Arthritis (inflammation in joints) and arthralgia (joint pain) are the most frequent condition associated with IBD. The joints that are typically involved are the ankles, knees, hips, wrists and elbows.
In acute arthritis, it is important not to load the joints too much. It is, however, important to take care of the range of motion in the involved joints as well as to maintain muscle strength.
If walking is too painful for your joints, try biking or pool gymnastics. Exercising in water does not load your joints so much, but helps to maintain muscle strength and cardiorespiratory fitness.
For further reading:
Leirisalo-Repo, M., Hämäläinen, M. & Moilanen, E. (2002) Reumataudit. Rauma: Duodecim.