Exercise of the Month - Peterson Knee Extension
17th November 2014
The Peterson Knee Extension
This is a great exercise for challenging the strength of Vastus Medialis. As a 'Closed Chain' exercise it challenges the tissue in a very functional way, and is one of the only exercises to strengthen VMO directly.
So why strengthen VMO functionally?
The usual root for developing strength in VMO is to perform seated knee extensions, which are great for isolating out the muscle but not so great for teaching the body how to integrate this strength. If your goal is improve patella tracking then a standard knee extension works well, but if your goal is to develop real world strength, where good overall tracking of the knee is required, then an open chain exercise doesn't cut the mustard.
The Peterson Knee Extension (Peterson Step-up) does a great job of training stability and alignment, as well as strength. You'll see in the video that the feet are placed in positions that are a little unstable. The top foot starts heel up and the lower leg balances on the heel, barely touching the floor. So the upper ankle develops stability as you improve your strength. To keep the knee tracking over the foot you'll need to find that place in your hip the keeps the femur neutral. This Gmax activation is an essential component of knee health, as well as ankle, hip, pelvis, lumbar, shoulder and neck health, so developing strength here is essential to far more than VMO alone.
The legs mostly experience the world in closed chain also. In the modern world open chain activities for the legs involve the swing phase of gait, which is unloaded, and a bunch of man made machinery like bikes (which don't activate VMO well if the saddle is too low), knee extension machines and leg presses in the gym. If you don't cycle or use the gym then I'd struggle to think of a loaded open chain movement that you might make, barring pulling a mud soaked, welly booted leg out of a puddle on occasion. Where as stance phase of gait, climbing stairs, squatting in and out of a chair, pushing you lawn mower etc require the legs to be loaded when in closed chain.
Now you can probably see from the positioning of the knee over the toes that this exercise would NOT be great for a client with acute cruciate ligament damage or other anterior knee pathologies like patellofemoral pain. There are a lot of loading forces due to the angles, so this is a late Stage 2 or Stage 3 exercise.
The major modification to this exericse for those struggling with it, is to to lower the step. Even a couple of inches of step is enough for some people in the beginning. I've had clients that get pain on knee extensions but have no pain on this exercise. Why? I believe it is in the direction of loading. A weighted knee extension causes the Tibia to experience torque between the heavy downward load distally and the strong upward pull proximally causing sheer in the joint. In the Peterson Knee Extension the degree of torque can be reduced by the height of the step. A low step, like a telephone directory (if such a thing exists anymore), reduces the distance the knee comes forward, so keeps the force directed through the tibia rather than across it, whilst a highter step subjects the knee to greater forces. Thereore, we can progress to greater degrees of stress at the knee by gradually raising the step.
Try the Peterson Knee Extension for yourself and see how much the whole leg gets worked. Once you feel confident that you can demonstrate this exercise with good technique, give it to your clients and see the improvements in knee health.
Watch the video above to see how ExerciseLab members allow their clients to learn this powerful exercise.