hole saw bit

Most people have lost the ability to stabilize their pelvis and lumbar spine. This is a problem since the lower portion of the spine is anatomically designed to be stable; it functions best under low amounts of relative movement. Creating super-stiffness at the pillar is nonnegotiable if you're a lifter. It starts with positioning the pelvis and lumbar spine together synergistically. But achieving a position is vastly different than maintaining a position, especially when there's a heavy barbell on your back. That's where this movement comes in. It'll help you brace your core by creating tension in a controlled environment. You'll relearn what stability should actually feel like. – Dr. John Rusin