor vascularization (especially in “critical zones”) — which explains the slowness of healing
• Adapts to load: progressive loads strengthen it, excessive or insufficient loads weaken it

The “Critical Zones”

Each tendon has areas of low vascularization where tendinopathies are more frequent:

• Supraspinatus: critical zone 1 cm from insertion
• Achilles tendon: critical zone 2-6 cm above the calcaneus
• Patellar tendon: critical zone at the inferior insertion of the patella

Causes of Tendinopathies

The Continuum Model (Cook &038; Purdam)

Modern understanding of tendinopathies is based on the continuum model, which describes three stages:

• Reactive tendinopathy: response to acute overload. The tendon “swells” as an adaptive response. Reversible with load reduction.
• Tendon disrepair: if overload persists, the tendon enters a phase of “failed repair” with collagen disorganization. Partially reversible.
• Degenerative tendinopathy: degeneration is advanced, with areas of dead tissue and neo-vascularization. Difficult to reverse but manageable.

Extrinsic Factors (external)

• Overload: the most important factor — loading error (too much, too soon, too often) is at the root of most tendinopathies
• Repetitive movements: work or sports activities that stress the same tendon thousands of times
• Incorrect technique: in sports and at work
• Inadequate equipment: shoes, rackets, work tools
• Surface: hard ground, slopes

Intrinsic Factors (internal)

• Age: the tendon’s ability to adapt decreases after 35-40 years
• Sex: some tendinopathies are more frequent in women (calcific) or men (Achilles)
• Overweight: increases load on lower limb tendons and alters metabolic profile
• Diabetes: compromises collagen quality and healing
• High cholesterol: associated with tendinopathies (possible cholesterol deposition in tendons)
• Fluoroquinolones: antibiotics that weaken tendons
• Corticosteroids: local (injections) and systemic use weakens the tendon

Most Common Tendinopathies by Location

Shoulder

• Supraspinatus tendinitis: the most frequent, linked to impingement
• Calcific tendinitis: calcium deposit in the tendon
• Long head of biceps tendinitis: anterior shoulder pain

Elbow

• Lateral epicondylitis (tennis elbow): wrist extensors
• Medial epicondylitis (golfer’s elbow): wrist flexors

Wrist and Hand

• De Quervain’s tenosynovitis: thumb tendons
• Trigger finger: flexor tenosynovitis

Hip

• Trochanteric bursitis: gluteal tendons on the lateral aspect of the hip

Knee

• Patellar tendinitis (jumper’s knee): patellar tendon

Ankle and Foot

• Achilles tendinitis: Achilles tendon
• Posterior tibial tendinitis: arch of the foot
• Plantar fasciitis: plantar fascia (technically an enthesopathy)

General Symptoms of Tendinopathies

Pain

• Gradual onset: pain develops progressively, without a specific trauma
• Localized pain: at a precise point on the tendon, worsened by pressure
• Pain at the start of activity: which may improve with warm-up (warm-up phenomenon) and worsen afterwards
• Pain after activity: post-activity pain progressively increases as the tendinopathy worsens
• Morning stiffness: the tendon is stiffer and more painful upon waking

Typical Progression

• Pain only after intense sports activity
• Pain during and after activity, with improvement after warm-up
• Pain from the start of activity, which does not improve with warm-up
• Constant pain even in daily activities
• Pain at rest and at night

Evidence-Based Treatment

Eccentric Exercises: The Gold Standard Treatment

Eccentric exercises (muscle contraction during its lengthening) are the treatment with the best evidence for chronic tendinopathies. The mechanism:

• Stimulate remodeling of degenerated collagen
• Increase tendon resistance to load
• Reduce pathological neo-vascularization
• Have superior results to surgery in many studies

The Alfredson protocol (for the Achilles tendon) and derived protocols are the most studied: 3 sets x 15 repetitions, twice a day, for at least 12 weeks.

Load Management

The fundamental principle is load management, not absolute rest:

• Reduce the load that causes pain (do not eliminate it completely)
• Introduce strengthening load (progressive eccentric exercises)
• Avoid complete rest (the tendon weakens with inactivity)

Physiotherapy

• Progressive eccentric and isometric exercises: the core of the treatment
• Manual therapy: for associated dysfunctions (joint stiffness, trigger points)
• Shockwave therapy (ESWT): good evidence for chronic tendinopathies resistant to exercises
• Dry needling: can reduce pain and improve vascularization
• Taping: to reduce load on the tendon during activities

Medications and Injections

• NSAIDs: useful in the acute phase (reactive tendinitis), less effective in chronic (degenerative) tendinopathy
• Corticosteroid injections: effective in the short term (4-6 weeks) but with a risk of tendon weakening and recurrence. To be used with caution.
• PRP (platelet-rich plasma): promising but not yet definitive evidence
• Hyaluronic acid injections: some evidence for elbow tendinopathies

Surgery

Indicated only after the failure of at least 6-12 months of conservative treatment. Techniques include debridement (cleaning of degenerated tissue), tenotomy, and tendon repair.

General Exercises for Tendinopathies

For specific exercises for each tendon, consult the dedicated articles. Here are the general principles applicable to all tendinopathies.

Isometric Exercise (acute phase — reduces pain)

Isometric contraction

[IMAGE: Person sitting pressing their hand against a wall without moving their arm (isometric contraction of the supraspinatus). The elbow is flexed at 90 degrees, the arm is close to the body. The contraction is held for 30-45 seconds. Front view illustrating the principle of isometric contraction: the muscle contracts but there is no movement.]

Eccentric Exercise (chronic phase — remodels the tendon)

Calf eccentric on a step (example for Achilles tendon)

[IMAGE: Person standing on the edge of a step with the front of their feet on the step and heels in the air. The body starts in a high position (on toes) and slowly lowers below the level of the step (eccentric phase, 3-5 seconds). The upward phase is assisted by the healthy leg. Side view with the two positions (high and low) and an arrow indicating the direction of eccentric movement.]

Progressive Load Exercise (HSR — Heavy Slow Resistance)

Slow and controlled lifting with weight

[IMAGE: Person sitting performing a knee extension with an ankle weight (for the patellar tendon). The movement is very SLOW (3 seconds up, 3 seconds down). The weight is significant (not light). Side view with indication of the time for the concentric and eccentric phases.]

Prevention of Tendinopathies

• Gradual load progression: the 10% rule — do not increase volume or intensity by more than 10% per week
• Adequate warm-up: before any intense sports or work activity
• Regular eccentric strengthening: incorporate eccentric exercises into your training program as prevention
• Stretching: after activity, to maintain flexibility
• Variety: avoid monotony of movement (alternate activities)
• Adequate equipment: shoes, rackets, ergonomic workstation
• Weight control: overweight overloads tendons
• Avoid smoking and tendinopathy-inducing drugs: fluoroquinolones, corticosteroids

Frequently Asked Questions (FAQ)

Frequently Asked Questions

What is the distinction between tendinitis and tendinopathy?

Tendinitis traditionally referred to inflammation of the tendon. However, current understanding recognizes that chronic tendon pain often involves tissue degeneration and structural changes, leading to the broader term tendinopathy. This shift emphasizes a focus on tissue repair and remodeling rather than solely anti-inflammatory approaches.

Why is proper load management crucial for tendinopathy recovery?

Tendons respond to mechanical stress, and improper or excessive loading is a primary cause of tendinopathy. Effective load management involves carefully adjusting activity levels to stimulate tendon healing without overloading it, preventing further damage and promoting adaptation. This balance is essential for long-term recovery and preventing recurrence.

What is the primary role of a physical therapist in treating tendinopathies?

A physical therapist plays a vital role in assessing the specific tendinopathy, identifying contributing factors, and developing a tailored rehabilitation program. This often includes prescribing specific exercises, such as eccentric loading, guiding activity modification, and educating patients on proper movement patterns to facilitate tendon healing and restore function.

How do eccentric exercises contribute to tendon healing?

Eccentric exercises involve lengthening a muscle while it is contracting, placing specific tension on the tendon. This type of loading is highly effective in stimulating collagen production, improving tendon structure, and increasing its capacity to withstand stress. It helps remodel the degenerated tendon tissue and reduce pain over time.

Sources and Scientific References

1. Malliaras P (2022). Physiotherapy management of Achilles tendinopathy. J Physiother. 68:221-237. DOI | PubMed
2. Silbernagel KG et al. (2020). Current Clinical Concepts: Conservative Management of Achilles Tendinopathy. J Athl Train. 55:438-447. DOI | PubMed
3. Rudavsky A et al. (2014). Physiotherapy management of patellar tendinopathy (jumper’s knee). J Physiother. 60:122-9. DOI | PubMed
4. Muaidi QI (2020). Rehabilitation of patellar tendinopathy. J Musculoskelet Neuronal Interact. 20:535-540. PubMed
5. Charles R et al. (2023). The effectiveness of shockwave therapy on patellar tendinopathy, Achilles tendinopathy, and plantar fasciitis: a systematic review and meta-analysis. Front Immunol. 14:1193835. DOI | PubMed