The Tendon Pendulum: How Rehab Keeps Swinging Between Certainty and Confusion

From tendinitis and casting to PRP and progressive loading, the history of tendon rehabilitation is really the history of changing our minds.

There are few diagnoses in rehabilitation that have changed as dramatically as tendinopathy.

First it was inflammation.

Then we decided inflammation didn't exist.

Then everyone started talking about degeneration.

Then came eccentric exercise.

Then heavy slow resistance.

Then tendon neurobiology.

Now?

We're finally realizing the story was never that simple.

Unfortunately, plenty of clinicians are still practicing as though it's 1998.

Chapter 1: When Everything Was "Tendinitis"

For decades, every painful tendon became tendinitis.

Achilles tendonitis.

Patellar tendonitis.

Rotator cuff tendonitis.

Lateral epicondylitis.

If it hurt, it must be inflamed.

Treatment reflected that idea:

• Ice

• Ultrasound

• Anti-inflammatory medications

• Rest

• Cortisone injections

• Braces and splints

• Walking boots

• Casting

• Avoid painful movement

The assumption seemed logical.

Pain equals inflammation.

Except researchers kept examining chronic painful tendons and weren't finding the robust inflammatory infiltrates they expected (Khan et al., 2002).

Immobilize It and Wait

If inflammation was believed to be the problem, then the logical solution was simple:

Keep the tendon still.

For decades, painful tendons were commonly treated with braces, casts, walking boots, splints, and prolonged activity restriction. The thinking was straightforward: if movement irritated the tendon, removing movement would allow it to heal (Khan et al., 2002).

In some situations—such as an acute tendon rupture or immediately after surgical repair—temporary immobilization is absolutely necessary to protect healing tissue. But that approach gradually spilled over into the treatment of chronic tendon pain, where the evidence has proven far less supportive (Magnusson, Kjaer, & Langberg, 2010).

The problem is that tendons are living tissues that depend on mechanical loading to maintain their structure and function. Extended immobilization reduces collagen synthesis, decreases tendon stiffness and mechanical properties, and lowers the tissue's ability to tolerate future loading (Kjaer et al., 2009; Magnusson et al., 2010).

Patients often return from weeks in a brace or walking boot with less pain simply because they've stopped stressing the tendon—but they also return with a tendon that is less prepared for the demands of everyday life.

In hindsight, we weren't just treating inflammation.

We were often deconditioning the very tissue we were trying to heal.

That realization helped set the stage for one of the biggest shifts in modern rehabilitation: moving away from prolonged protection and toward progressive, well-managed loading (Cook & Purdam, 2009).

Chapter 2: The Pendulum Swings Too Far

In the late 1990s and early 2000s, work by Jill Cook, Craig Purdam, and others fundamentally changed how we viewed chronic tendon pain.

The word tendinosis became popular.

The tendon wasn't inflamed.

It was degenerating.

Collagen became disorganized.

Ground substance increased.

Cells looked abnormal.

Blood vessels grew into the tissue.

Suddenly clinicians proclaimed:

"There's no inflammation."

That statement became almost as inaccurate as the original one.

Chapter 3: We Accidentally Declared War on Inflammation

The phrase,

"Tendons aren't inflammatory,"

spread rapidly through courses, textbooks, and social media.

Reality?

Acute tendon injuries absolutely involve inflammatory processes.

Even chronic tendinopathy demonstrates immune cell activity and inflammatory signaling. It's simply not the overwhelming inflammatory response we originally imagined.

Modern tendon biology shows inflammation isn't binary.

It's regulated.

Localized.

Dynamic.

Changing throughout the healing process (Dean et al., 2016).

Chapter 4: Enter the Eccentric Revolution

Then Alfredson published his famous Achilles protocol.

Three sets.

Fifteen repetitions.

Twice daily.

Seven days per week.

Twelve weeks.

As a side note I don’t know any patient who actually completed this extensive and painful protocol, but I suppose if/when they didn’t we can blame the patient on “not doing their homework”.

Suddenly every tendon received eccentric exercises.

Some patients improved dramatically.

Many did well.

Some didn't.

Which raised an uncomfortable question:

Was eccentric loading uniquely beneficial?

Because as a non-contractile tissue, a tendon doesn’t know the difference between concentric, isometric, and eccentric loading.

Or was it simply one effective way to progressively load a tendon?

Chapter 5: Heavy Slow Resistance Changes the Conversation

Research comparing heavy slow resistance with eccentric programs found remarkably similar outcomes (Beyer et al., 2015).

It turns out tendons appear to care less/can’t tell the difference whether a contraction is eccentric or concentric...

...and far more about receiving an appropriate mechanical stimulus.

The conversation shifted from:

"Which exercise is best?"

to

"How much load can this tendon tolerate, and how should we progress it?"

Chapter 6: Pain Doesn't Equal Damage

One of the biggest lessons from tendon research is that pain and tendon structure often disagree.

Some terrible-looking tendons don't hurt.

Some painful tendons show relatively minor structural changes.

Ultrasound and MRI frequently reveal tendon abnormalities in completely asymptomatic athletes (Docking & Cook, 2019).

Sound familiar?

We've seen this same story with lumbar discs, menisci, labral tears, and rotator cuff pathology.

Imaging is one piece of the puzzle—not the entire diagnosis.

Chapter 7: Tendons Are Surprisingly Adaptable

Healthy tendons remodel.

They become stiffer.

Sometimes thicker.

They improve their ability to store and release energy.

Loading stimulates collagen turnover and improves mechanical properties, but adaptation occurs over months—not days (Kjaer et al., 2009).

This helps explain why patients often feel better long before imaging appears "normal."

Function usually returns before structure.

I think this actually strengthens the narrative because it shows that the field didn't just change its exercise philosophy—it also cycled through a series of increasingly sophisticated biological interventions. It fits well between the loading chapters and the modern rehabilitation section.

Chapter 8: The Injection Era — Looking for a Shortcut

If the "tendinitis" era was dominated by rest...

and the "tendinosis" era was dominated by loading...

the next chapter was dominated by injections.

The logic was always appealing.

If exercise wasn't enough, perhaps we could inject something that would accelerate healing.

For decades, corticosteroid injections were among the most common treatments for tendon pain. In the short term, they often worked remarkably well. Pain improved quickly, patients were happy, and everyone felt successful.

The problem?

The long-term results were much less impressive.

Systematic reviews consistently found that while corticosteroid injections often provide excellent short-term pain relief, they offer little long-term advantage over exercise and may even increase recurrence rates in some tendinopathies (Coombes et al., 2010).

As enthusiasm for corticosteroids faded, a new wave of biologic treatments emerged.

Platelet-rich plasma (PRP).

Prolotherapy.

Autologous blood injections.

Stem cells.

Tenocyte injections.

High-volume injections.

Each arrived with considerable excitement and the promise of stimulating tendon healing.

Some patients certainly improved.

But when higher-quality clinical trials accumulated, the results became far less convincing.

For most common tendinopathies, PRP has shown inconsistent or only modest benefits compared with structured exercise programs, and evidence for stem cell therapies remains preliminary (Fitzpatrick et al., 2017; Andriolo et al., 2019).

Shockwave therapy followed a similar trajectory.

Initially promoted as a way to "break up scar tissue" or stimulate healing, it has demonstrated benefits for some conditions—particularly calcific rotator cuff tendinopathy and selected cases of Achilles or plantar heel pain—but it is far from the universal solution it was once advertised to be.

The lesson isn't that injections or adjunctive therapies never work.

They probably do—for some patients, in some situations.

The lesson is that none of them consistently outperform a well-designed loading program.

Exercise keeps surviving every new treatment fad because tendons are mechanical tissues.

They adapt to mechanical stress.

No injection has figured out how to replace that.

Chapter 9: The Tendon Isn't Working Alone

One mistake rehabilitation still makes is treating the tendon like an isolated tissue.

An Achilles tendon doesn't function without:

• Calf strength

• Foot stiffness

• Hip strength

• Running mechanics

• Training load

• Sleep

• Recovery

• Overall metabolic health

Likewise, patellar tendon pain often reflects deficits well beyond the tendon itself.

The tissue matters.

The system matters more.

Chapter 10: Modern Tendon Rehabilitation

Today's evidence suggests tendon rehabilitation should be based on restoring function—not simply progressing through a list of exercises.

Phase 1: Calm the Tendon

Reduce irritability while maintaining as much capacity as possible.

• Relative load modification

• Education

• Isometrics (when appropriate)

• Maintain cardiovascular fitness

• Continue tolerable movement

Phase 2: Restore Movement

Normalize movement quality and reduce unnecessary compensations.

• Restore mobility where appropriate

• Improve strength of adjacent joints

• Address movement strategies

Phase 3: Build Capacity

Progressively increase the tendon's tolerance to force.

• Progressive isotonic loading

• Heavy slow resistance

• Unilateral strengthening

Phase 4: Build Rate of Force Development

Prepare the tendon for faster loading.

• Faster concentric movements

• Medicine ball drills

• Explosive strengthening

Phase 5: Restore Energy Storage

Reintroduce the spring-like function of tendon.

• Hopping

• Skipping

• Bounding

• Jump rope

• Running progressions

Phase 6: Return to Function

Gradually expose patients to the demands of work or sport.

• Cutting

• Sprinting

• Climbing

• Occupational tasks

• Sport-specific drills

Progress should be guided by tendon irritability—not simply by the calendar. Monitor pain during activity, symptoms afterward, and especially the tendon's response the following morning.

Remember that some tendons dislike compression as much as tensile loading. Insertional Achilles, gluteal, and proximal hamstring tendinopathies are common examples where compressive positions may need to be modified early before being progressively reintroduced.

Finally, don't just rehab the tendon.

Rehab the person.

Training errors, sleep, metabolic health, medications (such as fluoroquinolones or repeated corticosteroid exposure), recovery, fear of movement, and overall conditioning all influence tendon outcomes.

Clinical Reality

Every decade it seems, tendon rehab discovers a new miracle.

First it was rest.

Then ultrasound.

Then eccentric exercise.

Then heavy slow resistance.

Then PRP.

Then stem cells.

Then shockwave.

Through it all, one treatment has survived every fad:

Progressively loading the tendon.

That's not because exercise is trendy.

It's because tendons are living mechanical tissues. Whatever new treatment comes along, it still has to answer the same question:

Can this tendon tolerate a little more load than it could last week?

If the answer is yes, you're probably moving in the right direction. If the answer is no, the fanciest injection in the world isn't likely to save the rehabilitation.

-the Pissed-Off PT- like, subscribe, share-

References

• Alfredson H, Pietilä T, Jonsson P, Lorentzon R. Heavy-load eccentric calf muscle training for the treatment of chronic Achilles tendinosis. Am J Sports Med. 1998.

• Beyer R, Kongsgaard M, Hougs Kjær B, et al. Heavy slow resistance versus eccentric training as treatment for Achilles tendinopathy. Am J Sports Med. 2015.

• Cook JL, Purdam CR. Is tendon pathology a continuum? Br J Sports Med. 2009.

• Dean BJF, Dakin SG, Millar NL, Carr AJ. Review: Emerging concepts in the pathogenesis of tendinopathy. Surgeon. 2016.

• Docking SI, Cook JL. Pathological tendons maintain sufficient aligned fibrillar structure on ultrasound tissue characterization to explain why they can still load. Br J Sports Med. 2019.

• Khan KM, Cook JL, Kannus P, Maffulli N, Bonar SF. Time to abandon the "tendinitis" myth. BMJ. 2002.

• Kjaer M, Langberg H, Heinemeier K, et al. From mechanical loading to collagen synthesis, structural changes and function in human tendon. Scand J Med Sci Sports. 2009.

• Magnusson SP, Kjaer M, Langberg H. The impact of loading, unloading, ageing and injury on the human tendon. J Physiol. 2010.