Having a bag on your abdomen will not prevent you from doing the things that you used to do before surgery. The bag is pretty secure when snapped onto the wafer properly. Some individuals who are very active may use a strap or something of that nature to lightly press the bag against the skin to prevent it from moving about during strenuous activity.
As one patient just described, his wife sewed a pocket into his underwear to hold the bag so that it would not move around while he golfed and played tennis. You can even swim with the urostomy bag. The adhesive used to secure the wafer is quite strong.
With the stoma therapist, it is important that you identify the waistband of your sports clothing so that he or she can place the stoma in a location where both it and the bag will be covered.