Grab the handle of a cable that has a low attachment, about ankle level with your right hand. Stand tall with your cable at your right side with your feet about shoulder-width apart. Stand far enough away from the cable so that it's at roughly a 45-degree angle to the floor.
Without rotating your body, bend your torso sideways to the right until you feel a mild stretch in the left side of your torso. Reverse the action and finish the rep by slightly flexing your torso to the left against the resistance.
There's not much resistance when you're standing upright holding a dumbbell because the dumbbell is very close to your body, giving you a huge mechanical advantage over the weight. But when doing them with a cable the angle of the cable forces you to work hard to stay upright and maintain that position between reps, giving you more time under tension through the range of motion.