Any compelling proof I need for the science of P90X is in the Great Wall of China. I cajoled Gordon Laurie, British jujitsu enthusiast and Washington-Lee High
School's Assistant Principal in Arlington, Virginia to take the difficult route along the Wall in the hour or two we had to engage this once-in-a-lifetime experience.
553 steps. That is how many steps I lasted. Taking off at a brisk climb, I began to slow down within 100 steps, taking generous breaks every fifteen or twenty thereafter. By the time I had scaled the first two levels, my triceps (of all muscles) were given over to involuntary spasms, and the innermost part of my vital organs felt like I had been wrestling 10 minutes past the 3-minute limit. 
I sat down by a tower on the second tier to catch my breath. But my breath never came. It wasn't my breath. It was my life. I felt dried inside. My muscles had rebelled and were doing silly jigs that would have made me laugh had laughter even been a recollection of my human experience at that point.Gordon Laurie, empathized with me for a few minutes, recovered, and proceeded to the next tier. Watching him climb, getting smaller and smaller, almost made me retch. I had been a gymnast for well over 25 years, lifted weights, yada yada. So what was my problem?As best as I can understand, controlled, organized workouts in air-conditioned gyms isn't a value system that works on the Great Wall of China. My pommel horse routine just didn't come in handy for the duration of my climb. I might have somewhat been prepared were I to have worked out on a pommel horse that constantly and randomly changed angles as I executed circles and scissors. Or I might have been prepared were I to have run laps on a track that randomly changed shape, inclining and declining unpredictably. 
I noticed that the creators of the Great Wall used series of uneven steps. Sometime they were steep. Then they would be cut in half. Then they would only be a few inches high but long. Whatever the case, the rhythm was uneven and disallowed your body to strike a projected stride. That didn't include the non steps that still sloped upwards at a deceptively steep incline. I have 17 steps in my house from the first to the second floor. What I climbed was almost 33 stories of uneven, muscle-punishing steps. So if anyone wants to criticize P90X, I suggest you consider the angle. Literally. 
