I have health issues and fast to heal. Fasting is very hard (but beneficial) on my body so I do not exercise. I believe exercise is good for most people fasting but according to Dr Jason Fung author of the complete guide to fasting it should be moderate exercise. A long walk, weight lifting, swimming etc. I think HIIT would be too much. I would recommend listening to your body. Don’t push yourself when exercising. Fasting whether it’s for weight loss or repair is a time for healing.
I exercise during my fasts all the time usually I only do 3 day fasts I’m on a 5 day currently and did a hi intensity jump rope work out I usually have to work out upon waking up since I have high energy and I’m motivated at that point