This may not help but I can't tell when I'm weak until I try to do something. I have to test it out. I may stand up and be shocked at how strong my legs are, or at how weak they are...I can't feel it coming though. It could change also after a few steps, minutes, or a couple hours. I never know really what's coming. Until I actually go to use the muscles, though, I don't know how they are going to behave.