Place a kettlebell on its side, on the floor by your side. Come down on to the floor in a plank position. With your elbows in-line with your shoulders and your feet approximately hip width apart or slightly wider. Grasping hold of the kettlebell handle, move it forward and back, lengthening and bending the arm. Throughout the movement keep your core braced so that your body does not twist or move. Perform the saw motion for the desired number of repetitions, then repeat on the other side. Works the obliques, abs, and lower back muscles

High plank with shoulder taps. Hold for 3 seconds or more to increase the intensity.

If regression is needed, you can do this lying on the ground.