Air Bike Crunches
A great exercise for those days when you do not want to exercise but feel you have to and are not sure what you can do. Even if you do this for 30 seconds you gain in terms of benefits. The fact that you can do it fast or slow, in a piston-like movement (for efficiency) or an exaggerated circular, cycling fashion makes it as versatile an exercise as they come.
What's involved: Quads, front hip flexors, lower abs.
Powered by: Front hip flexors, primarily.
Tip: Raise your head to your chin and you also get to work out your upper abdominals and neck muscles at the same time.