Exercise is important for everyone, but I personally feel it is essential to maintaining a good feeling for those with Colitis and Crohn's. I know it can be hard when a lot of the time you feel so tired and not really up for much, but keep it up, go for walks, get on your bike, do a routine and keep doing it.
At the moment, my morning's journey takes me about 30mins by bicycle, up a hill, the last stretch of which is quite steep, and it is about 20 mins to get back home in the afternoon. There are some mornings when I wake up and the thought of getting on my bike and making that journey seems far too difficult, but I do it, every day. I do it because I love my bike, and I refuse to let my Colitis be the boss of me and tell me I can't ride my bike. I won't let that happen. And it can be exhausting, and it can wear me out sometimes, but I feel so much better for it. I'm tired, but I feel energised at the same time, if that makes sense. And I know if I gave in and stopped cycling, and took the bus instead because it is easier, I would feel much worse and much more tired.
Now, 50 mins cycling a day could be too much for some people, I used to be a bicycle messenger, cycling the city for 7 to 8 hours a day, so I've known a high level of fitness in my time, so it is probably easier for me.
What I suggest for those who weren't at high levels of fitness to start with something easy, go for a walk, do a few sit ups, something, even when you are tired and don't want to get up, just do it, but of course take it easy.
Then push yourself a bit more, and a bit more, but only as far as you think you can go, and then go just that little bit more. And maintain it, do your choice of exercise every day or most days. It doesn't have to be a lot, as long as it is more than what you are doing now.
It works for me. Find what works for you. I hope it will help.