A PVC pipe across your back to open the sides of your torso.
Keep your hips facing forward, do not lean back or rotate as you bend.
The pipe across your upper back keeps your posture honest while you bend sideways, so the stretch runs cleanly down one side of your trunk while the opposite side's core controls the descent and pulls you back up. Working one side at a time makes asymmetries obvious. It earns its place opening up the lateral trunk before squats, overhead work or rotational training, where a stiff side quietly steals range.
It keeps your shoulders and upper back set so you bend purely sideways instead of slumping forward. Losing the pipe's position is your signal the rep went wrong.
Brace lightly and think about sliding your torso along a wall directly to the side. If your hips shoot the opposite way or you rotate, shorten the bend.
A bit of both. The bend stretches the side you lean away from while the other side works to control it, which is why slow reps beat hanging out at the bottom.
