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title: "How to Make Painful, Sensitive Knees Stronger"
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## Related Articles

- [What Is Load Tolerance? The Missing Link in Solving Knee Pain](/blog/load-tolerance-knee-pain)

I frequently receive questions like this one: 

I am a woman who wants to strengthen leg bones & muscles ... but how to do that with my painful, sensitive knee joints? 

I have improved my knees over the last 10 years by going very easy on them, but now have osteopenia & weak thigh muscles! I feel completely stuck — don't know how to regain leg strength without harming my knee joints.

## What does it mean to be “strong”?

We need to be strong to live long, enjoyable lives. 

If our bones are weak, we are more likely to break them. 

If our muscles are weak, we become frail.  

Without sufficient force on your body – such as being sedentary – you’ll get weaker .  

A sedentary lifestyle fails to deliver the necessary forces for healthy, strong knees. 

However, if your body gets too much force – during a single impact or with repetitive movements – you’ll get injured.   

This includes traumas, such as falls or car accidents.

And injury may also happen when resuming physical activities without adequate preparation and recovery. 

To maintain your strength, or to get stronge r, you need the right volume and amount of force.  

But how we become stronger starting in mid-life is different .

When you were in your 20s and 30s, you could play whatever sport your friends suggested.  

Or go to the gym and use whatever machines were available.  

If we use a kitchen analogy, this is like throwing whatever vegetables happen to be in your fridge into the skillet. Dinner typically turns out tasty.  

  

Strengthening can still happen later in life, but rather than being like a stir fry, it’s more like baking.  

Unless you’re an expert baker, you’ll likely need a recipe.

You’ll likely need to precisely measure the amount of forces from your exercises and activities to achieve an ideal outcome.

## How to Strengthen Muscles & Bones

The woman who submitted the above question stated that she has been “going very easy” on her knees during the past ten years.  

She also indicated that she developed osteopenia (weaker bones) and weak thigh muscles. 

To stay strong, muscles and bones require consistent levels of non-painful force applied to them.  

And in the case of muscles, these forces must be fatiguing. 

So if you treat your knees gently, you won’t be able to place enough force on your leg muscles and bones.

And they’ll eventually get weaker. This is an example of “use it or lose it.” ( [source](https://pubmed.ncbi.nlm.nih.gov/25199941/) )

If your knees are painful or easily become painful – the force required to strengthen your bones and muscles will likely cause more knee pain.  

And this often results in weaker thigh muscles , also known as arthrogenic muscle inhibition. ( [source](https://pubmed.ncbi.nlm.nih.gov/34883466/) )   

However, you can avoid this frustrating situation if you know how to strengthen the inside of your knees before you try to strengthen your muscles and bones.  

( This is Phase Two o f [Inside-Out Knee Health](https://youtu.be/Wcs2HwW9XLw) . )

## Why Your Knees are More Sensitive

Pain-free knees exist in equilibrium.  

In a healthy knee joint, there’s a balance between the strength outside the knee and the strength inside the knee.  

The inside of a strong, healthy knee is able to absorb outside forces.  

Here’s how it works: 

The muscles on the front of your thighs (your quadriceps) straighten your knees.  

Your quadriceps start from the front of your hip and the upper part of your thigh bone.

And they attach onto your shin bone (via the patellar tendon/ligament, pictured below).

The hamstring muscles, on the back of your thighs, bend your knees. 

Your hamstrings (highlighted in teal, below) start from the bones that you sit on (ischial tuberosities) and attach on the back of your shin bones.

When these leg muscles contract, they pull your shin and thigh bones together, and this squishes everything in between your bones .  

This includes both the cartilage on the ends of your bones (labelled below as “articular cartilage”) and the synovial fluid (pictured below in yellow).

When it’s strong, your cartilage is a firm substance.  

And when it’s healthy, your synovial fluid is thick (like egg whites).  

Strong, healthy knees – your cartilage and your synovial fluid – are able to withstand more force (more “squishing”) without knee pain.  

If your knees are not strong and healthy enough to withstand muscle strengthening exercises, your knees will become sore, achy, stiff, or swollen .   

Cartilage isn’t able to deliver these painful messages to your brain because it doesn’t have nerve supply.  

Instead, the lining inside your knee (the synovial membrane pictured above) gets irritated when the cartilage isn’t strong enough to withstand forces from your activities and exercises.

## Why “Being Gentle” Won’t Make Your Knees Stronger

“Being gentle” with your knees may make your knees feel better.

But it won’t make your knees stronger.  

Like I mentioned above, strengthening inside your knees requires precision – when you’re no longer in your 20s or 30s, and when you have painful knees.  

It’s not enough to just be active.

Or use whatever leg machines are available at your local gym.

## The Biology of Strengthening

To get stronger, you must apply the right amount of force with the right frequency to your body.  

And over time, the intensities of these forces need to increase. 

In medical and scientific communities, this application of forces is known as mechanotransduction . ([source](https://www.nature.com/subjects/mechanotransduction#:~:text=Mechanotransduction%20refers%20to%20the%20processes,that%20elicit%20specific%20cellular%20responses.))

Forces cause changes in your body.  

For example, if you get really tired by lifting a heavy weight several times, the result will be minor damage to your muscles.  

This minor muscle damage releases chemicals that likely make your muscles feel sore.  

The chemicals also stimulate your body to repair the damage.    

Blood flow increases and brings the ingredients necessary to begin this process of adaptation . ([source](https://pubmed.ncbi.nlm.nih.gov/2657962/)) 

Given you rest sufficiently – typically around 48 hours – your muscles will recover and become slightly stronger than they were prior to that weight lifting session. ([source](https://pubmed.ncbi.nlm.nih.gov/30036284/))

To continue getting stronger muscles, you’ll need to advance the amount of force during subsequent exercise sessions by increasing the number of times you lift the weight, or by using a heavier weight.

## How to Strengthen Inside Your Knees

Mechanotransduction affects anything that’s alive in your body – so that’s everything from muscles and bones, to tendons and even cartilage.  

Since cartilage has little to no blood supply, the forces that result in maintaining or improving cartilage strength must be lower in intensity, but higher in repetitions.

Here's a [guide](https://enjoystrongerknees.com/) to get started:

You can access it [here](https://enjoystrongerknees.com/) .

By applying the right amount of force , your cartilage not only absorbs the forces, but it also causes the cartilage to adapt , to become more firm and more capable of withstanding forces that would have previously caused injury. ( [source](https://pubmed.ncbi.nlm.nih.gov/34669175/) )

Softer cartilage is weaker. ([source](https://pubmed.ncbi.nlm.nih.gov/29083563/)) 

It can be more easily damaged.  

But after it becomes more firm, your cartilage is stronger because it can withstand greater amounts of force.  

In response to force, stronger cartilage will deform slightly and then return to its original shape without being harmed . ([source](https://www.mdpi.com/2075-1729/11/4/302)) 

To identify the correct forces for your knees, you first need to determine how strong your knees are.

## Determine the Strength of Your Knees

Muscle strength is frequently determined by assessing the most weight you can possibly move if you only have to do so one time (a one repetition maximum).  

An often safer way to determine muscle strength is identifying what weight allows you to complete a movement several times with good form, while achieving enough fatigue that you couldn’t complete the movement more than a few more times (a 10 repetition maximum). 

If you don’t have a sense of this, you may use a weight that is too heavy and potentially injure yourself.  

Or you may use a weight that is too light and your muscles won’t get stronger.  

The strength of the inside of your knees is different.  

Knee strength is the ability of the fluid and the cartilage to withstand force – without harming your knees, and without resulting in pain during or after a movement.  

Most medical and fitness professionals don’t measure knee strength.  

They try to measure muscle strength, but that measurement is invalid in the presence of pain or symptoms.  

And if you don’t measure it, it’s impossible to know what amount of force will improve your knees.  

You’re likely to use too much force (and get injured), or too little force (and your knees won’t get stronger).

If you're like most people, when your knees feel better, you'll try something like taking the stairs. 

And sometimes this results in your knee pain returning .

  

In this case, your muscles are certainly strong enough to take the stairs.

However, your knees are not.  

The surfaces (cartilage) and the fluid inside your knees are unable to withstand the force of taking the stairs without causing pain.

Knee strength, not muscle strength, is typically the limiting factor .

I measure knee strength by determining Load Tolerance. 

Load Tolerance is the amount of pain-free force you can produce or absorb for a specific movement , over a specified period of time, and still control the movement.

## One Type of Load Tolerance

You likely want your knees to be strong and healthy enough to sit down on a chair, toilet, couch, etc., without pain. 

And you probably want your knees to feel good when you get out of a car or rise from a seat on a plane.  

You may want your knees to feel good as you get up and down from the floor. 

Or when you hike unlevel trails or play sports. 

All of these activities have something in common: your knees are moving while your feet are on the ground.

Your knees are supporting your body weight as they’re bending and straightening. 

Let’s consider sitting down on a standard chair (without using your hands for support). 

Half of your body weight is supported through your left leg.

And the other half of your body weight is supported by your right leg. 

If you can sit down and stand up from a chair 5 times in a row – without using your hands and without any knee pain – both your right and left knees tolerate 50% of your body weight . 

And they may tolerate more than this.

But if you have knee pain – even a little bit – then your knee tolerates less than 50% of your body weight. 

But how much less?

## Accurately Measuring Your Knee Strength

If you’re baking, you’ll need tools like measuring cups and spoons.

Or possibly a small scale to weigh ingredients. 

Accurately measuring the correct force for your knees requires more than guesswork .  

I’ve found that the best tool to measure the strength of your knees is a [Variable Incline Plane](https://youtu.be/e3ejkSK-c4c) (VIP). 

This piece of equipment allows you to bend and straighten your knee using a fraction of your body weight.  

(By the way, I don’t have an affiliation with any of the companies that sell this type of equipment.)

One of the most common brands is Total Gym. 

When someone lies down on a six-level Total Gym machine that is set at level two, they are using 20% of their body weight.  

If they are bending and straightening both knees together, each leg is using force equal to 10% of their body weight.

Let’s say your left knee is strong and pain-free, but you’ve been having right knee pain. 

Here’s how I might guide you in measuring your right knee strength:   

- Lying down on your back on the Variable Incline Plane (VIP) at level 2 with your feet on the footplate, use both legs together to bend and straighten your knees 5 times. 
- If that feels good or neutral (to both knees, but in particular to your right knee), lift your right leg and bend and straighten your left leg 5 times. Notice how this feels.  
- Now, lift your left leg to bend and straighten your right knee 5 times. Does your right knee feel the same as your left knee did?

4. If your right knee feels good or neutral, increase the VIP level from level 2 to 3. 

     5. Repeat steps 1 through 3.

When you reach a level where your right knee is painful – even if the pain is minimal – you have exceeded the strength or the Load Tolerance of your knee.  

(Note: this amount of knee strength is often much less force than your muscle strength.)  

If for example, you have right knee pain at level 4 but not at level 3, your right knee strength is at level 3.

Level 3 on a six-level Total Gym machine is 28% of your body weight. 

If you weigh 150 pounds, this means your right knee is strong enough to withstand 42 pounds of force.  

This is your [Squat Load Tolerance .](https://youtu.be/ukhPCzFbLmk)

Knowing this measurement helps me recommend the best activities and exercises.

 

Then, once someone performs the recommended exercises for a few weeks, I remeasure their Squat Load Tolerance.  

This measurement may now be up to level 5 (43% body weight). 

So their knee strength has clearly improved. 

Their knee can withstand roughly 65 pounds compared to previously only being able to tolerate 42 pounds.  

This is a cause for both celebration and caution.

  

While their knee is probably feeling better, activities that require tolerating at least half their body weight will likely cause pain.  

Something as seemingly benign as frequently sitting down and standing up from a chair without using their hands. Or taking the stairs.

## Estimating Your Knee Strength

You only need access to a standard chair to estimate your Squat Load Tolerance.  

If you can sit down and stand up from a chair 5 times in a row – without using your hands and without any knee pain – both your right and left knees tolerate at least 50% of your body weight. 

If one knee is painful – even a mild amount of pain – then your Squat Load Tolerance for your painful knee is less than 50% of your body weight.  

And if both knees are painful, that your Squat Load Tolerance for both of your knees is less than 50% of your body weight.

This estimate provides some insights regarding why certain activities cause your knees to hurt.   

There’s also something else that I want you to keep in mind. 

If you estimate your knee strength again a few weeks later, you may get the same result.  

For example, your Squat Load Tolerance may still be less than 50% of your body weight. 

This may feel discouraging – unless you’re aware that it’s possible that your knees are still getting stronger.  

Your knees may have improved from 28% body weight to 43% body weight.  

In this case, your Squat Load Tolerance is still less than 50% of your body weight.

Your knees have improved, and you also need to continue getting stronger so that your knee pain won’t return during your preferred activities.

Here's a [guide](https://enjoystrongerknees.com/) to get started:

You can access it [here](https://enjoystrongerknees.com/) .

Key Takeaways:  

- Pain and sensitivity in the knees often stem from weakness in the internal knee structures (cartilage and fluid). 
- Load Tolerance is the best measure of knee strength.
- Applying the right amount of targeted, incremental force causes cartilage to become firmer and more resilient, and fluid to become thicker, more lubricating and a better shock absorber.  
- An inside out approach to knee health means improving the cartilage and fluid first to avoid re-injury and allow for safe muscle-building later.
- Knee strength gains may not always be obvious in daily tasks, so measurements clarify improvement is occurring.

Let's make knee pain history!

Laurie Kertz Kelly

When you’re ready to build  [Better Knees](https://betterknees.patientbase.io/services) –

with personal guidance :

Schedule a free 20-minute [Strategy](https://TheKelseyGroup.as.me/) [Session](https://TheKelseyGroup.as.me/) .   (Find your best time [here](https://TheKelseyGroup.as.me/) .)

[Learn more about Laurie Kertz Kelly](/about)

Disclaimer: The information in this blog post is for educational and informational purposes only and is not intended as medical advice. It should not be used to diagnose, treat, or prevent any health issue or disease without consulting with a qualified healthcare professional. The author of this blog and the website do not bear any responsibility for any actions taken based on the information provided in this blog.