Hollow Rock

The hollow rock is a staple of gymnastics conditioning and excruciatingly tough when performed correctly. To perform the hollow rock lay face up on the ground with your arms stretched overhead and legs out straight. Raise your arms and legs about one foot off of the floor and attempt to assume the shape of a rocker on a rocking chair, then gently, slowly, teeter back and forth.

The critical part of this movement is to pull the lordotic curve (lumbar arch) from the back so that the entire back is rounded from shoulders to butt. Initially, you will find that the rocking is rough because of a flat spot in the lower back. This is a perfect measure of both a weakness in and inability to innervate the lower abs.

The role of the hip flexors is fairly insignificant in the hollow rock but the role of the lower rectus (lower abs) is dramatic.  For many people the hollow rock is so hard that no matter how hard they try they “clunk” on each rocking as they come to level and the flat spot caused by insufficient lumbar flexion smacks the floor.  This “clunking” is a perfect measure of ones lack of lower ab recruitment.
                                                   
Activation, full recruitment, and development of the lower abs require enormous concentration and focus over months if not years.  The hollow rock is a near perfect tool to both test and develop low ab capacity.

Practice the hollow rock even if it gives you enormous difficulties. Start by trying to rock continuously for two minutes regardless of the quality of the movement.  Avoid raising the hands and feet to maintain the rocking motion as best you can.

When mastered, the body is dished out flat, the hands and feet are low, and the impetus for the rocking is nearly undetectable. When you can do this smoothly – no flat spot – for two minutes you’ll have the best abs in town.

- Crossfit Journal

Hollow Rock video demo.