The best part of flutter kicks is you don't need any equipment to work all those muscles. All you have to do is lie on the floor, lift your legs to a forty-five-degree angle, and then "flutter" them ...

and how vigorously do you need to do it? We teamed up with Marie Murphy, Professor of Exercise and Health at Ulster University, to run an experiment. This concentrated on walking, the simplest ...

Sprint interval training refers to exercise routines where you run as hard ... These, too, were originally done on a bike, and you do the whole block once, not multiple times.