Does IBS affect how intensely I could exercise?

No. Your physical condition dictates how intensely you can exercise. People with IBS can be otherwise in great shape. You can, by the way, control symptoms of IBS with daily probiotics, fiber supplements, and peppermint oil capsules.
No. Exercise has no impact on ibs although it might improve constipation type ibs, remember to drink extra fluid at the rate of 20 ounces per 30 minutes of exercise.