Borg RPE Scale: 6-20 vs CR10 Protocols, Heart Rate Correlation and Exercise Prescription
In short
The Borg Rating of Perceived Exertion (RPE) scale guides exercise prescription when heart rate is blunted by medications. Learn the 6-20 and CR10 protocols.
In this guide (4 sections)
What Is the Borg RPE Scale?
Developed by Gunnar Borg in 1962, the Borg Rating of Perceived Exertion (RPE) scale is an instrument for measuring how hard a person feels their body is working during physical exercise.
Perceived exertion integrates signals from peripheral working muscles, pulmonary ventilation, joint strain and central nervous system effort into a single conscious sensation.
Borg 6-20 Scale vs Borg Category-Ratio (CR10) Scale
Borg introduced two distinct scales designed for specific exercise monitoring contexts.
| Borg 6-20 Scale | Approx. Heart Rate (bpm) | CR10 Scale | Verbal Descriptor & Intensity | |
|---|---|---|---|---|
| 6 | 60 bpm | 0 | No exertion at all / Rest | |
| 7 to 8 | 70 to 80 bpm | 0.5 to 1 | Extremely light / Very light | |
| 9 to 10 | 90 to 100 bpm | 2 | Light (easy warm-up pace) | |
| 11 to 12 | 110 to 120 bpm | 3 | Moderate | |
| 13 to 14 | 130 to 140 bpm | 4 to 5 | Somewhat hard (aerobic conditioning target zone) | |
| 15 to 16 | 150 to 160 bpm | 6 to 7 | Hard / Heavy (lactate threshold vicinity) | |
| 17 to 18 | 170 to 180 bpm | 8 to 9 | Very hard (high-intensity interval training) | |
| 19 to 20 | 190 to 200 bpm | 10 | Extremely hard / Maximal exertion |
Heart Rate Linearity and Beta-Blocker Applications
The 6-20 scale was engineered so that multiplying the RPE score by 10 provides a rough estimate of actual heart rate in healthy young adults (e.g. RPE 13 * 10 = 130 bpm).
Clinical Significance in Cardiac and Pulmonary Rehab: Millions of cardiovascular and post-CABG patients take beta-blockers (such as metoprolol or bisoprolol) which blunt heart rate acceleration. In these patients, target heart rate formulas (like Karvonen formula) are inaccurate.
AACVPR guidelines mandate using the Borg RPE scale: maintaining patients between 11 and 14 on the 6-20 scale (or 3 to 5 on CR10) ensures safe, therapeutic cardiovascular conditioning without exceeding myocardial oxygen limits.
Frequently Asked Questions
Why does the Borg RPE scale start at 6 rather than 0?
Borg designed the 6-20 scale to mimic normal resting heart rates (60 beats per minute) up to maximal exercise heart rates (200 beats per minute) by multiplying the rating by 10.
When should a therapist choose CR10 over 6-20?
The CR10 scale is preferred when rating specific localized symptoms such as breathlessness (dyspnoea) in COPD patients or localized quadriceps muscle burning.
How do you prevent patients from guessing or giving social responses?
Instruct the patient to focus on their overall feeling of exertion rather than comparing themselves to others. Emphasize that there is no right or wrong number.
Related condition guides
Related recovery guides & articles
BookPhysio.in Editorial Team
The BookPhysio.in editorial team writes and maintains this content, checking it against reliable clinical sources. Content follows our medical review policy: general information only, and no page claims a clinical review until a named registered physiotherapist has signed it off.
Read our medical review policy