#8 – Bicycle Crunch
Deemed to be the single most effective exercise by researchers because it activated more ab muscle than any other exercise tested, this is an all-rounder that works the upper and lower ab regions as well as the obliques.
Lie flat on the floor with your lower back pressed to the ground and contract your core muscles. With your hands gently holding your head, lift your knees to about a 45-degree angle. Slowly, at first, go through a bicycle pedal motion, alternately touching your elbows to the opposite knees as you twist back and forth. Breath evenly throughout the exercise.