What is the “stir the pot” plank exercise? Perform a forearm plank with your elbows supported on a stability ball, also known as a Swiss ball, and the balls of your feet resting on the ground.

The plank exercise represents one of the most effective ... requiring continuous core engagement to maintain body alignment. Variations like decline push-ups (feet elevated) increase the abdominal ...

you could put your toes on a tree and do a decline plank, or you could put your hands on a park bench and do an incline plank. No doubt, the standard, straight-arm high plank is a great exercise.