Place a stability ball under your hips and lower abdomen, hold a weight plate or dumbbell against your chest, hinge at the hips to lower your torso toward the floor, then extend your back to raise your torso until your body forms a straight line. Keep your core tight and move in a controlled manner.
Log your weighted hyperextension (on stability ball) sets in 1RM.fit and watch your estimated 1RM update automatically as you get stronger.