Most of us are familiar with the 1-10 scale of RPE where 1 is complete rest and 10 is maximal (and unsustainable) exertion. This is used by most personal trainers and sports coaches to ensure that their participants are working at the correct intensities to attain the desired training adaptations. 

In the case of personal trainers, especially those working with exercise prescriptions, is that lower RPEs are more suitable and safer for participants in the moderate or high-risk categories for a cardiac event. Maybe don’t make your grandmother do burpees. 

If you’re not familiar with RPE, or any other scientific jargon mentioned in this blog entry, click here to view the glossary page.

How do we measure RPE? 

It’s simple, we just ask the participant. It’s usually worth explaining the 6-20 range of the Borg scale to athletes or participants that likely aren’t familiar with it yet

Why does the Borg scale go from 6-20?

This is to correlate with heart rate. 

A resting heart rate between 60 and 100bpm is classed as healthy, depending on the individual. When working with a sporting population, we can expect to see closer to that lower figure of 60 heartbeats per minute. We can make a crude estimate of an individual’s maximum heart rate with the following formula:

220 - (Participant age) = Maximum Heart Rate (HRMax)

This gives a 20-year-old football player a theoretical maximum heart rate of 200bpm and a 30-year–old rower a HRMax of 190bpm. 

Multiply the Borg scale RPE measurement by 10 and it should be pretty close to the participant's heart rate. The bottom of the Borg scale is 6 would thus be 60bpm. , which is a state of total rest. The maximum is 20, which would be 200bpm. 

Of course, in a physiology lab, we’re usually strapping a heart rate monitor onto the participant anyway. This leaves less room for error than the Borg scale estimate. 

If we know heart rate, why use RPE? 

As mentioned, the Borg scale correlating with heart rate is neat. However, we usually have a more accurate HR measurement from a chest strap when conducting a VO2Max or similar test.

A few other uses remain for RPE, however. One example is to make sure we’re not straining the participant too hard, or at least not doing so too early. Even in the case of a VO2 Max test, which is a maximal exercise test, we don’t throw the participant in at the deep end. The participant's exertion is increased incrementally so that the relevant physiological mechanisms have time to activate (e.g. cardiac output increase, vasodilation, etc.)

We can also compare RPE to an athlete’s output (e.g. Wattage on a bike) to measure the effects of psychological factors (motivation, mood, sleep, etc.) or supplements (caffeine, taurine, etc.) on the perceived difficulty of an exercise. Follow the example below:

• Athlete A was given a placebo “energy drink” without any caffeine. While putting out 180W on a stationary bike, he states his RPE as 14.

• Athlete B has been given a fair dosage of caffeine in an energy drink. While also putting out 180W on a stationary bike, he states his RPE as only 12. 

Assuming the athletes are equally trained, then the actual exercise intensity is equal, but their perceptions are varied. If that pattern is repeated across a sufficiently large sample size then it could be concluded that caffeine decreases perceptions of exercise difficulty during sub-maximal exercise. 

Of course, that’s just an example. 

Conclusion

The Borg scale certainly has its uses. Even if we know heart rate and more, the 6-20 scale allows for a greater degree of accuracy with its 15 different points than the standard 1-10 scale does with 10 points. 

Measuring RPE also makes many exercise tests safer. If a participant is finding a particular exercise intensity much more strenuous than expected, it may be a sign of something wrong physiologically or with the procedure itself.

In the case of a VO2 max test, we can determine that maximal effort was achieved by observing other physiological measurements heart rate (did it approach the individual theoretical maximum?), respiratory exchange ratio (Co2 Expired compared to Oxygen used) and blood lactate levels.