Scott Semple is correct. There is no science or study behind this. It comes from, and is supported by, empirical observations made over decades on hundreds or even thousands of athletes.

As I mention in the article, when the first Polar wearable HR monitors became available (got mine in 1982), coaches and athletes began to notice that in extended runs their HRs tended to drift upward in the later stages of the run even if they were holding a constant pace. More interesting was that the higher the pace, the more the HR drift.

The same can be said for the 10% rule that we espouse here.

Bear in mind something that I have said in several places on this site and our books: By a large margin, coaches tend to lead the way (over the sports scientists) when it comes to discovering effective training tools. When you have thousands of coaches and millions of guinea pig athletes over several decades the best practices float to the top. This occurs through an evolutionary process of trial and error, hypothesizing and testing ideas in the ultimate laboratory that is competition. Years later a study comes along and “prove” what coaches have known all along.

I hope this helps.
Scott