When (aged about 9 or 10, I think) I broke my collar bone, I was given some exercises to do by a physio. I was supposed to do them two or three times a day. But when I had the not-so-bright idea of doing a set while the rest of the class was doing PE, I got into real trouble with the PE mistress, who said if I was mended enough to be doing stretching exercises, I was mended enough to be doing gym.