I always do quads, and they're not painful at all. You just have to be reasonably careful to get the right area of the quad, and not bang it in anywhere in the whole quad like I used to when I first started jabbing. You're better off looking up injection technique online to see exactly where it is, but if I had to explain the area I'd say it was about three inches square on the outside of the thigh, about five inches above the knee (but, obviously, not directly above the knee, because it's to the side of it). You won't have any problems there.