You don't need muscles and legs to lucid dream. It's not a great exemple.The muscles for lucid dreaming is believing that you can.
That's why affirmations or autosuggestion is for... You program your mind for lucid dreams and that's all. Of course it may take some days.
But everything you need is a conviction that you can. Often when you do this you get vibrations every morning and you enter the LD.
It takes no other effort.