Lay torso and waist on bench and grasp handles. Feet should be above floor with legs straight.
Raise legs by extending hips as high as possible until legs are nearly straight. Lower legs to original position. Repeat.
Also see Reverse Hyper-extension performed with exercise ball on bench.
If knees are bent significantly, hamstrings are not involved. Consider regular hyper-extensions or other bodyweight glute exercises.
Exercise can be made more challenging with additional weight. Some individuals may be able to articulate both through the hips and through the lower back (ie: lumbar spine), in which case, Erector Spinae also becomes synergist.