The sigma training concept is not new @ all. Actually, it is quite old, ancient even. It is the concept of holism, but applied specifically to physical training. When analyzing a training program of any kind, we must look @ the whole system, the totality of circumstances to understand the synergy between seemingly isolated components to get the best results from the integrated system.
In mathematics, sigma notation is used to represent the summation of many similar terms. For our general purpose, it is the summation of countless physical endeavors in the pursuit for mastery of the human form. In a fitness sense, it is well researched & documented that we get much better results & athletic performance when we train the body as one cohesive unit, with all of your muscles working together like a team, instead of as individual components working in isolation. From a combatives perspective, it is learning & practicing in the different modes of combat (grappling, striking, weaponry) together in an integrated manner so there is no hesitation to adapt to the conditions of the fight. Whereas most fighters need to "switch gears" every time the fight changes.
It is this summation, this teamwork that allows us, as a group, to accomplish much greater things than any individual is capable of alone.