A Bad Date, and a Familiar Old Myth

A client of mine, I'll call him Carl, went on a date recently with a new physical therapist.

At some point his knee came up in conversation, and he mentioned the progress he'd been making.

"I'm rebuilding my cartilage," he told her.

"You can't do that," she said.

There was no second date.

Not because of the cartilage comment specifically, but the moment stuck with him enough to bring it up during his next coaching session, half as a joke, half as a genuine question.

If a physical therapist just a few months out of school still believes cartilage can’t be fixed once it's damaged, is it any wonder the rest of us do too?

It's a fair question.

And it's worth answering properly, because the belief that cartilage can't change is one of the most common things standing between people and a knee that actually improves.

The Mechanism: Why Cartilage Isn't as Fixed as You've Been Told

Cartilage has no nerve endings.

That single detail explains a lot about why this myth persists.

You can feel a muscle get sore after a hard workout.

You can't feel cartilage responding to load, so there's no internal signal confirming that anything is happening at all.

But cartilage is living, metabolically active tissue.

The cells inside it, chondrocytes, respond to mechanical signals like muscle and bone do, just on a slower timeline and without an immediate pain response to announce the process.

A 2023 systematic review and meta-analysis examined how joint loading activities like walking, cycling, and controlled weightbearing knee bends affect knee cartilage in adults, including those with or at risk of osteoarthritis (OA).

The review found that abnormal loading is considered a mechanical driver of osteoarthritis, yet moderate amounts of physical activity and rehabilitation exercise can have positive effects on articular cartilage.

That distinction matters.

It isn't load itself that's the problem.

It's a mismatched load, either too much or too little, relative to what someone’s cartilage can currently handle.

A separate review on cartilage mechanoadaptation describes cartilage as exquisitely sensitive to mechanical load, distinguishing between cartilage loss from disuse and cartilage loss from osteoarthritis itself.

These are two different processes that get lumped together in casual conversation, but behave very differently under a loading program.

And research on the biomechanics of knee osteoarthritis points to compensatory mechanisms within the joint.

Early on, compensatory mechanisms, such as increased synthesis of matrix molecules and proliferation of chondrocytes in the deeper layers of the cartilage, are able to maintain the integrity of the articular cartilage.

But those mechanisms may eventually get overwhelmed if the mismatch between load and capacity isn't corrected.

In plain terms: cartilage is always negotiating with the load you give it.

The goal isn't to avoid load.

It's to find the load your knee can currently handle, and build from there.

How the Inside Out Knee Health Framework Addresses This

This is exactly why Squat Load Tolerance sits at the center of the Inside Out Knee Health approach, instead of a generic list of strengthening exercises.

Phase 1 improves synovial fluid quality and reduces irritation, so the joint's internal environment is calm enough for real change to take hold.

Phase 2 uses the Variable Incline Plane (VIP) to directly measure Squat Load Tolerance, the percentage of bodyweight a person can squat without triggering pain.

This is the number that tells us whether the joint environment is actually improving, independent of how the knee happens to feel on a given day.

Phase 3 strengthens the external structures around the knee and rebuilds toward the loads that real, active life requires.

Common daily activities require more Squat Load Tolerance than most people realize.

Sitting on a couch, standing from a desk chair, and getting out of a car each require at least 50% Squat Load Tolerance just to complete without compensating.

When someone's tolerance sits below that threshold, ordinary days may feel like a series of small failures, even while the underlying tissue may already be adapting.

This is also why the VIP is a fundamentally different tool than a leg press.

A leg press machine tells you how much weight you can move.

It doesn't isolate or measure what a single knee joint can absorb or tolerate on its own, which is the actual number that matters for daily function.

What This Actually Looks Like (Not Generic Exercises)

Building cartilage strength isn't a list of exercises copied from a handout.

It's a progression built around a measured baseline.

This typically looks like:

  • Establishing a starting Squat Load Tolerance number, so progress has something concrete to be measured against.

  • Loading the joint just above its current tolerance in small, controlled increments, rather than jumping to a fixed program designed for a generic population.

  • Reassessing Squat Load Tolerance regularly, so the plan adjusts to what the joint is actually ready for, not what the calendar says should happen next.

  • Including muscular strengthening only after the joint itself demonstrates it can absorb more load, since Knee Joint Strength and muscle strength are not interchangeable.

This is also the reasoning behind describing the VIP as the best investment for knee pain.

It's not just a piece of equipment.

It's a direct measurement tool, which is what separates this approach from generic strengthening advice.

For Inside Out Knee Health,

here's a guide to get started:

You can access it here.

Mistakes People Make Around Cartilage and Knee Pain

Mistake 1: Treating a "Bad" X-ray or MRI as a Final Verdict

X-rays don't actually show cartilage well. They show the space between bones, and providers infer cartilage condition from that space. A grade 4, "bone on bone" reading doesn't mean your bones are literally touching. It means a physician is estimating based on an imperfect proxy, and plenty of people with that exact diagnosis still have meaningful cartilage remaining to work with.

Mistake 2: Confusing Muscle Strength With Joint Readiness

Someone can train consistently, build visibly strong quads, and still have a knee that can't tolerate the loads their life requires. Muscle strength and Knee Joint Strength are measured differently and improve on different timelines. Loading a joint before it's ready, even with strong muscles around it, can increase pain rather than resolve it.

Mistake 3: Expecting to Feel the Change in Real Time

Because cartilage has no nerve endings, structural improvement doesn't come with a sensation to confirm it's happening. People often quit a loading program right before it would have paid off, simply because nothing felt different yet. This is why tracking objective measurements matters more than relying on how the knee feels day to day.

The Reframing Insight

Here's the part that gets missed in almost every version of this conversation, including, apparently, on a first date.

Cartilage isn't something you fix once and then move on from.

It's something you're continuously negotiating with, the same way you negotiate with a muscle.

Use it appropriately, and it adapts.

Ignore it or overload it, and it doesn't.

The difference is that a muscle promptly tells you when it's unhappy.

Cartilage doesn't, which is exactly why guessing based on symptoms alone gets people stuck.

The "you can't do that" response isn't malicious.

It's what a lot of clinical training still emphasizes, sometimes even in newer physician and physical therapy graduates.

But it's an incomplete picture of what the tissue is actually capable of under the right conditions.

Frequently Asked Questions

Can cartilage actually get stronger, or is it fixed once it's damaged?

Cartilage responds to mechanical loading through cellular activity inside the tissue itself, not fixed once damaged. Research on cartilage mechanoadaptation describes articular cartilage as highly sensitive to load, capable of adapting in either direction depending on whether that load is appropriately dosed.

Why don't more medical professionals talk about this?

Much of clinical training has historically treated cartilage as tissue with little to no regenerative capacity, a framing rooted in older literature about cartilage's limited blood supply. Newer research on the biomechanics of osteoarthritis documents compensatory, adaptive responses within cartilage that complicate that older, simpler picture.

Does exercise help or hurt cartilage?

It depends entirely on the amount and type of load relative to the joint's current capacity. A 2023 systematic review and meta-analysis found that moderate joint loading activities can have positive effects on articular cartilage, while abnormal or excessive loading is associated with cartilage breakdown. This is why measuring Squat Load Tolerance, rather than assigning a generic exercise program, matters.

What is Squat Load Tolerance and how does it relate to cartilage?

Squat Load Tolerance is the percentage of bodyweight a person can squat without triggering knee pain. It functions as a direct, trackable proxy for how well the joint, including the cartilage inside it, is currently able to absorb and distribute force.

If my knee looks "bone on bone" on imaging, can cartilage still change?

Often, yes. X-rays infer cartilage loss from the space between bones rather than imaging cartilage directly, and a "bone on bone" reading doesn't necessarily mean no cartilage remains. Many people with a grade 4 diagnosis still have tissue to work with.

How long before I'd notice a difference?

Because cartilage has no nerve endings, structural change generally shows up in measurements, like Squat Load Tolerance on the VIP, well before it shows up as a felt sensation. This is consistent with how the body often adapts before symptoms catch up, which is why tracking objective numbers matters more than waiting to "feel" better.

Is this the same as what PRP or gel injections do?

No. Injections like PRP or viscosupplementation aim to improve the joint's chemical or inflammatory environment. Building Squat Load Tolerance through progressive, measured loading addresses the mechanical side of the equation, which is a different (and complementary) mechanism entirely.

Related Articles

Research References

For Inside Out Knee Health,

here's a guide to get started:

You can access it here.