Sit the floor with your leg straight and the other leg bend. Put the rolled towel under your knee if you are unable to get your knee straight. Your knee cap point to the ceiling.
Push down into the rolled towel and you can feel tighten the muscles on top of your thigh. Hold for 5 seconds. You can also lift your heel from the floor so that your quads engaged. You try to make sure your knee cap pulling up toward your body and see your muscle bulk of forming in your thigh you want to do it.
Common mistakes
Overactivation of the rectus femoris which is the biggest and longest muscles of quadriceps.
