Sit on the floor, upper body leaning slightly back, legs bent (heels on the floor or slightly raised), arms bent and hands clasped in front of the chest; rotate the upper body in a controlled manner to the left and right (optionally, touch the floor with your hands at hip height). Aim: controlled trunk rotation whilst maintaining a stable core. Important: The rotation comes from the core, not from the arms.
Attention:
Hunching instead of a stable core posture, momentum instead of controlled rotation, excessive range of motion without control, hips not moving with the body (no isolated rotation), feet hanging loosely without tension (in the advanced version), breath not held.
Lighten:
Keep your feet on the ground; keep your upper body more upright (less forward lean); slower, smaller rotation; keep your heels in place (e.g. by tucking them under something).
Harden:
Add weight to your hands; perform the eccentric phase slowly (deliberately rotating back); hold the position at the end of the rotation (isometric hold); use a longer lever arm (arms straight rather than bent); use an unstable surface under your bottom (e.g. a balance pad).
