Lie on your back with knees bent to 90-degree angles. Straighten your arms by your sides, and lengthen your fingertips. Press the backs of your shoulders against a mat, and slide them down away from your ears. Focusing on the deep waist muscles, inhale and slowly move your knees to the right, then exhale and return to starting position. Repeat on the left; that’s 1 rep. Do 5–8 reps.
Start lying faceup on the mat. Lift head, shoulder blades, and feet off floor as you extend arms straight out. Neck should be relaxed, not strained. This is your hollow hold. Next, engage abs to lift chest towards legs as you bend knees so that body forms a V shape and shins are parallel to floor. Slowly lower back down to a hollow hold position and repeat.
Why it made the list: In our opinion, ab exercises with added resistance don't get enough love! They spur growth in the fast-twitch fibers like almost nothing else, and they can really build up the "bricks" of your six-pack. By adjusting the load, you can also train to failure at just about any rep target you want. A pin-loaded machine also works well when doing dropsets.