Lean and reach to chisel the side waist.
Bend only sideways, never forward or back. Keep the motion slow and controlled.
Bending sideways at the waist and pulling yourself back upright works the muscles along the side of your trunk through a plane most training completely skips. The strict sideways path is what keeps the work where it belongs, drift forward or backward and the movement dilutes instantly. Done slowly, it builds the side of your core that planks alone never shorten and lengthen.
They train the muscles along the side of your trunk, they do not burn fat off that spot. Do them to build a stronger, more capable core, and let overall training and nutrition decide how your waist looks.
Master the bodyweight version first, slow and strictly sideways. Once that is easy, holding a weight in one hand at a time is the natural progression, working the opposite side as it pulls you back up.
Leaning forward or back turns the movement into a vague torso wobble and takes the tension off the side of your core. Imagine sliding between two panes of glass, purely sideways, slow both directions.
