Lie face down on a stability ball with your hips supported on top of the ball and your hands on the floor for balance. Keep your legs extended straight behind you with your toes lightly touching or hovering above the ground. Engage your core and squeeze your glutes to lift both legs upward and slightly backward in a controlled motion until they reach roughly in line with your torso. Avoid swinging or using momentum. Pause briefly at the top while squeezing your glutes, then slowly lower your legs back down under control to the starting position and repeat.
Log your reverse hyperextension on stability ball sets in 1RM.fit and watch your estimated 1RM update automatically as you get stronger.