As with all things martial arts, fitness and exercise, the body parts that appear to be moving aren’t the part that are creating the physical action.
Your movement is always originating from your rooted foundation.
The leg that’s extended for a kick, isn’t doing the kicking, it is from the rooted that you energize from, you are actually spinning your energy against the floor to expanding internally, creating the shape of your kick.
In order to maintain your root and balance, do not straighten the leg you are standing on. The knee needs to stay soft in order to maintain the internal connection and body mechanics for your internal energy to flow, connecting with the feeling of the brain, executed from the dynamic of the mind.