Bicycle exercise for Flat stomach .. easy and free

The Bicycle exercise is the best move to target the rectus abdominis (i.e., the 'six pack') and the obliques (the waist),

according to a study done by the American Council on Exercise. To do this exercise correctly:

1. Lie face up on the floor and lace your fingers behind your head.
2. Bring the knees in towards the chest and lift the shoulder blades off the ground without pulling on the neck.
3. Straighten the left leg out while simultaneously turning the upper body to the right, bringing the left elbow

towards the right knee.
4. Switch sides, bringing the right elbow towards the left knee.
5. Continue alternating sides in a 'pedaling' motion for 12-16 reps.