Sir,
I agree with most of what J.P.M. has said about fitness. But I think doing large numbers of sit ups are bad for the spine. Listen to what this guy says in this video. – Mr. Sport
JWR Replies: HJL and I agree that “crunches” rather than “sits ups” are the more appropriate exercise for most people of all ages. Not only are they inherently less damaging, but they also tend to be better for your back and can target the abdominal muscles more effectively. (That is, depending on how you position your hands and feet during crunches.)