Start standing in a wide stance position, with your knees slightly bent.
Transfer your weight over to your left leg, bending the knee so that your butt is slightly lowered into a squat.
Straighten your right leg out to the side, and lift both arms up above your head.
Tightening your core muscles, bring your right knee up to your chest as though you were kneeing an opponent. At the same time, bring your hands down to meet your knee.
Return your hands up above your head, and right foot back to the ground – don’t transfer weight into your right leg, instead repeat the knee-up motion at a rapid pace.