I first heard of the idea from Renato Canova, the running coach for more world records, World Championship and Olympic medals for distances between 800m and the marathon than any coach in history. After hearing this I dug into the data for many of the top athletes I coached including all my old tests. Sure enough I found that top athletes had AeT to AnT spreads in the range if 5-8% and that the lower performing, less well trained and younger athletes had spreads over 10% and cases of ADS even as much as 30%. I like Canova found that when I decreased this spread before adding much intensity I got better performance results than if I tried the opposite.
Most amateurs will need to be training seriously to even attain the 10% spread and so it seems like a sensible upper limit and it has proven attainable and effect with hundreds of folks.
This concept is simply a mathematical manifestation of the main underlying principle of all the training you read about in our books and in mainstream endurance training: The aerobic base is THE critical component to maximizing endurance gains. The bigger that aerobic base (in this case AeT is the proxy for that base) the bigger the potential endurance gains for the athlete can be. As its name implies, this BASE provides the support for the high intensity work needed to improve endurance. The bigger the base them event specific workouts (which tend to be high intensity) the athlete can handle without significant reduction in this aerobic base. Too much intensity on top of too small a base will will decrease the base.
This, like most of of the methodologies common in endurance sports did not come from a “study”. History shows that coaches lead the scientists in discovering what in training works and what does not. The thousands of coaches and millions of athletes over decades trying and either adopting, modifying or rejecting training methods is the biggest lab study ever conducted. This empirical trial and error evolution will eventually float the best ideas to the top. Sometimes exercise scientists come along later and discover some underlying physiological rationale for why these ideas work but I can’t think of a case where the science came before the coaching practice.
Scott
