The level of activity during a fast would need to be judged on an individual basis and the reasons for fasting.
A faster who is emaciated, or anyone fasting for the recovery from serious disease, would not be ideal candidates as they need to preserve their energies and food reserves for the max' cleansing and healing to take place.
Activity also dissipates food reserves more rapidly and will shorten the length of a fast that may be needed in recovery.
However, anyone who fasts who is not fasting for any of the above, and especially those who desire to lose weight, then daily moderate activity/exercise would be recommended to those ends.