As far as I have been told in my previous 4 cycles, exercise is good. I contributed walking, swimming and running. I just held off completely during the TWW other than basic walking the dogs etc. I would check with your clinic though.
During stims, the risk is that if you do anything vigorous or involving twisting yourself about, you could end up suffering an ovarian torsion because your ovaries are so much bigger than usual. So, the above is generally to take it easy and avoid those types of activities.