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Bodybuilders refer to the vastus medialis, or VMO, as the teardrop muscle. That’s the shape that a well-developed lean, VMO muscle looks like. But you don’t have to be a bodybuilder to benefit from a VMO-centric workout. It just so happens that this muscle is the key to building strong knees.

How the VMO Strengthens the Knees

The VMO is one of the four muscles that make up your quadriceps. Of the four it is the one that most directly contributes to knee extension. Every time you take a step, stand up or kick a ball, your VMO muscle is doing the vast majority of the work.

The VMO is also a critical stabilizer of the knee. As such, it prevents the knees from caving in when you are carrying a load. This muscle attaches to your patellar (lower leg) bone as well as the femur (upper leg bone). It therefore serves to maintain the proper alignment between these two bones. This is especially important when you perform compound joint actions like squatting and dynamic multi-directional movements.

On the other hand, if you have weak VMO muscles, you may suffer from knee valgus, when the knees cave in toward each other when any sort of resistance is put upon the lower body.

Another problem that may arise in people with weak VMO muscles is known as patellofemoral pain syndrome. This condition comes about because the patellar becomes misaligned in relation to the knee joint and the femur. This causes knee pain every time you extend the joint. This is a common problem among young athletes who have not developed sufficient VMO strength to meet the demands of their athletic pursuits.

According to research that was published in Clinical Biomechanics, 75% of knee pain in adolescent girls is linked to patellofemoral syndrome.

You can check if your patellar is tracking properly with a simple test. Sit on a sofa with your legs extended out in front of you. Place a rolled-up towel under the knee of the leg that you suspect may be misaligned. Now put your fingers on the vastus medialis muscle as you contract it.

You should notice your knee pushing down into the towel and your foot should lift slightly off the sofa. You should also feel the VMO contracting under your fingers.

If the foot does not come off the sofa, it is a sign that you may be prone to patellofemoral syndrome. You would benefit from VMO strengthening exercises to overcome the problem before it worsens.

VMO Strengthening Exercises

There are a number of lower body exercises that directly strengthen the VMO muscle. The two best are the slant board Squat and the Leg Extension.

Slant Board Squat

When you perform the squat on a slant board you are put in a more biomechanically ideal position to activate the VMO muscles. That is because it is virtually impossible to round the back when squatting on the slant board. Back rounding overemphasizes the glutes, hamstrings, and erector spinae muscles while also allowing for knee tracking over the toes. This exaggerates VMO involvement in the exercise.

Here is how to do the slant board squat …

  1. Stand on the slant board with both feet completely on the board and relatively close together, your toes should be pointing forward. Clasp your hands together in front of your chest.
  2. Shift your entire body back as your pelvis tucks under the torso slightly.
  3. Maintaining this stacked position, with your rib cage over your hips, and inhaling. Then descend directly down to a bottom full squat position.
  4. Without a pause, exhale as you drive back to the top position.
  5. Keep your weight back through the heels as you perform a smooth, piston-like action to complete your rep count.

Leg Extension

The leg extension is performed on a leg extension machine. These are found in gyms but may also be part of a home multi-gym. You can also do the exercise on a chair with a resistance board attached to a secure upright.

Here is how to do the leg extension on a leg extension machine …

  1. Adjust the leg pad height and set the appropriate resistance.
  2. Sit on the machine with your ankles under the ankle pad.
  3. Grip the handles as you slowly extend your legs, stopping about 10 percent short of full extension.
  4. Lower under control until you are 10 percent short of the start position.
  5. Continue to perform your reps through this 80 percent range of motion.


The VMO muscle is the main muscle support for your knee joint. Keeping it strong will go a long way toward keeping your knees injury free. Perform 4-5 sets of the two exercises described above twice per week for best results.


Sheehan FT, Borotikar BS, Behnam AJ, Alter KE. Alterations in in vivo knee joint kinematics following a femoral nerve branch block of the vastus medialis: Implications for patellofemoral pain syndrome. Clin Biomech (Bristol, Avon). 2012 Jul;27(6):525-31. doi: 10.1016/j.clinbiomech.2011.12.012. Epub