Lie flat on your back with your arms extended over your head and an exercise ball gripped firmly between your ankles. Simultaneously lift your arms and legs to meet in the middle, creating a "V" shape with your body, and transfer the ball from your legs to your hands. Lower your limbs back toward the floor while keeping the ball in your hands—stopping just before your hands or feet touch the ground to maintain tension—then repeat the motion to pass the ball back to your ankles. This movement is a powerhouse for the entire core, as it forces the upper and lower abdominals to work in coordination while the long levers of your limbs provide intense resistance.