This exercise is great if you do it correctly. It targets your obliques and is great for engaging the lower abs, which often get taken over by the upper abs. You'll need suspension straps of elastic cables. 

 

How to

Rest one leg while keeping the other straight. Your body weight should lean out of the anchor point. Stand holding a cable with one hand out in front of you at just under shoulder height. 

Keeping your arm fixed and straight and your abs engaged, rotate your upper body to the left, then back to centre.

Alternate sides for one set of 20 to 30 complete reps.

Photo credit: Keith Hamlyn

NEXT: Suspension training full body workout