What you must do: Sat on the glutei, the folded legs, the separated feet of the ground.
By contracting your abdominal muscles and by keeping the bust in the same position, unfold your knees by tightening the legs completely, then return to the starting position without putting back the feet on the ground.
Breathing: by carrying out this exercise expire (to empty the lungs) when you unfold your knees and inspire (to inflate the lungs) when evenez with the starting position.
