Get into a plank position with a hand on each dumbbell instead of the floor, feet set wide for a stable base, body in a straight line from head to heels. Row one dumbbell up toward your hip while pressing the other down hard into the floor to keep your hips from twisting. Set that dumbbell back down under control, then switch sides. The real work is resisting rotation, not the rowing itself; if your hips swing open every time you pull, the plank is breaking down before your back gets a proper row in.