Weighted Reverse Crunch

Lie on your back with a dumbbell held between your feet or ankles and your knees bent toward your chest. Curl your hips off the floor by drawing your knees up and in, rather than swinging your legs, so the movement comes from your lower abs shortening rather than momentum. Your shoulders and arms stay flat on the floor for support throughout — this version moves your pelvis, not your upper back. Lower back down slowly until your hips just touch the floor before curling up again. The dumbbell adds resistance right at the end range where a reverse crunch is usually weakest, so keep the motion small and controlled rather than kicking your legs to build momentum.