"Swimming
Quick results: Engages all major muscle groups, and is a strenuous workout for heart and lungs. Water supports body weight, so there's no stress on joints, and being about 14 times thicker than air, it offers ideal muscle-toning resistance.
Fighting flab: Prolonged exercise at lower intensity is better for fat-burning, which is why swimming is so effective - a man weighing around 70-80kg will burn about 750 calories an hour while swimming breaststroke at moderate intensity."