When people are informed that they will have to shift to an ostomy bag, there is understandably an upset reaction from them. They are dealing with something that will now be a part of their life and will impact the way they do things. New things have to be learned, and you have to figure out a new normal for yourself. There is understandably an adjustment period, but once that is over, a lot of people with colostomy bags end up living pretty normal lives and can do most things. Exercise with an ostomy bag is possible, so you can continue staying fit with a colostomy bag as well.
Of course, you cannot start exercising immediately because your body will need time to recover and get used to the new change. You can start off exercising with a physiotherapist present at first since it will introduce you to a range of exercises and make sure your form is correct.
Abdominal exercises can be a bit tricky since there is a risk of a hernia, but your doctor will correctly guide you here about how you can navigate this issue depending on your health condition. Another thing you do need to keep in mind is that ostomy bags tend to absorb more water, so you do run the risk of dehydrating yourself. This is why you will need to have water breaks throughout your workout.
You should also listen to your body because it will tell you when things are too much. If you are feeling tired, you do not have to push yourself. You can rest, and allow yourself to recuperate. The more you listen to your body, the better you will be able to move and figure out what works better for it as opposed to fighting it and potentially causing problems.