The Rate of Perceived Exertion (RPE) scale is a numerical value system used to express how hard somebody feels they are working during exercise. The Swedish researcher Gunnar Borg invented it in the 1960s and it’s been widely used in strength and weight training ever since. But what is it?

“I know it’s because of the 4x4s, that’s definitely what did it” they told me. Um, was it? Are you sure it wasn’t one of the many other training facets we’ve been working on? “What about the interval boulders, those seemed to really suit you well?” I asked.