I wanna tone up my arms a little more than they are right now, so what would be a good weight for me to use? My mom has always said if you use something to heavy it will break down your muscles. I use 5lb weights right now-I know that's not much but it keeps my arms it shape. I kinda thought about using something a big heavier to tone them up some though...cause I figure if I just keep using what I'm using now they'll always stay the same like they are right now. Would 8-10 lbs be ok?