Begin in a forearm plank position with your shins resting on a stability ball and your elbows directly beneath your shoulders. Brace your core and keep your body in a straight line from head to heels. Slowly push your forearms forward, allowing the ball to roll slightly backward under your shins. Use your core muscles to pull your body back into the starting plank position in a controlled motion. That forward and backward “sawing” movement increases demand on your abs and stabilizers throughout.
Log your exercise ball body saw sets in 1RM.fit and watch your estimated 1RM update automatically as you get stronger.