Excercise also increases cervical mucus so a few light workouts around O time makes it easier for the swimmers to reach the egg. Since excercise raises body temprature which isn't good for sperms (especially if DH is wearing tight undies) make sure that DH doesn't workout to vigourously around O time and if he does its better to wait for a few hours afterwards so that he has time to produce some more sperms.