A great exercise that targets your upper and lower abs. You will need an exercise mat and a weighted ball like a Ugi or cushioned medicine ball. For this demonstration I use an 8lb ugi ball that I purchased online for around $125 though I’ve seen other brands nowadays offering the same style ball for a LOT cheaper.
Lay flat on the mat holding the ball in your hands. As you raise your feet, pass the ball between your ankles and lower both your feet (now holding the ball) and your hands to the floor. DO NOT LET YOUR BACK ARCH OFF THE MAT. If this happens, lessen the distance you lower your arms and legs until your core is strong enough for you to do this without your back getting involved. Repeat this motion, passing the ball back-and-forth between your hands and legs.