This is a bit silly.
I don't know about you but crouch walking is just as difficult as walking normally.
Go on, try it. Go and crouch around the house.
It's easy. Simple. Not hard. Especially not at the speeds used ingame.
If you want it to use stamina, make a sort of "crouch sprint" where you can go slightly faster while crouched and holding shift.
Otherwise, bollocks is crouching a "workout for your legs". It's just the same as standing up.