An important concept in mind-body exercises like yoga and just about any martial arts is Chi, or Qi.
I have to give the late Stan Rossi a lot of credit for radically transforming my understanding of Chi. It was a long long long path, frought with a healthy dash of skepticism that was released without hesitation after one class with Stan.

To explain what happened I have to go through many years of training and discussions. I first heard of Chi from a judo instructor I worked with. He called it by it's Japanese name, Ki. I asked him what Ki was and he said, "let me show you". He reached out his finger and held it two inches from my forhead. I felt a touch, even though he never touched me. It was like magic!
I later learned from Mister Ho that Chi is an essential life force that flows through the body. He said there were channels in the body that followed (though not exactly) the blood circulatory system. Tai Chi moves this force around and projects it outwards. This force can heal your body, and be used as a devastating weapon by martial artists.
Yet even as I watched people use this to bend rebarb, even when I could muster chi to take pointy sticks in the soft part of my neck, I still was skeptical. I thought it was some trick, or a combination of physical mechanics. In fact, I spent quite a bit of time wondering what it was.
And while I was in Dallas, I remembered Stan Rossi coming to practice with us. He was a student then, with no students of his own, but he said something quite profound. "to master chi, you first have to believe in it." I smiled and listened, but inside I was sooooooo skeptical. I pictured him as one of those goofy new age philosophers and almost forgot him entirely.
Then about ten years later, I am in his class in Austin. I had come to believe something was going on because my Chen lessons had reached a point where I could feel something, particularly in the holding column position that Stan was practicing that night.
We were in a circle, and I felt the chi between my hands stronger than ever. In fact, it was hard to push my hands together. I could feel it bouncing back and forth. Stan was walking around the circle, helping students whith their form, when I turned my hands towards the center of the circle, sending the chi in his direction.
He turned around immediately. Understand now, he had no normal cue what was going on with me. If you saw a film I would have just tuned my hands a little. There was no noise, only a subtle movement that Stan detected as surely as if I had turned a fan on him. He walked over, looked between my hands, where I could feel this strong field, and passed his hands between mine in an exploratory manner.
From then on, I was a believer in Chi.
Chi and Prana
Lately I have been fascinated by the connections between Yoga and martial arts. The study of this life force is very similar. In fact, they were probably originally developed in ancient India and enhanced and changed in ancient China. However my understanding of both systems is in it's infancy, so take my comparisons as speculation at best.
Yogi's call this life force Prana, and as near as I can determine they are discussing the exact same thing. However, I think Yoga practitioners manipulate and enhance Prana in very different ways from how martial artists use and enhance Chi.
Both disciplines use breath control. Both encourage different types of breathing. Both stress the immense importance of Chi (Prana) for health and long life.
Martial artists usually accompany Chi exercises with great sweeping movements of the body. They can focus Chi in different parts of their body. They can even send it into other things, like a sword or an opponent. One practice I have seen many times is people relaxing their arm and filling it with Chi...the arm cannot be bent.
Yogi's, to my knowledge, only focus on the health aspects. When I spoke with one yoga teacher about moving Prana she winced and said "do you want to move it?" It made me think about how Yogi's observe the flow of Prana while martial artists seek to control Chi and utilize it.