Hyperextension (exercise)

A hyperextension or back extension is an exercise that works the lower back as well as the mid and upper back, specifically the erector spinae.

It may be performed on the ground by lying prone with arms overhead and lifting the arms, upper torso, and legs as far as possible, or using a Roman chair to hold the feet down and hips up. Another version is the bird dog exercise, performed lying or the knees, where one arm and the opposite leg are lifted.

...
Wikipedia