I was doing sit-ups every morning before I played trumpet, and I did have some tenseness or "twitchiness" in the abdominal region, not really pain though. I found that after a while just playing trumpet was good enough to maintain my abs and develop six pack, so I switched to back extensions, to balance the work out, I think the sit-ups + trumpet playing were giving me back/neck pains and making me hunch over like Miles Davis. However, sit-ups helped for a while.