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00005768-200605000-0002800005768_2006_38_1014_roemmich_perceived_5article< 69_0_12_5 >Medicine & Science in Sports & Exercise©2006The American College of Sports MedicineVolume 38(5)May 2006pp 1014-1019Validity of PCERT and OMNI Walk/Run Ratings of Perceived Exertion[SPECIAL COMMUNICATIONS: Methodological Advances]ROEMMICH, JAMES N.1,2; BARKLEY, JACOB E.1; EPSTEIN, LEONARD H.1,3; LOBARINAS, CHRISTINA L.1; WHITE, TRESSA M.1; FOSTER, JAMEE H.11Department of Pediatrics, School of Medicine and Biomedical Sciences, University at Buffalo, Buffalo, NY; 2Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, NY; and 3Department of Social and Preventive Medicine, University at Buffalo, Buffalo, NYAddress for correspondence: James N. Roemmich, Ph.D., State University of New York at Buffalo, Department of Pediatrics, Farber Hall, Room G56, 3435 Main Street, Building #26, Buffalo, NY 14214-3000; E-mail: for publication March 2005.Accepted for publication October 2005.ABSTRACTPurpose: This study was conducted to test the validity of the Pictorial Children's Effort Rating Table (PCERT) and OMNI walk/run scales.Methods: Children (26 boys age 11.2 yr ± 1.6 and 25 girls age 11.1 yr ± 1.4) performed a five-stage incremental exertion treadmill test. The undifferentiated perceived exertion from the PCERT and OMNI scales was assessed for construct validity using Pearson correlations with V̇O2 and heart rate as criteria and concurrent validity by correlating PCERT and OMNI scores.Results: Increases in PCERT and OMNI scale scores were correlated with increases in V̇O2 (r = 0.90 and 0.92) and heart rate (r = 0.89 and 0.92). No difference was found in slope of the PCERT and OMNI scores when regressed against heart rate or V̇O2 and the slopes were invariant across sexes. To test concurrent validity of the PCERT and OMNI scales, subject scores at each stage were converted to a percentage of the maximal scale. No effect of sex was noted on perceived exertion (P = 0.32), and the percentage of the maximal PCERT and OMNI scales was almost identical at each stage (P = 0.73).Conclusions: Validity of both the PCERT and OMNI scales was established for submaximal exercise. PCERT and OMNI scores are not interchangeable because they have different scales, but at a given exercise intensity youth assign similar percentages of the maximal scores.Perceived exertion scales are commonly used to quantify effort sensations that are in part caused by metabolic changes during exercise (4). Initially perceived exertion scales developed for adults were also used to assess the perceptions of physical exertion in children and adolescents (4). Many children, however, do not yet have the cognitive ability or vocabulary to understand the descriptors of exercise intensity associated with adult perceived exertion scales (4,10,16). Children also have difficulty assigning words or phrases to numbers to describe their exertion (16) and may be better able to interpret illustrations that depict various stages of effort (4). Attention is now being paid to developing and validating perceived exertion scales specifically for youth.The Pictorial Children's Effort Rating Table (PCERT) (17) is a variation of the original nonpictorial CERT (5,16) and includes illustrations depicting levels of physical effort as well as descriptors of exercise intensity chosen by children. The PCERT descriptors of exercise intensity are identical to those used in the CERT and includes numbered exertion levels from 1 to 10, verbal cues ranging from "very, very easy" to "so hard I'm going to stop," and illustrations of a child walking up stairs and becoming more fatigued every two steps. The PCERT is linearly related to power output across a wide range of submaximal workloads, and children are able to utilize the PCERT to regulate their exercise intensity across four prescribed levels of perceived exertion (17). Thus, the PCERT may have utility for exercise prescription and exercise regulation (17).The OMNI walk/run scale of perceived exertion is a pictorial scale that has also been developed for use by children (15). The OMNI scale displays both pictorial descriptors and semantically consonant verbal descriptors distributed along a numerical category response range (10,15). The category format of the OMNI scale is distinct from the PCERT because the three components of the scale (verbal descriptors, pictorial descriptive, numerical categories) were developed in consort and validated as a single format (10,15). Specific versions of the OMNI scale have documented concurrent and construct validity for use with weight-bearing (7,15) and non-weight-bearing (9,11) aerobic exercise as well as resistance exercise (12). The OMNI walk/run scale includes exertion levels from 0 to 10, verbal cues ranging from "not tired at all" to "very, very tired," and illustrations of physical exertion with the child getting more fatigued as the child progresses to the top of the hill. Comparatively few validation data are available for the OMNI walking/running scale (7,15) or PCERT scale (17). Further validation by a variety of research groups is necessary to establish general validity of the PCERT and OMNI walk/run scales.This study was conducted to utilize a perceptual estimation paradigm to test the concurrent and construct validity of the PCERT and OMNI walk/run scales for children performing a submaximal progressive treadmill exercise test. We hypothesized that the PCERT and OMNI scales would demonstrate concurrent validity for assessing perceived exertion in children in that both would be linearly related to physiologic measures (heart rate, V̇O2) of exercise intensity. We also hypothesized that the PCERT and OMNI scales would demonstrate construct validity for assessing submaximal perceived exertion of children because both the scales are based on Borg's range model of category scaling (1,2), include illustrations of walk/run effort and verbal expressions chosen by children to describe effort levels, and use similar scales.METHODSSubjects.Study participants included 26 boys (N = 23 white, N = 3 African-American) and 25 girls (N = 22 white, N = 1 African-American, 1 Asian, and 1 other). Chi-square analysis revealed that racial distribution did not differ across the sexes (P = 0.39). Subjects were recruited from the local community through newspaper advertisements and targeted mailings. Clinical conditions, including cardiovascular, neuromotor, or cognitive disorders that would interfere with exercise testing or perceived exertion, were prescreened using a telephone interview with each subject's parent. Subjects were participants in a larger longitudinal investigation of increasing physical activity in youth. Data presented in this paper are from baseline testing. Before describing the PCERT and OMNI walk/run scales to participants, each child was asked whether he or she had ever seen the scales before. All children indicated that they had not seen either scale before the testing session. Written informed parental consent and subject assent were obtained for each subject before participation. This study was approved by the University at Buffalo School of Medicine institutional review board.Experimental design.A perceptual estimation paradigm was utilized to test the concurrent validity of the PCERT and OMNI walk/run scales. This was accomplished during a load-incremented treadmill test designed to determine the physical working capacity at a heart rate of 170 beats·min−1 (PWC 170). Subjects became familiar with the treadmill by walking on a level grade at 56.4 m·min−1 for 2 min, 69.6 m·min−1 for 2 min, and 85.8 m·min−1 for 3 min. Subjects then rested for 10 min. The perceptual estimation paradigm then consisted of walking at a level grade at 56.4 m·min−1 for 3 min, 69.6 m·min−1 for 3 min, and 85.8 m·min−1 for 3 min. The speed and grade were then increased to 99.2 m·min−1 and 2.5% grade for 3 min, then to 99.2 m·min−1 and 5.0% grade for an additional 3 min. During the final 20 s of each stage, subjects reported their undifferentiated (total body) perceived exertion using both the PCERT and OMNI walk/run scales. The speeds and grades for the perceptual estimation paradigm were selected based on previous research that the workloads would elicit a heart rate of approximately 55, 65, 75, and 85% of heart rate peak. The presentation order of the scales was counterbalanced across subjects and allowed for testing of construct validity of the two scales. Heart rate and V̇O2 were measured throughout the test. Heart rate was recorded during the final 20 s of each stage, and V̇O2 was averaged across the last minute of each stage.Anthropometry.Height was assessed using a calibrated stadiometer (Seca, Hamburg, Germany) to the nearest 1.0 mm. Weight was measured to the nearest 0.05 kg with the subjects wearing shorts and a T-shirt using a balance beam scale (Detecto, Webb City, MO) calibrated daily. Skinfold sites included the subscapular, triceps, suprailiac, abdominal, and medial calf. Skinfolds were measured with a calibrated Lange calipers (Beta Technology Inc, Santa Cruz, CA). Each skinfold was measured three times and the median score was used as data to avoid the effects that an outlying measure may have on the mean score. All of the anthropometric measures were performed by an experienced anthropometrist. Adiposity was assessed by summing the five skinfold thicknesses, and body composition was estimated from triceps and calf skinfold thicknesses using equations validated against a four-compartment model of body composition in youth of the same age as those in this study (14).Aerobic fitness.The rate of oxygen consumption and ventilation was measured throughout the treadmill test using a Vmax metabolic cart (Sensormedics, Yorba Linda, CA). The Vmax system was calibrated before each test with two separate gas mixtures supplied by Sensormedics, one containing 16% O2 with 4% CO2, and a reference mixture containing 21% O2 with balanced N2. Heart rate was recorded using a Polar HR Monitor (Polar Electro, Inc., Woodbury, NY). V̇O2peak was estimated based on linear regression of the heart rate and V̇O2 measurements and an estimated maximal heart rate of 200 beats·min−1. Research has shown that maximal heart rate is stable at 200 beats·min−1 (± 9 beats·min−1) throughout childhood and adolescence (3,13).Ratings of perceived exertion.Immediately before the treadmill test, subjects were shown the PCERT and OMNI walk/run scales one at a time and their use was explained following specific instructions. An undifferentiated perceived exertion was defined for both scales as "How tired does your body feel during exercise?" (15). A standardized set of written instructions for the use the scales was read to each child. The instructions were taken from the original OMNI walk/run scale validation paper (15) and read verbatim when explaining the use of the OMNI walk/run scale. The instructions were modified when explaining the use of the PCERT in that the verbal descriptors and scale numbers in the script were changed to correspond with the low (1: very, very easy) and high (10: so hard I'm going to stop) anchors of the PCERT scale. Low and high perceptual anchors for both scales were established by having children think about a perceived exercise intensity that agreed, in their mind, with the pictorial descriptor of the boy walking at the bottom of the hill (CERT walk/run) or stairs (PCERT) and top of the hill (CERT walk/run) or stairs (PCERT). Cognitive anchor use is described for both scales (15,17). For both scales, children pointed to a number representing their rating of perceived exertion (RPE) because the mouthpiece used to collect metabolic measures limited their ability to provide a verbal rating of RPE. Children were assured that there were no "right or wrong" answers.Data analysis.Differences in physical characteristics, predicted V̇O2peak, and PWC 170 between boys and girls were analyzed with separate one-factor analyses of variance (ANOVA). Perceived exertion and physiologic responses to treadmill testing were tested with separate two-factor ANOVA, with sex as a between-subjects factor and treadmill test stage as a within-subjects factor. Changes in perceived exertion and physiologic responses between successive treadmill stages were tested for statistical significance with planned post hoc contrast statements. PCERT scale scores range from 1 to 10, and OMNI walk/run scales scores range from 0 to 10. To directly compare PCERT and OMNI walk/run data, subject scores at each stage were converted to a percentage of the maximal score for the perceived exertion scale. Three-way ANOVA was used to determine differences in percentage maximal perceived exertion across treadmill test stages with sex as a between-subjects factor and perceived exertion scale and treadmill test stage as within-subjects variables. Slopes and correlation coefficients (r) were calculated for each subject by regressing their five PCERT and five OMNI walk/run scores against their five heart rate and five V̇O2 scores. Differences in slopes and intercepts were tested with two-way ANOVA with sex as a between-subjects factor and perceived exertion scale as a within-subjects factor. Concurrent validity of the PCERT and OMNI walk/run scales was determined by averaging the correlation coefficients of all subjects for each scale. Differences in correlation coefficients between the two perceived exertion scales and between boys and girls were compared using a two-tailed Fisher z-transformation. Construct validity was assessed by correlating the percentage of the maximal scale scores of the PCERT and OMNI walk/run scales across the five treadmill stages for each child and then averaging the correlation coefficients of all subjects.RESULTSPhysical characteristics for boys and girls are shown in Table 1. No differences were seen in age (P = 0.79), height (P = 0.91), weight (P = 0.73), sum of skinfold thickness (P = 0.98), and percentage body fat (P = 0.43) of the boys and girls. Boys had a greater PWC 170 (P ≤ 0.03) and predicted V̇O2peak (P ≤ 0.03) than the girls. No sex differences were found in perceived exertion or physiologic responses during the treadmill testing (Table 2), but all perceived exertion and physiologic responses increased (P ≤ 0.001) progressively from one test stage to the next. The linear relationships between mean PCERT or mean OMNI walk/run scores and mean V̇O2 or mean heart rate are shown in Figure 1. As shown in Table 3, the mean slope of increase in PCERT and OMNI walk/run scores was invariant across the sexes and across perceived exertion scales when regressed against either heart rate or V̇O2. Significant sex by perceived exertion scale interaction effects were noted for the intercepts (P ≤ 0.03). For both the heart rate and V̇O2 regressions, the intercepts of the PCERT scale were lower than the intercepts of the OMNI walk/run scale in girls, but no difference was found in intercepts of the boys. Correlations between increases in the perceived exertion and physiologic measures of exercise intensity, also shown in Table 3, ranged from 0.86 to 0.94. No differences were found in magnitude of the correlation coefficients between the two perceived exertion scales or between boys and girls. As shown in Figure 2, boys and girls assigned a similar percentage of the maximal PCERT and OMNI walk/run scales at each workload (P = 0.32). The percentage of the total PCERT and OMNI walk/run scales was almost identical at each workload (P = 0.73). The construct validity analysis of the correlation between the percentages of the maximal PCERT and OMNI walk/run scores produced a coefficient of 0.92.FIGURE 1-Response linearity of perceived exertion of the OMNI walk/run and Pictorial Children's Effort Rating Table (PCERT) when plotted against the rate of oxygen consumption (upper panel) and heart rate (lower panel) of boys and girls.FIGURE 2-Response linearity of percentage maximal possible perceived exertion of the OMNI walk/run and Pictorial Children's Effort Rating Table (PCERT) when plotted against percentage maximal oxygen consumption (upper panel) and percentage maximal heart rate (lower panel) of boys and girls. The PCERT and OMNI walk/run scales have different numeric ranges. To directly compare PCERT and OMNI walk/run data, subject scores at each stage were converted to a percentage of the maximal score for the perceived exertion scale.TABLE 1. Physical characteristics of the subjects.TABLE 2. Ratings of perceived exertion variables of the boys and girls.TABLE 3. Slopes, intercepts, and correlation coefficients for increase in perceived exertion scores with increases in heart rate and oxygen consumption during treadmill exercise.DISCUSSIONA perceptual estimation paradigm was used to test the concurrent validity of the PCERT and OMNI walk/run perceived exertion scales during submaximal treadmill exercise. The OMNI walk/run scale has not been widely tested for concurrent validity (7,15). Likewise, only one report of the validity of the PCERT has been published (17).In the present experiment, significant increases were noted in both physiologic responses and effort perception between each treadmill stage. Both the PCERT and OMNI walk/run scales provided valid estimates of submaximal effort perception as demonstrated by robust correlations (Table 3) and linear regressions with physiologic measures of effort, including heart rate and V̇O2 (Figs. 1 and 2). Linearity of responses with physiologic measures was invariant across sexes, and the perceived exertion scales had almost identical concurrent validity. The magnitude of the correlations with heart rate (Table 3) is similar to previous work for the PCERT scale (17) and CERT scale (6). This is the first attempt to validate the PCERT scale against V̇O2, and it is encouraging that it correlates equally high with heart rate and V̇O2. Correlations of the OMNI walk/run scale with heart rate and V̇O2 were greater than the previously reported correlations of r = 0.23-0.47 (15). Previous studies of the PCERT scale (17) and of various forms of the OMNI scale (8,10-12,15) have also demonstrated linear responses with heart rate, V̇O2, or both. Thus, this experiment has shown that in the hands of an independent group of investigators, youth 8-12 yr of age can reliably interpret the words and pictures on both the PCERT and OMNI walk/run scales to provide equally valid numeric ratings of perceived exertion at submaximal exercise intensities. The treadmill protocol elicited heart rate and V̇O2 responses of approximately 84 and 75% of predicted maximum, so we could not assess response linearity beyond these values.In agreement with our hypothesis, a high positive correlation (r = 0.92) was found between scores from the PCERT and OMNI walk/run scales, demonstrating excellent construct validity. This high correlation occurred despite the use of different visual depicters. The PCERT illustrations depict a child stepping up a set of stairs, whereas the OMNI illustrations portray a child walking or running up the slope of a hill. Additionally, the male sex of the pictorial descriptors did not have an impact on perceptual responses because boys and girls did not differ in their ratings of perceived exertion.This study is the first attempt to compare the construct validity of the PCERT and OMNI walk/run scales. The high construct validity is not surprising because both scales are based on Borg's range model of category scaling (1,2) to measure effort perception and each scale includes illustrations of walk or run effort and verbal expressions chosen by children to describe effort. Borg's range model of the three effort continua states that, as exercise intensity increases, there is a linear increase in perceptual (RPE) and physiologic (HR and V̇O2) measures of intensity. Previous research has established the concurrent validity of both scales based on Borg's model of the three effort continua (10,15,17), and the present study confirms these results.In conclusion, we have demonstrated the construct and concurrent validity for both the PCERT and OMNI walk/run scales for assessing effort perception in youth performing a submaximal progressive treadmill test. Perceived exertion using both the PCERT and OMNI walk/run scales increased in a linear manner with increasing exercise intensity. This was the first time that these two scales have been compared, and a high correlation was found between them. At submaximal exercise, the PCERT and OMNI walk/run RPE scales do a similarly acceptable job of assessing perceived exertion in children, and neither scale appears to be superior.This work was supported by NIH grant R01 HD042766 to Dr. James N. Roemmich.REFERENCES1. Borg, G. Perceived exertion as an indicator of somatic stress. Scand. J. Rehabil. 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