The following are some excerpts from the CrossFit Journal.

Our use of the term “gymnastics” not only includes the traditional competitive sport that we’ve seen on TV but all activities like climbing, yoga, calisthenics, and dance where the aim is body control. It is within this realm of activities that we can develop extraordinary strength (especially upper body and trunk), flexibility, coordination, balance, agility, and accuracy. In fact, the traditional gymnast has no peer in terms of development of these skills.

The barrier to participation in gymnastics is twofold. The first difficulty is scaling load. Imagine if the only load available in gyms were bodyweight loads. What would that do to the popularity of weight training? It would close nearly every gym in the world. There would be as many people lifting weights as there are doing gymnastics – damned few.

The second barrier to gymnastics participation is less apparent to most athletes and coaches but every bit the impediment that scalability is. Gymnastics movements at every level require extraordinary body control. Weight training is to gymnastics as the tambourine is to the violin. Weak mindedness manifested as a low tolerance for frustration culls the herd.

With proper scaling and consistent practice, basic gymnastic skills can and should be learned. The rewards far outweigh the frustration of a few clumsy failed efforts. Here is one of the most basic gymnastics positions and exercises. It is difficult at first, but well worth your practice time to learn.

The Hollow
In a hollow a gymnasts hips are turned under, legs are tight chest rounded inward. Lie on your back on the floor with your arms by your ears. Lift your legs slightly off the ground. Lift your head slightly off the floor. Your lower back should maintain contact with the floor. See video.

The Hollow Rock
A seemingly innocuous little exercise, 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. (Recent evidence suggests that the obliques play a major role in lumbar flexion http://www.pponline.co.uk/encyc/0689.htm)

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.

Lower ab recruitment is the toughest part of ab training and never well developed by most athletes. It is so common as to be a visual clichŽ that the aerobics instructor who teaches “ab classes” at your local gym can do thousands of crunches but still has a lower abdominal pooch as though three months pregnant.

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.

You can practice the innervation/recruitment required to engage the lower abs/flex the lumbar spine and perform the hollow rock by standing with your back, feet, and head against the wall and pressing hard against the wall at the shoulders and slowly rolling the contact point from the shoulders down to the mid-back, down to the lumbar spine and ending with the butt pushed hard against the wall. You will notice that making hard contact with the wall through the region of the low back is exceedingly hard and requires an anterior to posterior roll of the pelvis and deep low ab contraction. You can test the contact by having someone place a rolled up magazine in the region of the lumbar curve while you try to pinch it against the wall as they attempt to slide it out. Done right, this produces a distinctive pulling above the pubic bone. That’s your lower abs working. Repeating this ten times is a great low ab conditioning drill.

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.