Not so normal:
Cramping in your core muscles can make exercise uncomfortable, but it's usually just because your body is working so hard to keep up. The best thing to do is drink plenty of water and extend your cool-down to include plenty of full body stretches. In rare cases runners and weight lifters who train too hard can suffer from anaemia or bleeding of the colon. If pain in your stomach persists always visit a doctor.
SWISS BALL EXERCISES FOR A FULL BODY WORKOUT
THE 'FAST EXERCISE' 3 MINUTE WORKOUT IS INCREDIBLE
MORE GYM ADVICE