Great Quads exercise, just make sure you have good single limb stance stability first.
Do you want a good quad burn? Try this exercise
This Quads exercise is a very good way to assess and also train frontal plane hip, knee, and ankle control. We at PhysioFitnessBC love to use it. As the moving leg goes in and out, the stationary leg has to stabilize you. The moving leg creates hip moments that the stationary hip has to match. At the ankle joint, the moving leg creates external pronation and supination moments which needs to be matched with equal internal moments in order to remain stable.
The goal is to try to your balance while moving the opposite leg. For better results try not to push off the moving leg.
We recommend sets of 20 to 30 seconds on each side. After that let us know how you will be walking the next day. Are you Quads sore? They should hehe