Setup

Lie on your back with your legs straight and your arms by your sides. Lift your head and shoulders slightly off the floor before the first rep and keep them there. Nothing else to set up — watch the video, the movement is easier to see than to read.

Why the setup does the work here

The small lift at the start switches your stomach on before you move. If your shoulders rest on the floor, your legs and hips take over and your abs just go along for the ride. Start lifted, stay lifted, and the muscle works the whole set.

Technique

Raise one leg, knee slightly bent, and at the same time crunch up and clap your hands together underneath that leg. Lower the leg and your upper body back down, then do the same with the other leg. Keep alternating at a moderate, steady pace — up, touch, down, other side. Breathe out each time you come up, and don't let your head drop and rest between reps.

Why technique decides everything here

Both ends of your body move toward each other here, and that's the point. The leg comes up, the chest comes up, and your stomach shortens from the top and the bottom at once. If you only lift the leg and leave your shoulders down, the hip does the work. If you only crunch and leave the leg low, you're back to a normal crunch. The hand clap under the leg is your checkpoint — if your hands meet, both halves did their job.

Common Mistakes

Reaching with the arms while the shoulders stay flat on the floor — the hands touch but nothing worked. Dropping the head down to rest after every rep, which breaks the tension. Rushing, so the legs swing instead of lift. And bending the knee too much, which turns it into a small, easy movement.

Where people lose results

This one looks light, so people speed it up and count instead of feeling it. Keep the tempo moderate, keep your shoulders off the floor from the first rep to the last, and stop the set when your form breaks — not when you hit a number.