Abs are mostly made in the kitchen,but you can encourage speed the process along by doing high-intensity workouts that burn calories and build muscle. This is one aspect of every CrossFit workout, which is why even though CrossFitters rarely spend time solely working their abs, or they have amazingly strong,toned core muscles. You don't have to belong to a box (CrossFit gym) to accumulate six-pack abs. Here's a CrossFit workout designed by Jade Jenny, CrossFit coach and owner of Champlain Valley CrossFit, and that you can accomplish on your own. All you'll need is a jump rope and a sturdy bench or box.
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This CrossFit Exercise Is One of the Most Effective Ways to Tone Your AbsThe Workout: complete as many rounds as possible (AMRAP) in 10 minutes30 single unders (jumping rope)
20 AbMat sit-ups (diamond sit-ups)
10 burpees
5 box jumps (accomplish step-ups whether this is too difficult)
Source: popsugar.com