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Journal of Physical Therapy Science logoLink to Journal of Physical Therapy Science
. 2026 Jul 1;38(7):324–329. doi: 10.1589/jpts.38.324

Design and development of a universal OMNI exertion faces scale

Amy Schlessman 1,*, Rick Wickstrom 2, Chris Petrosino 3, Robert Robertson 4
PMCID: PMC13318445  PMID: 42382020

Abstract

[Purpose] To design and develop a new OMNI Exertion Faces Scale (OMNI Faces) that uses universal design criteria to improve acceptability for measuring perceived exertion across age groups, physical activities, and clinical populations. [Methods] The OMNI Faces Scale was developed in collaboration with the original OMNI creator and refined through consultations with educators, speech-language pathologists, clinicians, and feedback from children and adults. Design considerations included universal accessibility, simplified instructions, and alignment with the Heart Rate Reserve method. [Design Features] The OMNI Faces Scale includes five verbal descriptors and five pictorial images to reduce inconsistencies with language, activity-specific visuals, and anchoring among prior versions. The OMNI Faces Scale is non-gendered, non-activity-specific, and has accessible fonts. Instructions were simplified to 71 words relevant for assessing perceived exertion during both aerobic and resistance activities. [Conclusions] The OMNI Faces Scale was designed to provide a versatile and inclusive tool for monitoring exertion in children and adults across a broad range of physical activity applications. Future research will validate its psychometric properties across populations and activity types and explore multilingual adaptations.

Key words: Perceived exertion, OMNI Faces Scale, Physical activity

INTRODUCTION

Perceived exertion has been defined as a person’s feelings of effort, strain, discomfort, and/or fatigue when engaged in exercise or other physical activities1). Gunnar Borg was the Swedish psychologist who introduced a simple category scale (Borg’s RPE Scale) for persons to provide a rating of perceived exertion (RPE) based on selecting a number from 6–20 with consideration of anchoring verbal descriptors2). The OMNI Picture System of Perceived Exertion (OMNI) is a collection of RPE category scales inspired by Robert Robertson that use numbers ranging from 0–10 with anchoring verbal descriptors and pictures of persons engaged in progressive physical work tasks. OMNI is not an acronym, but was chosen from the word omnibus, implying the scale can be broadly used1, 3). OMNI scales for RPE are practical tools for monitoring a person’s RPE response to physical work and exercise activities to reduce the risk of injury to children and adults.

Many variations of the OMNI have been studied with adults and children performing aerobic or resistance physical activity. The OMNI has also been studied in patients with a variety of diagnoses4,5,6,7,8,9,10,11,12,13,14,15,16). When using the OMNI, adults and children are asked to select a number from 0 to 10 that best corresponds with their perceived intensity of physical exertion17). Participants were instructed to consider corresponding pictorial images and verbal descriptors to select the numerical rating17). Verbal descriptors are placed on the scale at 0, 2, 4, 6, 8, and 10. Images specific to the type of activity performed were placed above the incline for the OMNI scale at approximately 0, 3, 6, and 917). Although on some versions of the OMNI, some physical activity images traverse more than one number on the scale (i.e. cycling, stepping)17). A sampling of physical tasks that have been validated on the OMNI scales at progressive intensities as shown in Fig. 117).

Fig. 1.

Fig. 1.

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Montage of picture cues for the OMNI perceived exertion scales.

Reprinted, by permission, from Robertson RJ. Perceived Exertion for Practitioners: Rating Effort with the OMNI Picture System, Champaign: Human Kinetics, 2004.

The numerous versions of the OMNI Exertion Scales that have been researched over the last 25 years that present images of specific physical activities contain inconsistencies that are limiting to applications and interpretation of ratings18). Within the OMNI Pictorial System of Perceived Exertion Scales, there are varying pictorial images and varying verbal descriptors between scales18). OMNI scale versions for adults use the keywords, easy and hard, whereas some OMNI scale versions for children use a different keyword in verbal descriptors for aerobic versus resistance physical activity. For resistance physical activity, OMNI scale versions for children use the keywords, easy and hard19), whereas for aerobic physical activity, a different keyword, tired, was used20). Some adult scales used the keyword, tired, commonly used for the children aerobic physical activity scales, instead of, easy and hard, including a scale for adult farmworkers21) and a scale for adults propelling a manual wheelchair22). Many OMNI scale versions present pictures and verbal descriptors anchored at the zero point that are not consistent with a resting posture. The OMNI bench stepping scale of perceived exertion by Kraus et al. was the first OMNI version to anchor the verbal descriptor “Rest” at the zero point; however, this scale depicted a standing rather than a seated rest posture23).

Each of the OMNI scale versions for adults include pictorial variations of an adult performing a specific type of physical activity such as resistance exercise with barbells, treadmill running, cycling, elliptical machine, elastic resistance exercise bands, bench stepping, manual wheelchair propulsion, farm workers harvesting apples, to name a few. Versions of the OMNI for children include pictorial variations of a child performing activities such as running, walking, cycling, resistance exercise with dumbbells, and stepping up stairs. The OMNI scales for adults and children also have male and female versions for the various activities17). Additionally, the instructions for the many versions of the OMNI scales vary between specific physical activities and between the adult and children scales, with all versions having lengthy instructions, at approximately 200 words.

A review of variations of the OMNI for adults for physical therapy practice called for uniformity amongst the adult scale versions18). A recent scoping review in 2021 questioned the OMNI’s inconsistencies in use of verbal descriptors between adult and children’s versions as well as the choice of the verbal descriptor tired for the children’s aerobic physical activity scale24). The review pointed out that feeling tired can be used to describe sleepiness versus effort, possibly resulting in an undesirable perception of physical activity, especially with the verbal descriptor not at all tired at “0” and a little tired at “2” on the 0–10 scale24).

Given these inconsistencies across OMNI scale versions, we hypothesized that a more universal OMNI Exertion Faces Scale would decrease inconsistencies and improve applicability across a broader range of participant ages, populations, and physical activities.

METHODS

This technical note presents the design rationale and development process for the OMNI Faces Scale. An initial OMNI scale modification was made in a pilot study25), in collaboration with the original OMNI developer, Robert Robertson, who is a co-author on this manuscript25). That pilot study produced a color version modification that depicted a vertical thermometer with the inclusion of “Resting” and a seated rest image to anchor the zero point25). That thermometer version of the OMNI was used in that pilot study comparing OMNI ratings with the Borg 6–20 Rating of Perceived Exertion using a stepping endurance task25). In that pilot study of a healthy sample, the generic version of the OMNI Exertion Scale was found to be highly correlated with the Borg (r=0.93)25). In that pilot study the OMNI prediction was highly correlated with actual HR, compared to only moderate correlation for the Borg prediction method multiplied RPE by 1025).

That pilot study25) prompted an iterative process to further develop a more universal version of the OMNI with faces to measure a broad variety of physical tasks or physical activities with adults and children. Variations in the progression of facial expressions were piloted for feedback by individuals and professionals. Decisions about the scale were made by consensus voting of the authors for this paper. Our main purpose was to simplify, make clearer, and standardize a more generalizable version of the OMNI that presented facial expressions rather than specific activities. This final version developed by Rick Wickstrom, Amy Schlessman, and Robert Roberston, with the graphic design assistance of Ella Schlessman, is titled the OMNI Exertion Faces Scale (OMNI Faces) (Fig. 2). OMNI Faces allows individuals, practitioners and researchers to use the same visual scale and same instructions, regardless of whether the activity is aerobic or resistance, creating more commonality for assessing perceived exertion in work, fitness, clinical or research applications.

Fig. 2.

Fig. 2.

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The New OMNI Exertion Faces Scale.

Formal psychometric validation is planned as a separate study. OMNI Faces was designed with the intent to align with the Heart Rate Reserve method of interpreting or prescribing the intensity of workload for a given physical activity by positioning “Resting” at the zero point of the scale23), future studies will be needed to validate whether this design intent translates to clinical practice. Heart Rate Reserve (HRR) represents the capacity for heart rate to increase in response to physical activity. It is the numerical range between baseline heart rate at rest and maximum heart rate at peak performance level. This alignment parallels the HRR calculation for determining the target heart rate for cardiorespiratory training: [HRR = (HRmax − HRrest) × %intensity + HRrest], where resting heart rate serves as the baseline (zero intensity), authors propose that this may allow practitioners to use consistent baseline anchoring across both physiological and perceptual measures. As a proposed practical heuristic, multiplying the OMNI Faces rating by 10 may provide a convenient way to estimate the approximate percentage of HRR when prescribing exercise intensity, pending formal validation of this relationship. It is anticipated that this alignment may support safer monitoring of physical activity in individuals on medications affecting heart rate, pending formal validation. Similarly, as another proposed practical heuristic, multiplying the OMNI Faces rating by 10 may provide a way to estimate the percentage of maximum capacity to guide strength training intensity without exposing individuals to unnecessary risks to assess maximum strength levels, pending formal validation of this relationship.

Previous OMNI Scales had six verbal descriptors with four non-corresponding pictorial images. OMNI Faces has 5 verbal descriptors with 5 corresponding pictorial images, to align with the Heart Rate Reserve method of interpreting or prescribing the intensity of workload for a given physical activity25). Figure 2 presents the OMNI Faces. This scale positions “Medium [Moderate]” at “5”, removing verbal descriptors “Somewhat easy”/“Getting more tired” from “4” and removing “Somewhat hard”/“Tired” from “6”. The terms, “Light”, “Moderate”, and “Heavy” are familiar descriptors used in occupational information systems to I the strength exertional levels for lifting and carrying tasks. The term, “Moderate” is a relevant level of exercise intensity that has been associated at 40 to 59% of the HRR. The terms “Light” and “Heavy” are also familiar descriptors that have been used to classify the exertional intensity of cardiorespiratory endurance activities. This justified our decision to anchor the verbal descriptor “Medium [Moderate]” over number 5, associate “[Light]” after “Easy” over number 2, and associate “Heavy” after “Hard” over number 8 on the OMNI Faces. On the OMNI Faces scale, the bracketed terms “[Light]” after “Easy”, “[Moderate]” after “Medium,” and “[Heavy]” after “Hard” are visually displayed simultaneously directly below the primary verbal descriptor on the scale and serve as supplementary labels to facilitate recognition across clinical and occupational contexts.

OMNI Faces was designed with clinical application in mind, for interpreting or prescribing intensity of workload for a more general range of physical activities or other lifestyle activities for adults and children.

OMNI Faces considers universal design principles, font, color accessibility, and simplified instructions from around 200 words to 71 words. The colors chosen met the Web Content Accessibility Guidelines (WCAG) to be accessible and compliant for individuals with visual impairments, including color contrast, small text and large text for both level AA and level AAA, as well as for graphics and user interface (UI)26). The color scheme was designed to meet WCAG Level AA standards (minimum contrast ratio 4.5:1) for all text elements and Level AAA standards (contrast ratio 7:1) for critical scale components, ensuring accessibility for individuals with visual impairments including color vision deficiencies26). Modifications to the instructions and verbal descriptors were refined through consultations with three elementary and middle school language arts teachers and two speech-language pathologists who reviewed draft versions and provided feedback on age-appropriateness and clarity. Input was received from children and adults known to the developers on the line thickness, color of faces, and facial expressions. Research on facial expressions during exertion was also utilized in facial expression development27).

DESIGN FEATURES

OMNI Faces was successfully developed through collaboration with the original OMNI Scale creator and refined by a multidisciplinary team. The final version includes five pictorial images paired with five verbal descriptors, designed to be universally applicable across age groups, activity types, and ability levels. Key design improvements include: alignment with the Heart Rate Reserve method by positioning “Resting” at zero; removal of ambiguous mid-range descriptors to enhance clarity; simplified instructions (reduced from ~200 to 71 words); accessibility-compliant color and font choices per WCAG standard; and input from educators, speech-language pathologists, and individuals across age groups to refine facial expressions and visual elements.

These modifications resulted in a scale that is visually simplified, linguistically simplified, and broadly applicable for both clinical and research settings.

DISCUSSION

Determining exercise intensity across diverse populations, for adults and children across a wide range of abilities, is essential for safe and effective exercise prescription, physical task analysis, and physical activity programming. RPE considerations are important to designing and progressing physical activity programs and physical task progression. The OMNI Faces Scale intends to address this need by offering a universal, low-risk, cost-free tool that requires no equipment or complex monitoring. Its design is intended to support use in a variety of settings including schools, clinics, workplaces, and community settings, for practitioners working with children, adults, older adults, or individuals with disabilities.

A limitation of this technical note is the preliminary nature of the multidisciplinary consultation process used to inform the current design of OMNI Faces, as this OMNI Faces design was a preliminary step for a future research study to further examine test-retest reliability, predictive validity and acceptability of the OMNI Faces compared to the Borg CR10 Scale in youth and adults. Another limitation of this technical note is the absence of formal psychometric validation data, where future research is needed on the reliability and validity for the OMNI Faces. Design differences between the many prior versions of the OMNI scale have limited the generalizability of previous versions that were activity-specific or designed for a specific age group, so future research will focus on validating the simplicity and clarity of OMNI Faces to support individualized monitoring of perceived exertion for progressive activity planning across strength, endurance, work, and everyday tasks. By incorporating principles of universal design and accessibility, OMNI Faces is intended to promote equitable participation in physical activities and safe activity progression for individuals of all abilities. Planned work also includes evaluation across diverse settings and populations, including workplace applications as a psychophysical outcome measure, and translation into multiple languages to enhance global applicability and inclusivity.

Future validation studies will examine the concurrent validity of OMNI Faces against established physiological criterion measures, including heart rate and oxygen consumption, as well as its convergent validity with the Borg CR10 scale. Test-retest reliability will be evaluated using the intraclass correlation coefficient, with a priori threshold of ICC ≥0.80 considered acceptable. Responsiveness will be assessed through calculation of the minimal detectable change (MDC) to support clinical decision-making.

Conflict of interest

Authors Rick Wickstrom (second author), Amy Schlessman (first author), and Robert Robertson (fourth author) developed the OMNI Exertion Faces Scale. Christopher Petrosino (third author) declares no conflict of interest. This universal design project to develop the OMNI Faces Exertion Scale was Dr. Robertson’s last research contribution as a Professor Emeritus at the University of Pittsburgh before he passed away peacefully on November 14, 2025, at age 82. His patience, clarity, and encouragement shaped countless careers of students and colleagues and reflected his lifelong passion for exercise science across the lifespan.

Acknowledgments

The authors would like to acknowledge the graphic design assistance of Ella Schlessman in creating the illustration for the OMNI Exertion Faces Scale. The authors would also like to acknowledge Robert Robertson, original developer of the OMNI and co-developer of OMNI Faces, for his lifetime of research dedicated to perceived exertion.

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