Based on my experience so far, running remains the best fat burner activity. I used to run every alternate days. Three to five kilometres around a running track at a go. I managed to maintain my weight, even loose some, during that time. Bear in mind though, I didn’t change my diet and was eating without reservations. But still, my weight remained in control. After the kids were born, I saw my weight steadily increasing. I barely had time to do house chores, nevermind running or tennis.