Swiss Ball Plank

The swiss ball plank places the hands on an exercise ball while the feet stay on the floor, and the instability underneath changes what the hold demands. A floor plank asks the abdominals to resist gravity pulling the hips down; add a ball and they must also resist the small, constant corrections it introduces in every direction. The shoulders work particularly hard here, because keeping the ball still requires continuous fine adjustment from the muscles around the joint. It is a genuine progression rather than a novelty, and it should follow a solid floor plank. The set ends when the hips start to sag or hitch upward, not when the timer says so, because a plank held with a collapsed lower back trains the opposite of what it was meant to. Rolling the ball in small circles raises the difficulty further.