Borg Rating of Perceived Exertion (RPE): 6–20 Scale vs. CR10 Scale, Physiological Correlation, and Cardiopulmonary Rehab

The Borg Rating of Perceived Exertion (RPE) is a validated psychophysical measurement scale developed by Swedish psychologist Gunnar Borg to quantify an individual’s subjective perception of physical effort, cardiorespiratory strain, and muscular fatigue during exercise or physical work. In clinical exercise physiology, cardiopulmonary rehabilitation, occupational ergonomics, and interventional clinical trials, the Borg scale integrates peripheral muscular feedback (lactate accumulation, mechanoreceptor strain) and central cardiorespiratory signals (minute ventilation, heart rate, oxygen uptake) into a single numerical score.

Clinicians and clinical researchers use two distinct instruments created by Gunnar Borg—the Original Borg 6–20 RPE Category Scale (designed to scale linearly with heart rate and oxygen consumption) and the Borg CR10 (0–10 Category-Ratio) Scale (designed to capture nonlinear symptom intensity such as dyspnea or localized angina)—alongside objective functional assessments and validated physical activity questionnaires.

What Is the Borg Rating of Perceived Exertion and How Is It Used in Clinical Research and Healthcare?

First introduced by Gunnar Borg in the 1960s and formalized in his landmark 1982 paper in Medicine and Science in Sports and Exercise, perceived exertion reflects the gestalt of physiological sensations arising from working skeletal muscles, joints, the cardiovascular system, and pulmonary ventilation. Rather than relying solely on external workload (watts on a cycle ergometer or treadmill speed/grade), the Borg RPE measures the internal physiological strain experienced by the patient.

1. The Original Borg 6–20 RPE Category Scale

The classic Borg RPE scale is a 15-grade equidistant interval scale ranging from 6 to 20, with verbal anchors assigned to every odd integer (and 6 and 20). Borg constructed the 6–20 numerical range so that, in healthy young-to-middle-aged adults performing dynamic large-muscle aerobic exercise, multiplying the RPE value by 10 approximates the individual’s steady-state heart rate in beats per minute (HR ≈ RPE × 10, spanning roughly 60 bpm at rest to 200 bpm at maximal exertion):

Borg 6–20 RPE Score	Standard Verbal Anchor	Approximate % Heart Rate Reserve (%HRR) / %VO2max	Clinical Exercise Intensity Zone (ACSM / AACVPR)
6	No exertion at all	< 20%	Resting baseline (seated or standing quiet rest)
7 – 8	7 = Extremely light	20% – 29%	Very light warm-up / early inpatient mobilization
9 – 10	9 = Very light	30% – 39%	Light intensity (comfortable walking, Phase I inpatient cardiac rehab)
11 – 12	11 = Light	40% – 59%	Moderate intensity lower range (target entry zone for Phase II outpatient cardiac rehab)
13 – 14	13 = Somewhat hard	60% – 74%	Moderate-to-vigorous transition (ventilatory threshold / aerobic conditioning target)
15 – 16	15 = Hard (heavy)	75% – 84%	Vigorous exercise intensity (approaching respiratory compensation point)
17 – 18	17 = Very hard	≥ 85%	High-intensity interval or near-maximal cardiopulmonary exercise testing (CPET)
19 – 20	19 = Extremely hard; 20 = Maximal exertion	100%	Volitional exhaustion / symptom-limited CPET termination endpoint

2. The Borg CR10 (0–10 Category-Ratio) Scale and Modified Borg Dyspnea Scale

While heart rate and oxygen uptake (VO₂) increase linearly with workload, specific physiological sensations—such as blood and muscle lactate accumulation, breathlessness (dyspnea), and localized muscular pain—follow a positively accelerating nonlinear power function (R = c · Sⁿ, where the exponent n ≈ 1.6 for ergometer cycling). To measure these sensations with true ratio properties, Borg developed the Borg CR10 Scale:

• Scale Architecture (0 to 10+): Runs from 0 (“Nothing at all”), 0.5 (“Extremely weak / just noticeable”), 1 (“Very weak”), 2 (“Weak / light”), 3 (“Moderate”), 4 (“Somewhat strong”), 5 (“Strong / heavy”), 7 (“Very strong”), 10 (“Extremely strong / almost maximal”), to an unnumbered open-ended maximum (• or *, “Absolute maximum”) to prevent ceiling effects.
• Modified Borg Dyspnea Scale in the 6-Minute Walk Test (6MWT): Adapted from the CR10 scale, the 0–10 Modified Borg Dyspnea Scale is mandated by American Thoracic Society (ATS) guidelines to record baseline and post-walk dyspnea and fatigue during the 6-Minute Walk Test alongside COPD and interstitial lung disease quality-of-life instruments such as the St George’s Respiratory Questionnaire (SGRQ).

What Standards and Clinical Guidelines Govern Borg RPE Administration?

In cardiopulmonary exercise testing (CPET), Phase II/III cardiac rehabilitation, and FDA clinical trials evaluating exercise tolerance endpoints, standardized administration of the Borg RPE is governed by American Heart Association (AHA), American College of Sports Medicine (ACSM), American Association of Cardiovascular and Pulmonary Rehabilitation (AACVPR), and American Thoracic Society (ATS) protocols:

• Exercise Prescription Under Beta-Adrenergic Blockade: Patients with coronary artery disease, heart failure, or arrhythmias frequently take beta-blockers, which blunt sinoatrial node chronotropic response and lower peak heart rate. In these patients—as well as patients with rate-responsive pacemakers, atrial fibrillation, or autonomic neuropathy after cardiac transplantation—heart rate formulas overestimate tolerable workload. AACVPR and AHA guidelines specify a target Borg 6–20 RPE range of 11 to 14 (“Light” to “Somewhat hard”) to titrate aerobic training intensity safely.
• Standardized Patient Instructions and Anchoring: Valid psychophysical measurement requires reading standardized pre-test instructions before exercise begins, instructing the participant to rate their overall feeling of exertion (or specifically differentiated central cardiorespiratory dyspnea versus peripheral leg fatigue) using the verbal anchors first and then selecting the corresponding number, while avoiding observer coaching or facial cues.
• CPET Submaximal vs. Peak Effort Verification: During symptom-limited cardiopulmonary exercise testing, a peak Borg 6–20 RPE of ≥ 17–18 (or Borg CR10 ≥ 7–8) alongside a Respiratory Exchange Ratio (RER = VCO₂ / VO₂ ≥ 1.10) serves as a primary criterion confirming that the patient achieved a true physiological maximal effort.

How Does the Borg Rating of Perceived Exertion Integrate With EHR and Health Informatics Workflows?

In electronic health records, remote cardiopulmonary telerehabilitation platforms, and clinical trial Electronic Data Capture (EDC) systems, Borg RPE scores are structured as discrete clinical observations paired with physiological telemetry:

• LOINC and SNOMED CT Terminology Bindings: The Borg 6–20 RPE scale is encoded in LOINC under code 89243-0 / 60842-2 (Perceived exertion during exercise [Borg RPE]) and SNOMED CT observable entity 251891004 (Borg rating of perceived exertion), while pre- and post-6MWT Borg CR10 dyspnea and fatigue scores are captured as discrete numeric observations linked to the exercise encounter.
• HL7 FHIR R4 Observation Pairing in Telerehabilitation: In home-based cardiac telerehabilitation, patients wear Bluetooth pulse oximeters or ECG patches streaming heart rate and SpO₂ while submitting in-app Borg RPE prompts at peak exercise and cool-down. The platform packages both streams as HL7 FHIR Observation resources, triggering clinical decision support alerts if a patient reports a sudden upward drift in RPE (e.g., RPE ≥ 15 at a previously light workload of 2–3 METs), which may signal decompensated heart failure, ischemia, or arrhythmia prior to overt vital sign collapse.