Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance

by Alex Hutchinson

The system Marcora used to measure perceived exertion was called the Borg Scale, named for Swedish psychologist Gunnar Borg, who pioneered its use in the 1960s. Though there are many variations, Borg’s original scale ran from 6 (“no effort at all”) to a maximum of 20 (the penultimate value, 19, was defined as “very, very hard”), with the numbers corresponding very roughly to your expected heart rate divided by ten. A Borg score of 13 to 14, for example, corresponds to an effort you’d call “somewhat hard,” which would produce a heart rate of 130 to 140 beats per minute in most people. But Borg viewed the effort scale as far more than a convenient shortcut for researchers whose heart-rate monitor ran out of batteries. “In my opinion,” he wrote, “perceived exertion is the single best indicator of the degree of physical strain,” since it integrates information from muscles and joints, the cardiovascular and respiratory systems, and the central nervous system.4 In his talk at the conference in Bathurst, Marcora took this argument a step further. Perceived exertion—what we’ll refer to in this book as your sense of effort—isn’t just a proxy for what’s going on in the rest of your body, he argued. It’s the final arbiter, the only thing that matters. If the effort feels easy, you can go faster; if it feels too hard, you stop. That may sound obvious, or even tautological, but it’s a profound statement—because, as we’ll discover, there are lots of ways you can alter your sense of eff...