The RPE Scale is one of the most widely used methods used to measure ride effort requires the person performing the physical work to answer a question about perceived effort.

Gunnar Borg was a psychophysiologist studying the effects of physical work and devised a scale that had verbal expressions allowing someone to point to a number between 6 and 20 that represented the total pain or effort they were perceiving.

He later invented the CR10 scale which is still in widespread use today, especially in clinical & lab tests, and in speed & power sports. There is a variation, introduced by Dr Carl Foster that multiplies the effort rating by time to get a ‘Session RPE’