Remission is the passive phase of the illness. There are no symptoms and you may be completely healthy for years. This is the time to build up your fitness level, so that you will be stronger if you get sick again.
When your illness is in remission, you can exercise without restrictions. Keep in mind, however, that even healthy and well-trained athletes may get uncomfortable gastrointestinal symptoms such as bleeding, nausea and pain when doing very strenuous exercise. Therefore, you should always listen to your own body and preferably consult your doctor before beginning a new physical activity.