Your muscles grow in size according to your use of them, and they shrink down to where they need to be when your use decreases. My father was a MS patient, and was bed ridden. Because he could no longer walk, his muscles atrophied. They got NO USE AT ALL. His muscles then turned to fibrous tissue, and he then would never have been able to use them after they atrophied. But my father never got that well. I lost him in 1993.
Atrophy of the muscles in sick patients will draw their legs up to their chest and such, or sometimes behind them. I don't think you need to worry about that.

As long as you are walking/ and doing some form of exercise with your muscles/ you will be fine.