This exercise increases power and strength throughout the core, specifically the obliques. The half-kneeling position is a slight variation to the standing kneeling rotational chop exercise.
Clip a rope attachment to the lowest level on a cable station machine. Begin by kneeling on the floor, with your outside knee (the knee farthest from the weight stack) bent 90 degrees. Keep this foot flat on the floor the entire time. Extend arms and grab the rope with an overhand grip, making sure that your hands are shoulder-width apart.
Brace core, squeeze glutes, and use your torso to pull the rope up and across your body, past your opposite shoulder. Return to the starting position.
Do not hyperextend your lower back, but concentrate on keeping a tall and straight spine.