Schwartz's key postulation centers around Type IIa fibers. Type IIa fibers produce energy and sustained power -- say the kind a runner would need during the final 400 meters of a mile -- but because they rely on oxygen, not glucose, to produce energy, they are more resistant to fatigue. Furthermore, Schwartz discovered that, through training, Type IIb fibers can be converted to Type IIa fibers, allowing an athlete to fight off fatigue even longer.
But how to accomplish that? Schwartz had an idea. He called it critical velocity (CV) training. Schwartz calculated that the CV pace -- which he calculated to be 90% of a runner's VO2 max -- was the perfect pace to train at to develop Type IIa fibers. According to Schwartz, at that pace Type IIb fibers can be transformed into Type IIa fibers, which will become stronger and more efficient at using oxygen to produce energy. Go faster than CV pace and fatigue builds up too quickly in the muscles. Go slower and you start working the Type I fibers instead of the Type II fibers.
"[CV pace] is the hub, thatâ€™s the fulcrum," Schwartz said. "I put training on either side of it for other purposes. To be a multidimensional runner, you have to have some speed, youâ€™ve got to have some generalized aerobic endurance. But if you focus on the CV, which I call the center point of the stamina range, everything else will fall into place."
You train properly and see where that takes you, you don't force it.
"Iâ€™m not trying to rush people into top fitness by hammering them with VO2 max or so-called 'goal pace' training, which has really no physiological foundation," Schwartz said. "Our body's only where it is right now. But humans think, 'If I just run at goal pace, I'll automatically get there.' Um, that's not how your body develops. There's no physiological basis for that.