The ‘Rated Perceived Exerion Scale (RPE)’ devised by the Swedish psychologist Gunnar Borg was devised to reflect the heart rate of exercise. It was unclear however whether the heart rate itself was an important physiological signal that told the brain how hard the exercise was. In this research atropine and practolol were used to modify the heart rate for a given exercise level and it was clear that the link between heart rate and the perceived level of exertion were not directly related.
Ergonomics. 1979 Oct;22(10):1141-6.