Simple exercise for abdominal muscles.
Sit on the floor, with you legs straight or slightly bent, keep thighs together.
Keep your back straight and hold your arms to the sides parallel to the floor.
As you exhale twist your torso on the left (or on the right). Keep your neck, arms and upper back stationary.
As you inhale return to the starting position.
Don't move your shoulders, keep your arms parallel to the floor and twist to the other side.
Twist is forbidden for people with spine injuries.
To increase the load, you can take additional weight (a dumbbell, a barbell plate or a ball) and raise your legs above the floor. Keep your knees slightly bent.