Decline sit-ups are an effective core exercise that increases the difficulty of a standard sit-up by using a decline bench. This exercise targets the abdominal muscles more intensely, improving strength and endurance.

1. Lie on a decline bench with your feet secured under the foot pads.
2. Place your hands behind your head or cross them over your chest.
3. Engage your core and lift your upper body towards your knees.
4. Slowly lower your upper body back to the starting position.