Why it made the list: This harder version of the Russian twist works the obliques while requiring the upper abs to contract isometrically. To recruit the obliques, you either need lateral flexion (bending to your side), trunk rotation (twisting), or sucking in your belly. Doing your twists works the trunk-rotation function of the muscle, so really focus on the contraction. Try to get a little crunch on either side after the rotation to up the ante.
If you're taking on healthy fitness and eating habits with the dream of achieving a six-pack, some real talk for you: "Very few people can achieve this look, regardless of what they do," says Stephen Ball, professor of nutrition and exercise physiology at the University of Missouri. "Most women who make this their goal will fail and ultimately give up on exercise all together." Way harsh, Tai.
Eat carbs. "There's this notion that carbs are bad and that you need crazy amounts of protein to be lean and fit," says Alcantara, who disagrees, and eats just as much carbs as protein, although the ideal ratio varies based on your goals. "Whatever you eat to get the results you want has to be sustainable, otherwise you're going to end up right back where you started with the same habits that got you there."