The mountain climber exercise is a great way to tone up those ab muscles, with a relatively short but intense burst. The starting position is similar to a straight arm press up with your arms locked and your body as straight as possible down to your feet. Pull your left knee up you towards your elbows, with your left foot touching the ground (as if you were in the blocks waiting to start a 100m race!), with your back right foot also on the floor but stretched out.
In a running motion, switch the legs so that the left leg bent up towards the elbows is straightened while at the same time moving the right knee up towards your elbows – and keep switching. Try to retain as stiff a position as possible with your back when switching legs from knees bent up to your elbows back to stretched out. Imagine that you are running as you switch the legs from bent knee to stretched out – do this for between 30 and 60 seconds with high intensity. Almost immediately you begin to feel the burn in your abs.