Grab a flat bench and position it in front of a cable machine.
Attach a hammer grip to the low pulley cable and select the weight you want to use on the stack.
Sit down on the bench facing the cable machine with your feet and knees together.
Grasp hammer grip extension from below with a neutral grip.
Sit straight up with your shoulders back and arms fully extended. This is the starting position.
Slowly pull the grip towards your lower waist and keep your chest curled up whilst your lower back pushes out the opposite way.
On the movement back to the starting position use a slow contraction whilst stretching your shoulders forward right at the end to maximise stretch of the back.