Weighted overhead crunch (on stability ball)

Sit on a stability ball with your feet flat on the ground and your knees bent at a 90-degree angle. Hold a weight plate or dumbbell with both hands and extend your arms overhead. Engage your abs and slowly curl your torso forward, bringing your chest towards your knees. Pause for a moment at the top, then slowly lower your torso back to the starting position. Repeat for the desired number of repetitions.