While standing with a shoulder width stance, take a medicine ball and hold it at hip level. Do a front raise with the ball and rotate back and forth at the core. You should be moving at the hip and core and not at the shoulder. This exercise will torch your abdominals very quickly and will strengthen you abs very well.
Medicine Ball Standing Russian Twists - Start Position
Medicine Ball Standing Russian Twists - Finish Position
Medicine Ball Standing Russian Twists Exercise Video