One of my personal challenges in physical activities (martial arts, Yoga, weightlifting) has always been flexibility. Some people have quite naturally good flexibility, others have to work on it. What exactly is flexibility? There is a very common perception that flexibility is a physical characteristic - that its a question of muscle, ligament and tendon length. Stretching exercises, therefore, are thought to result in physical lengthening of the body parts resulting in increased flexibility. Numerous authorities have a radically different view on this. Tom Kurz, Pavel Tsatsouline and even a professor of kinesiology at UC Chico (Duane Knudsen - see this recent NYTimes article) have very changed perspectives about flexibility and stretching. Their thinking is that flexibility is not a physical restriction - that is, you are not limited by the length of your muscles or ligaments or tendons - but rather by the programming of your nervous system, which is not under your conscious control. While under anesthetic, for example, a surgeon can rotate your shoulder a full 360 degrees. An experiment used by both Tom Kurz and Pavel Tsatsouline using the side splits is to lift one leg at a time into the splits position, like the photo below illustrates: If you can do this with each leg, you have shown that it is not a physical restriction that prevents you from doing the full side splits. There is no tissue connecting each leg to one another, which means that something else is stopping you from performing the splits. That "something else" is your nervous system. The theory is that your unconscious nervous system imposes these restrictions on how far it will let you stretch your muscles. Flexibility training, then, should concern itself with reprogramming the nervous system to let you stretch further. This is precisely what the programs of Tom Kurz and Pavel Tsatsouline are concerned with. For some free information on the kinds of stretching programs (typically known as "dynamic stretches") I recommend Tom Kurz's free column, "Stretch Yourself". Good luck with your training!

Niall O'Higgins is an author and software developer. He wrote the O'Reilly book MongoDB and Python. He also develops Strider Open Source Continuous Deployment and offers full-stack consulting services at FrozenRidge.co.