I do stomach crunches, they're more effective for your abs than sit-ups and better for your lower back...working out alone likely won't aid completely with bloated belly though...you should start a food diary and find out what foods may be behind your belly bloating (common with having CD), but it's certainly a good idea to work out and using weights along with cardio is always best.
Yoga and pilates are also excellent to incorporate.
bee propolis caps 500mg one cap twice/day
omegas 369 caps one cap twice/day
probiotics 10 billion cfu once/day
vitamins C-calcium ascorbate (easy on the gut) and vitamin A each once/day
Prodiem fibre supplement one cap before bed
I've also altered my diet (no junky stuff at all, processed, fast-foods, refined sugars, ect) and exercise regularly.
I went from 30+ bloody BM's/day with lots of lower back pain to an average of 5/day no bleeding no back pain and completely formed stools, still have severe urgency issues.
~~~~~~~~My bum is broken....there's a big crack down the middle of it! LOL :)~~~~~~~~