Positioned face down on a hyperextension bench with your hips supported, you lower your torso forward and raise it back up using the lower back, training the erector spinae along with the glutes and hamstrings.
The hyperextension, or back extension, is one of the most valuable low-cost movements in the gym: it trains the spinal erectors, glutes, and hamstrings through a hinge without a bar on your back or in your hands. Program 3 to 4 sets of 10 to 20 reps at the end of a leg or pull day, or use lighter sets as a warm up before deadlifts. It is the safest place to build the back endurance heavy squats and pulls demand.
You can steer the emphasis with setup. Rounding the upper back slightly and squeezing the glutes at the top turns it into a glute exercise; keeping a neutral spine and thinking about lifting the chest biases the erectors and hamstrings. Progress by holding a plate to the chest in jumps of 2.5 to 5 kg, and control the lowering rather than diving toward the floor. Despite the name, there is no need to hyperextend: a straight line from head to heel is the right top position.
Done with control and sensible loading, they are one of the best things you can do for it. Problems come from swinging aggressively past neutral at the top with added weight, not from the movement itself.
Either can be correct depending on your goal. For glutes, tuck the pelvis slightly and squeeze hard at the top; if you feel only lower back, the pad is likely too high, so drop it below the hip crease so the hips can hinge freely.
The 45 degree version is hardest near the bottom and easier at the top, while the horizontal version is hardest at the top. Both build the posterior chain well, so use whichever your gym has and train it through a full range.
Log your hyperextension sets in 1RM.fit and watch your estimated 1RM update automatically as you get stronger.