A classic exercise to work the abs.
Lie down on a bench with your legs stretched out.
Place your hands by your sides holding on to the bench.
As you exhale, slowly raise your legs, extended straight as possible with your knees, until they get a 90-degree angle with the floor .
Pause for 1-2 seconds at the top and, as you inhale, slowly return to the starting position.
Start performing the exercise by raising your knees to your chest. It's an easier variation.
Don't swing your body and don't jerk up your legs.
If you have problems with your lower back, this exercise can cause back pain.