Borg Rating of Perceived Exertion Scale

1. Abstract

The Borg Rating of Perceived Exertion Scale (most notably the Borg 6–20 RPE Scale) is an internationally recognized psychophysical instrument developed by Swedish psychologist Gunnar Borg in the early 1970s. Designed to quantify an individual’s subjective experience of physical effort, fatigue, and physiological strain during muscular work, the scale operationalizes the theoretical intersection between subjective perception and objective exercise intensity. The classic instrument consists of a single-item, 15-point categorical ratio-interval continuum ranging from 6 (“No exertion at all”) to 20 (“Maximal exertion”), calibrated to approximate human heart rate values divided by ten (i.e., 60 to 200 beats per minute) in healthy young adults performing progressive cycle ergometry. This article examines the psychometric and psychophysical underpinnings of the scale, evaluating its criterion-related, construct, and convergent validity against systemic physiological indicators, including heart rate, blood lactate accumulation, oxygen consumption (VO2), and pulmonary ventilation. Furthermore, test-retest reliability coefficients consistently range between 0.70 and 0.95 across athletic, healthy sedentary, and diverse clinical cohorts, including individuals undergoing cardiac rehabilitation, pulmonary therapy, and specialized neurological interventions (e.g., Parkinson’s disease). We review the underlying neurophysiological and Gestalt sensory integration models that justify its clinical deployment, delineate factor-analytic models demonstrating its unidimensional structure of physical strain, detail administration protocols and standardized verbal instructions, and discuss linguistic adaptations, such as the Dutch Royal Dutch Society for Physical Therapy (KNGF) cardiac rehabilitation version.

2. Keywords

Borg RPE Scale, Perceived Exertion, Psychophysics, Exercise Physiology, Cardiac Rehabilitation, Subjective Workload, Ergometry, Fatigue Assessment, Physical Effort, Gunnar Borg

3. Authors

The foundational Borg Rating of Perceived Exertion Scale was conceptualized, mathematically calibrated, and validated by Gunnar A. V. Borg, Ph.D. (1927–2020), Professor of Psychophysics and Work Science at Stockholm University, Sweden. Over several decades of empirical inquiry, Professor Borg collaborated with distinguished exercise physiologists and cardiologists, including Per-Olof Åstrand, Hans Dahlström, and Gunnar Blom. Linguistic translations, population-specific normalizations, and clinical guidelines have been advanced by various international bodies; notably, the Dutch cross-cultural adaptation and clinical protocol integration were formalized by the Royal Dutch Society for Physical Therapy (Koninklijk Nederlands Genootschap voor Fysiotherapie; KNGF) within their 2011 Clinical Practice Guideline for Cardiac Rehabilitation (KNGF-richtlijn Hartrevalidatie).

4. Purpose

The fundamental purpose of the Borg Rating of Perceived Exertion Scale is to provide an accurate, non-invasive, cost-effective, and rapidly administered subjective metric that reflects the totality of internal physiological and psychophysiological stress experienced by an individual during exercise or occupational task performance. While objective physiological monitoring—such as continuous twelve-lead electrocardiography (ECG), automated blood pressure tracking, direct spirometric gas analysis, and serial blood lactate assay—provides precise measurements of isolated biological parameters, these modalities require specialized instrumentation, significant expertise, and can disrupt natural movement dynamics. More importantly, isolated physiological variables often fail to capture the holistic cognitive integration of central (e.g., cardiorespiratory, dyspneic) and peripheral (e.g., local muscle acidosis, mechanical joint strain, thermal discomfort) sensations that ultimately dictate an individual’s voluntary tolerance for physical effort.

From a clinical perspective, the Borg RPE scale addresses a critical safety and diagnostic gap, particularly in cardiac rehabilitation, pulmonary medicine, oncology, and geriatrics. For patients receiving negative chronotropic medications—such as beta-adrenergic antagonists (beta-blockers)—the natural chronotropic response of the heart to progressive metabolic demand is blunted or uncoupled. In such cohorts, traditional heart rate target zones derived from age-predicted maximal heart rate equations (e.g., 220 minus age) become entirely invalid and clinically hazardous. The Borg RPE scale serves as a primary surrogate marker of absolute and relative metabolic intensity, empowering patients to self-regulate work rate safely within prescribed perceptual target zones (typically between 11 [“Light”] and 14 [“Somewhat hard”]).

In neurological rehabilitation, particularly among patients diagnosed with Parkinson’s disease, the scale evaluates abnormal motor fatigue, autonomic dysregulation, and central effort-reward processing deficits. Parkinson-specific adaptations and instructional guidelines help physical therapists differentiate between muscular exhaustion, bradykinetic movement fatigue, and psychological apathy during ambulation and resistance protocols.

In athletic training, high-performance sports science, and occupational biomechanics, the scale serves dual functions: monitoring acute training intensity during graded exercise tests (GXT) or high-intensity interval sessions, and quantifying session-RPE (sRPE) to track cumulative internal training load over microcycles and mesocycles. By multiplying the session duration in minutes by the post-exercise RPE score, sport scientists monitor training strain, anticipate overtraining syndrome, and mitigate musculoskeletal injury risks.

5. Psychological Construct

The construct measured by the Borg RPE scale is Perceived Exertion, formally defined in psychobiology as the subjective feeling of strain, heavy breathing, muscular fatigue, and total physical effort experienced during physical work. This construct represents an integrated Gestalt perception rather than an isolated sensory modality. Perceived exertion operates at the nexus of psychological consciousness and biological homeostasis, dynamically constructed from two distinct yet inter-communicating physiological signal streams:

• Central Signals: These visceral afferent sensations originate primarily from the cardiopulmonary system. They encompass sensations of pulmonary ventilation, chest wall displacement, arterial oxygen desaturation, respiratory frequency, and the sensation of dyspnea or “air hunger.” Central signals are processed through brainstem respiratory centers, the thalamus, and the insular cortex, communicating how intensely the heart and lungs are working to meet systemic metabolic demands.
• Peripheral Signals: These somatic afferent sensations arise from the working skeletal musculature, tendons, and joints. They are driven by metabolic alterations within the active motor units, including intracellular hydrogen ion accumulation (acidosis), depletion of muscle glycogen, interstitial potassium efflux, temperature elevation, and mechanical tension transmitted through Golgi tendon organs and muscle spindles via Group III and IV mechanosensitive and metabosensitive sensory nerve fibers.

In addition to physiological inputs, the psychological construct of perceived exertion is modulated by cognitive, affective, and dispositional factors. Executive appraisal, somatic focus (associative versus dissociative attentional strategies), baseline distress tolerance, state and trait anxiety, self-efficacy, and motivational orientation alter the cognitive gain applied to afferent sensory signals. For instance, an athlete utilizing external associative strategies or experiencing high competitive motivation may down-regulate the conscious salience of lactic acidosis, assigning a lower numerical RPE value to a workload that would evoke a higher rating from a sedentary individual facing the same relative percentage of maximal oxygen uptake.

The construct is deliberately distinct from localized pain, psychological distress, or generalized task boredom. Although acute muscular pain (such as ischemic burn during isometric muscle contractions) and exertional breathlessness frequently correlate with high RPE ratings, perceived exertion represents the conscious synthesis of how heavy, strenuous, and demanding the task feels in its entirety. The individual integrates all internal cues into a singular ordinal-to-interval judgment reflecting their proximity to physical task failure.

6. Theoretical Framework

The theoretical framework underpinning the Borg RPE Scale is rooted in Psychophysics—the scientific discipline established by Ernst Heinrich Weber and Gustav Fechner that investigates the quantitative relationships between physical stimuli and the psychological sensations they produce. For decades, traditional sensory psychophysics focused on exteroceptive modalities, such as visual luminance, acoustic amplitude, and cutaneous pressure, leading to Fechner’s logarithmic law and later Stevens’s Power Law ($R = k \cdot S^n$, where psychological response $R$ is a power function of physical stimulus intensity $S$, scaled by an exponent $n$ and a constant $k$).

Gunnar Borg expanded classical psychophysical paradigms to interoceptive, somatic, and physiological domains. Borg observed that during dynamic muscular work performed on a cycle ergometer or treadmill, human metabolic expenditure increases linearly or curvilinearly relative to external resistance. However, the body’s physiological indicators behave differently: oxygen uptake and heart rate increase essentially linearly with progressive work rate, whereas blood lactate, pulmonary ventilation, and catecholamine release exhibit an upward exponential inflection point as work transitions past the ventilatory and anaerobic thresholds.

To capture both linear cardiopulmonary parameters and non-linear metabolic stressors within a single coherent operational framework, Borg formulated the Principle of Somatosensory Feedback Integration. According to this model, the brain acts as an advanced biocomputational processor that continuously samples afferent peripheral inputs (Group III/IV muscle afferents), central visceral inputs (vagal and glossopharyngeal baroreceptors and chemoreceptors), and efferent motor commands (corollary discharges or central motor copies). As the primary motor cortex discharges action potentials downward through the corticospinal tract to activate alpha motor neurons, an identical neural replica (“efference copy”) is routed directly to the sensory somatosensory cortex and the anterior insula. This efference copy provides an instantaneous, feed-forward estimation of motor command magnitude, which is then fine-tuned by afferent biological feedback from the periphery.

Borg constructed the 15-point scale (ranging from 6 to 20) using a linear perceptual continuum designed to correlate directly with normal human heart rate responses during progressive, submaximal-to-maximal aerobic exercise. Borg deliberately anchored the minimum value at 6 and the maximum at 20 so that multiplying the patient’s reported score by 10 would yield a close numerical approximation of their true concurrent heart rate:

$$\text{Estimated Heart Rate (b\pm)} \approx \text{RPE Score} \times 10$$

Thus, a score of 6 corresponds to a baseline resting heart rate of approximately 60 beats per minute, a rating of 13 (“Somewhat hard”) approximates 130 beats per minute (often aligning with the aerobic-anaerobic threshold boundary), and a rating of 20 represents an exhaustive heart rate of 200 beats per minute in a healthy young adult. By placing verbal anchors at systematically determined intervals calibrated using category-scaling psychophysics, Borg ensured that changes along the scale correspond to proportional changes in physiological strain.

7. Validity

The psychometric validity of the Borg RPE Scale has been documented across hundreds of experimental and clinical trials, establishing robust evidence for construct, criterion, convergent, and discriminant validity.

Criterion-Related and Concurrent Validity

Concurrent criterion-related validity is traditionally evaluated by correlating concurrent RPE scores with objective biological indicators of exercise intensity during standardized progressive graded exercise testing. Meta-analytic reviews (e.g., Chen et al., 2002; Noble & Robertson, 1996) report high-magnitude product-moment correlation coefficients between RPE and primary physiological markers:

• Heart Rate: Pearson $r$ values between RPE and heart rate consistently fall between $r = 0.80$ and $r = 0.93$ in healthy adults performing incremental cycle or treadmill exercise. In populations taking beta-adrenergic antagonists, the correlation remains moderate to strong ($r = 0.65$ to $0.82$), although the direct “$ imes 10$” heart rate scaling heuristic is uncoupled.
• Blood Lactate Concentration: The correlation between RPE and blood lactate accumulation ranges from $r = 0.75$ to $r = 0.92$. Notably, the blood lactate threshold (typically corresponding to an absolute value of 2.0 to 4.0 mmol/L) reliably emerges at an RPE anchor of approximately 13 to 14 (“Somewhat hard”), while the onset of blood lactate accumulation (OBLA) typically corresponds to an RPE of 15 to 16 (“Hard / Heavy”).
• Oxygen Consumption (VO2 and %VO2max): Strong linear relationships are routinely observed between RPE and percentage of maximal oxygen consumption, with correlations typically between $r = 0.85$ and $r = 0.95$. An RPE of 11–12 approximates 50–60% of VO2max, 13–14 corresponds to 65–75% of VO2max, and 17–18 reflects 85–95% of VO2max.
• Pulmonary Ventilation (VE): Because hyperventilation occurs past the respiratory compensation point, ventilation exhibits an exponential increase at higher work rates, mirroring the sharp upward perceptual inflection seen between RPE ratings of 16 and 20 ($r = 0.78$ to $0.89$).

Construct and Convergent Validity

Construct validity has been established by demonstrating that experimentally induced alterations in physiological capacity result in predictable shifts in Borg RPE ratings at identical absolute work rates. For example, when subjects perform exercise under conditions of acute hypoxia, glycogen depletion, environmental heat stress, or dehydration, RPE ratings rise systematically faster than under normoxic, glycogen-replete, or thermoneutral conditions at the exact same wattage or running velocity. Conversely, following weeks of structured aerobic exercise conditioning, an individual’s RPE at an absolute workload (e.g., cycling at 150 Watts) shows a statistically significant decrease, reflecting enhanced cardiovascular efficiency, increased stroke volume, and improved cellular oxidative capacity.

Discriminant Validity

Discriminant validity is supported by studies confirming that RPE measures a physical strain construct distinct from generalized psychological distress, state depression, or localized cutaneous discomfort. When distinct scales assessing affective valence (such as Hardy and Rejeski’s Feeling Scale) or specific musculoskeletal pain scales are co-administered during exercise, perceived exertion tracks metabolic workload continuously, even when emotional valence fluctuates independently due to cognitive reframing or verbal encouragement.

8. Reliability

The Borg RPE Scale demonstrates exceptional reliability across experimental paradigms, administration intervals, and patient populations. Because the instrument is a single-item metric, traditional internal consistency indicators (such as Cronbach’s alpha or split-half coefficients) cannot be mathematically computed for the scale in isolation. Instead, reliability is evaluated using test-retest reliability, intra-class correlation coefficients (ICC), and reproducibility across production versus estimation protocols.

Test-Retest Reliability and Intraclass Correlations

Across progressive exercise trials conducted under identical physiological, nutritional, and environmental conditions separated by 24 to 72 hours, test-retest reliability coefficients for the Borg 6–20 scale consistently range from $r = 0.75$ to $r = 0.94$. In clinical cohorts—including patients with coronary artery disease, chronic heart failure, and chronic obstructive pulmonary disease (COPD)—intra-class correlation coefficients (ICC) for treadmill walking at specified speeds typically exceed 0.85 (ranging from 0.82 to 0.91), demonstrating stable within-subject reproducibility.

Estimation versus Production Modes

Reliability has been confirmed using two classic psychophysical modes:

• Estimation Mode: The experimenter or clinician sets the physical workload (e.g., speed, grade, or cycling resistance), and the subject assigns an RPE rating at designated time intervals. Within-subject coefficients of variation in estimation mode typically average under 8% across repeated visits.
• Production Mode: The clinician specifies a target RPE (e.g., “maintain your effort at 13 on the scale”), and the subject adjusts ergometer resistance or running speed to match that target intensity. Research demonstrates high repeatability in production mode (ICC > 0.80), demonstrating that individuals can reliably self-regulate absolute exercise intensity based solely on their internal calibration of the Borg scale verbal anchors.

Standardization of participant instructions is critical for achieving high test-retest reliability. Studies indicate that when ambiguous, non-standardized instructions are given, measurement error increases significantly, leading to higher intra-individual rating variance ($p < 0.01$). When standardized written instructions and anchoring demonstrations (e.g., explicitly defining rating 6 as sitting quietly in a chair and rating 20 as maximal, all-out effort) are applied, random error is minimized.

9. Factor Analysis

Because the primary Borg RPE Scale is a single-item ordinal continuum, traditional Exploratory Factor Analysis (EFA) or Confirmatory Factor Analysis (CFA) applied directly to its isolated score is not structurally applicable. However, extensive psychometric investigations have applied factor analysis to multi-variable physiological matrices and multi-dimensional subjective effort inventories where the Borg RPE item was embedded alongside central, peripheral, affective, and biomechanical parameters.

Principal Component and Exploratory Factor Analysis

In classical factor-analytic studies of perceived exertion (e.g., Robertson, 1982; Noble & Robertson, 1996), factor analysis was conducted on matrices comprising RPE ratings, respiratory rate, minute ventilation, heart rate, cardiac output, respiratory exchange ratio, blood lactate, and electromyographic (EMG) root-mean-square amplitude across varying exercise protocols. These analyses typically yield a clean two-factor solution or an overarching unidimensional dominant factor:

• Factor 1: Metabolic / Cardiorespiratory Strain (Central Factor): The Borg RPE scale consistently loads heavily on this primary factor, displaying factor loadings between 0.78 and 0.91. Co-loading variables on this factor include percentage of VO2max, pulmonary ventilation ($V_E$), and heart rate. This confirms that the primary variance captured by the Borg scale represents systemic cardiorespiratory strain.
• Factor 2: Peripheral / Muscular Stress (Local Factor): During high-resistance protocols or exercise involving localized muscle groups (such as isolated knee extension or arm crank ergometry), RPE loads significantly onto a secondary peripheral factor (loadings between 0.65 and 0.84), sharing communality with blood lactate accumulation, localized muscle pain ratings, and surface EMG amplitude.

Structural Equation Modeling (SEM) and CFA

In more recent structural equation models investigating the cognitive architecture of exertion, perceived exertion is modeled as a higher-order latent variable informed by two first-order latent constructs: Cardiopulmonary Strain and Peripheral Musculoskeletal Strain. CFA fit indices from exercise physiology studies demonstrate excellent fit for this hierarchical structure:

• Comparative Fit Index (CFI) > 0.95
• Tucker-Lewis Index (TLI) > 0.93
• Root Mean Square Error of Approximation (RMSEA) < 0.06 (typically 0.042–0.058)
• Standardized Root Mean Square Residual (SRMR) < 0.05

These structural models verify that while the Borg RPE scale operates as a single operational item, it successfully captures a dual-source physiological phenomenon, weighting central and peripheral sensory inputs into a coherent, unidimensional output score.

10. Instrument / Measurement Tool

The Borg Rating of Perceived Exertion Scale is structured as follows:

• Instrument Type: Single-item psychophysical category-ratio rating scale.
• Administration Format: Visual chart presented on paper, large wall-mounted poster, or digital display, administered via verbal query, patient pointing, or computer touch interface.
• Item Count: 1 single item evaluating current global perceived physical exertion.
• Response Scale Continuum: 15-point numerical scale ranging from 6 to 20, containing 9 designated verbal anchors placed at odd and key even numbers:
• 6: No exertion at all
• 7: Extremely light
• 8: [Unanchored transitional step]
• 9: Very light
• 10: [Unanchored transitional step]
• 11: Light
• 12: [Unanchored transitional step]
• 13: Somewhat hard
• 14: [Unanchored transitional step]
• 15: Hard (heavy)
• 16: [Unanchored transitional step]
• 17: Very hard
• 18: [Unanchored transitional step]
• 19: Extremely hard
• 20: Maximal exertion
• Administration Protocol:
• The scale is placed directly in the patient’s field of vision throughout the exercise protocol.
• Before testing begins, the administrator delivers standardized verbal instructions: “During the exercise test, we want you to rate your total feeling of exertion. Look at the scale and read the words and numbers. Six means no exertion at all, like sitting quietly in a chair. Twenty means maximal exertion—the absolute hardest effort you could possibly make. Try to appraise your total feeling of effort, combining all sensations of physical stress, effort, and fatigue from your breathing, chest, and muscles. Do not focus on just one sensation; try to focus on your total inner feeling of exertion. Select the number that best describes your current effort.”
• During progressive testing, ratings are obtained during the final 15 to 30 seconds of each stage or workload increment.
• In clinical cardiac rehabilitation settings (e.g., KNGF guidelines), target training intensities are set between 12 and 14 for moderate endurance training, and between 14 and 16 for vigorous cardiovascular adaptation.
• Scoring and Interpretation:
• The reported number is recorded directly as the RPE score.
• Under 10: Very light activity; typical of warm-up or recovery pacing.
• 11 to 13: Light to moderate intensity; target zone for initial aerobic reconditioning in deconditioned cardiac and pulmonary patients.
• 14 to 16: Heavy/hard intensity; aligns closely with the physiological anaerobic threshold; appropriate for athletic conditioning and supervised phase-three cardiac rehabilitation.
• 17 to 19: Very heavy to extremely hard; near maximal performance; elite interval training and diagnostic stress tests.
• 20: Maximal exhaustion; termination point of diagnostic exercise testing.

11. Permissions & Fee and Test Year

Initial Publication Year: 1970 (preliminary 6–20 formulations published in the Scandinavian Journal of Rehabilitation Medicine); formal validation and expanded psychophysical scaling published in 1973 (Work Environment Health) and 1982 (Medicine & Science in Sports & Exercise).

Copyright and Proprietary Status: The specific arrangements of numerical intervals, verbal anchors, and instructional formulations developed by Gunnar Borg are protected under international copyright law. The official scales and instructional manuals are held by Borg Perception AB (Hässelby, Sweden; official website: www.borgperception.se) and published through Human Kinetics (e.g., Borg’s Perceived Exertion and Pain Scales, 1998).

Permissions and Licensing:

• Academic, Clinical, and Non-Commercial Research: Brief extracts, observational use in direct clinical patient care, and educational discussions of the scale are widely accommodated in international clinical practice guidelines, such as the American College of Sports Medicine (ACSM) and the Royal Dutch Society for Physical Therapy (KNGF). However, researchers reproducing the full original scale charts in peer-reviewed publications, dissertations, or psychometric databases must obtain written permission from Borg Perception AB.
• Commercial Use, Medical Devices, and Digital Applications: Any commercial integration of the Borg 6–20 scale into clinical software, wearable devices, digital fitness platforms, or commercial monitoring apparatus requires a formal licensing agreement and fee payment arranged directly through Borg Perception AB.

12. References

Borg, G. A. (1970). Perceived exertion as a parameter with physiological and psychological bases. Scandinavian Journal of Rehabilitation Medicine, 2(2), 92–98. https://pubmed.ncbi.nlm.nih.gov/5523831/

Borg, G. A. (1973). Perceived exertion: A note on “history” and methods. Work Environment Health, 10(2), 67–70.

Borg, G. A. (1982). Psychophysical bases of perceived exertion. Medicine & Science in Sports & Exercise, 14(5), 377–381. https://doi.org/10.1249/00005768-198205000-00012

Borg, G. (1998). Borg’s Perceived Exertion and Pain Scales. Human Kinetics. ISBN: 9780880119641.

Chen, M. J., Fan, X., & Moe, S. T. (2002). Criterion-related validity of the Borg ratings of perceived exertion scale in healthy individuals: A meta-analysis. Journal of Sports Sciences, 20(11), 873–899. https://doi.org/10.1080/026404102320761787

Koninklijk Nederlands Genootschap voor Fysiotherapie (KNGF). (2011). KNGF-richtlijn Hartrevalidatie. Nederlands Tijdschrift voor Fysiotherapie, Supplement 2011. https://www.kngf.nl/

Noble, B. J., & Robertson, R. J. (1996). Perceived Exertion. Human Kinetics. ISBN: 9780873224727.

Robertson, R. J. (1982). Central signals of perceived exertion during dynamic exercise. Medicine & Science in Sports & Exercise, 14(5), 390–396. https://doi.org/10.1249/00005768-198205000-00014

Scherr, J., Wolfarth, B., Christle, J. W., Pressler, A., Wagenpfeil, S., & Halle, M. (2013). Associations between Borg’s rating of perceived exertion and physiological exercise parameters in healthy adults: The Posch study. European Journal of Applied Physiology, 113(1), 147–155. https://doi.org/10.1007/s00421-012-2421-x

13. Items of the Scale