Position yourself on the back extension machine with your hips on top of the cushioned pads and your feet secured under the leg anchor.
Place your arms behind your head, or hold onto a kettlebell (10 pounds is a good starting point) with your arms fully extended.
Lift your torso up a few inches and squeeze your gluteal muscles for two seconds. Then, lower your torso back down to the starting position. Be sure not to overextend your back.
This counts as one rep.
If you're a beginner, perform this exercise without weight or start with a light weight. As you feel comfortable, begin to add or increase the weight.