Definition
The plane that divides the body into upper and lower halves, containing every rotational movement.
Also called the horizontal plane. Internal and external rotation of the shoulder and hip live here, as do cable chops, Russian twists, med-ball throws, and the rotation of a golf or tennis swing.
Most transverse work in the gym is anti-rotation rather than rotation: a Pallof press asks the torso to refuse to turn against a cable, which is what the trunk actually does when a client carries something heavy on one side.
Program it in seconds, not reps. Three sets of 20 seconds per side on a Pallof press, with a load light enough that the arms stay locked out, does more for trunk control than 30 twists with a plate.