Strengthening the Quadriceps Muscles Does Not Reduce Knee Joint Force

This argument is in almost every article, book, protocol on how to overcome knee pain.

By strengthening your thigh muscles (quadriceps), you’ll reduce force on the joint and thereby reduce pain.

In fact, this idea was recently promoted in this article on using stair climbing for knee pain – as absurd as that might sound.

If you have knee pain, imagine climbing stairs to alleviate your pain and improve your function.

How exactly does that work?

In my experience, it doesn’t.

Let’s do some math though.

The force that goes through your knee when climbing stairs is at least 2-3 times your body weight.[source]

If you weigh, for example, 150 pounds, that force will be at least 300 pounds.

And if your knee hurts just walking around, it’s fair to assume that stair climbing will be well over what your knee can withstand.

Ok, fair enough. The basic assumption that climbing stairs with a painful knee will somehow make you better is, well, seriously flawed.

But one of the arguments for climbing stairs is that it will strengthen your knee muscles and that will then reduce the pressure or force going into your knee.

Unfortunately, that idea is also flawed.

First, it’s almost impossible to strengthen muscles in the presence of pain. The pain actually inhibits the muscle from contracting.[source] This happens not in the muscle itself but from your nervous system. It’s most likely a protective mechanism to keep you from creating more damage.

Second, muscle contractions increase joint loads and if you think about it for a minute, it makes sense.[source]

When the muscles contract, they pull on the bones compressing or squeezing the joint together which increases the joint force.

So, if strengthening your quadriceps increases joint loads, why does it seem to reduce knee pain in some people?

One, a main benefit of contracting your quadriceps muscle over and over is it increases the thickness, the viscosity, of the fluid in your knee called synovial fluid.[source] This fluid does a couple of things for your knee. It makes movement easier by reducing friction but it also acts as a kind of shock absorber.

Two, when you strengthen the muscles in your leg, you’re also changing the way your leg – hip, knee, and ankle joints- works. If you can strengthen the leg as a whole in a non-painful way, the joints tend to work together. Think of it as better cooperation so the force that must be managed is now not so much focused in your knee but also shared with the hip.[source]

Three, any time you actively pursue a solution and believe it will work, more often than not, you get better. Maybe not all better but usually some better.

Belief in what you’re doing is more powerful than the thing itself.

Four, you begin teaching your brain a new movement-pain relationship. As with any habit, when you move a certain way and hurt, your brain “wires” those things together. The more you do it, the firmer the connection becomes between the thing you’re doing and the pain experience.

This is one of the reasons we like a Variable Incline Plane. You can begin teaching your nervous system a movement pattern that doesn’t hurt in addition to doing some good things for your joints.

The idea that climbing stairs will improve your painful knee is flawed but strengthening your thigh muscles is a good thing to do. It improves the health of your joint which in turn will improve your ability to put weight on your leg.

Thanks for reading.

If you like this article, why not share it with a friend? If you’re interested in coaching services, please contact my colleague Laurie Kertz Kelly for a free, 20-minute Strategy Session by, clicking here. To get my Secret Weapon to fight knee, hip & back pain and stiffness, subscribe for free today.

Doug Kelsey has been a physical therapist and human movement expert since 1981. He is formerly Associate Professor and Assistant Dean for Clinical Affairs at the University of Oklahoma Health Sciences Center and the author of several books. He has conducted over 250 educational seminars for therapists, trainers, physicians, and the public and has presented lectures at national and international scientific and professional conferences. His professional CV is here.