stitches are caused by fluids/food in your digestive passage. THere are small ligaments holding your intestine in place. If you intestine is full of fluid/food, the ligament that supports that section will begin to hurt if you do any activity that shifts your weight up and down.
You should load up on fluids/food at least an hour before exercise - 1 1/2 hours is better though!
If you're still having problems, use a cv machine that doesn't involve moving your entire body up and down... the bike or rower for example
