This is a classical exercise with emphasis on the abdominal internal oblique muscle.
Lie down on one side with one extended hand placed on the floor.
Place your arm strictly under the shoulder to avoid injuries.
Bend one leg, press the other one to the floor. Pull in your abdomen.
Your body should be in one line. Don't bend your back.
As you exhale, slowly raise your hip so that it forms one line with your body.
Pause for 2-3 seconds at the top.
As you inhale, slowly return to the starting position.
Don't push your pelvis back during the exercise.
Don't swing your body and do the exercise slowly.