Russian Twist
Start by sitting on the floor, with your knees bent and heels on the ground.
Lean back so your upper body is at a 45-degree angle to the floor. Keep your chest up with a neutral spine, maintain this V-shape throughout the whole exercise. Link your hands together in front of your chest, draw in your abdomen . Rotate your torso and arms to one side do not try to twist excessively , then do the same in the other direction . Comparing the movement to hands on a clock you would keep movement to 10 and 2. . Count that as 1 repetition.
To increase difficulty lift your feet off the ground.
Used as a strength exercise to target the internal/external obliques, rectus abdominus and transverse abdominis. Try doing 2-3 sets of 10-24 repetitions in addition to 1 or 2 other abdominal exercises 2-3 times per week.