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00005768-201305000-0002600005768_2013_45_1012_lemay_individualized_5editorial< 91_0_13_4 >Medicine & Science in Sports & Exercise©2013The American College of Sports MedicineVolume 45(5)May 2013p 1012–1017Interest of an Individualized Score among Children Using the OMNI Cycle Scale[APPLIED SCIENCES: Commentary]LEMAY, VALERIE1,2; O’LOUGHLIN, JENNIFER3; TREMBLAY, ANGELO4; MATHIEU, MARIE-EVE1,21Department of Kinesiology, University of Montreal, Montreal, QC, CANADA; 2HUC Sainte-Justine Research Center, Montreal, QC, CANADA; 3University of Montreal Hospital Center Research Center, Montreal, QC, CANADA; and 4Department of Kinesiology, Faculty of Medicine, Laval University, QC, CANADAAddress for correspondence: Marie-Eve Mathieu, Ph.D., Département de kinésiologie, Université de Montréal, Bureau 8223, CP 6128, Succursale centre-ville, Montréal, Québec, Canada H3C 3J7; E-mail: me.mathieu@umontreal.ca.Submitted for publication June 2012.Accepted for publication October 2012.ABSTRACTPurpose: The study purposes were 1) to study the differences between perceived exertion measured by a generic (/10) or an individualized (/max value obtained during the test) score on the OMNI cycle scale (OMNImax and OMNI10) and the actual effort (peak oxygen consumption) at different stages of a maximal cycling test in a group of children age 8 to 10 yr old and 2) to assess whether the concordance between perceived exertion and actual effort differs according to body mass status or physical activity level.Methods: A total of 477 children from the QUebec Adipose and Lifestyle InvesTigation in Youth (QUALITY) cohort performed a progressive maximal test on a cycling ergometer. Oxygen consumption was continuously measured during the test. Perceived exertion was measured at the end of each stage, at exhaustion, and during recovery using the OMNI cycle scale. Percentage of peak oxygen consumption was compared with %OMNI10 and %OMNImax; two-way ANOVA was conducted to detect the differences between the physiologic and subjective indicators of exercise intensity according to body mass status and physical activity levels of children.Results: At each stage of the test, except during recovery, children perceived their effort to be lower than the actual intensity level. This lower scoring of exercise intensity is more important when using OMNI10 than OMNImax. No differences in body mass status or physical activity level were observed.Conclusion: It is better to consider the OMNI score relative to the maximal score obtained (OMNImax) from the children to reflect the actual physiological effort (oxygen consumption). The association between the effort performed and the OMNI cycle scale score is independent of body mass status and physical activity level of the child.Numerous activity intensity indicators, including speed, power output, heart rate (HR), oxygen consumption (V˙O2), and lactatemia (21), are used to quantify the level of effort during physical activity in the laboratory. In real life settings, the objective evaluation of effort intensity is often limited by the lack of equipment, time, and/or qualified personnel. The perceived exertion scale is a noninvasive tool that subjectively rates perceived exertion (RPE), which is a psychophysiological measure that is defined as “a subjective intensity of effort, strain, and/or discomfort experienced during exercising” (27). The RPE can guide cardiovascular testing and help to determine the maximal effort (5). The RPE is easy to use and facilitates exercise prescriptions; instead of providing the %HR or %V˙O2 to be maintained, a RPE zone can be indicated (5,21,27), even in children (11).The Borg scale, which ranges from 6 (no exertion at all) to 20 (maximal exertion), is the most commonly used perceived exertion scale (2,23). Although it has been validated in adults (4,7,31), some researchers believe that the Borg scale may not be appropriate for children (28,32) because they may not have the vocabulary or cognitive capacity to properly interpret the intensity descriptors that are used in the adult scales (8,10,25). Consequently, scales with pictograms have been designed for use in younger populations; among these scales, the OMNI scale (Fig. 1) is one of the most frequently used, according to recent PubMed searches. The OMNI scale was first validated in children using cycling ergometers and treadmills (24,25). The OMNI scale pictograms depict a child or adult performing a physical activity and becoming increasingly more exhausted. The exhaustion level is rated on a scale from 1 to 10. Unlike the Borg scale, in which intensity of effort is described, the OMNI scale relates directly to fatigue (25). Several studies have reported the validity of different versions of the OMNI scale in subjects who perform graded submaximal or maximal tests. The perceived exertion and physiological parameters (i.e., V˙O2 and HR) are measured at different stages of the test. There is evidence of both concurrent validity (i.e., positive linear associations RPE at each stage and physiological measurements) and construct validity (positive associations between RPE from different scales) for the OMNI scale (1,22,25,26).FIGURE 1. OMNI scale of perceived exertion: child, cycle format (Robertson RJ, Goss FL, Boer NF, Peoples JA, Foreman AJ, Dabayebeh IM, et al. Children’s OMNI scale of perceived exertion: mixed gender and race validation. Med Sci Sports Exerc. 2000;32(2):452–8 (used with permission)).One limitation of previous studies is that work intensity is reported only as a function of the absolute value of V˙O2, watts, or HR. It is unknown if relative intensity measured objectively corresponds to relative intensity measured subjectively using the OMNI scale and this, when stages are expressed as a function of relative intensity (i.e., a percentage of the maximal value obtained during the test). Only Roemmich et al. (29) graphically illustrated the relationship between the OMNI-RPE and relative effort in children age approximately 11 yr who walked or ran. In the Roemmich study, the percentage of the RPE scale is always inferior to the percentage of the relative intensity, which is expressed as a function of V˙O2 or HRmax. The relationship between the RPE (measured using the OMNI cycle scale) and relative effort remains to be thoroughly investigated. It is also known that children do not reach the highest score of the RPE scale when they perform maximal work (1). Therefore, a score that considers the individual maximal score would warrant investigation.Factors such as body mass status and physical activity level might influence the concordance between perceived exertion and physiological parameters. In a validation study of the CERT scale in children age 10 yr (on average), Marinov et al. (17) observed that a higher body mass index (BMI) corresponded to a higher mean RPE during a progressive maximal effort test. Similar results were obtained in a second study in which obese children had higher RPE than children with healthy BMI for standardized workloads (19). No such study has been conducted using the OMNI scale. To our knowledge, no reports have assessed whether the level of physical activity affects the OMNI scores in children. We hypothesized that less active children, who are not used to exerting physical effort, perceive an exercise of a relative intensity as more demanding than active children. Currently, the OMNI cycle scale has not been validated in children taking into account either body mass status or physical activity level.This study had two objectives: 1) to study the differences between the perceived exertion measured by a generic (/10) or an individualized (/max value obtained during the test) score on the OMNI cycle scale (i.e., OMNImax and OMNI10) and the actual effort (peak oxygen consumption) at different stages of maximal cycling tests and during the recovery periods in a group of children age 8 to 10 yr old, and 2) to assess whether the concordance between perceived exertion and actual effort differs according to body mass status or physical activity level.METHODSThe data were obtained from QUALITY (QUebec Adipose and Lifestyle InvesTigation in Youth) (15), which is a longitudinal cohort study of the natural history of pediatric obesity, its determinants, and its cardiometabolic consequences. The cohort includes 632 Caucasian children of Western European ancestry ranging in age from 8 to 10 yr old at the first visit and who have at least one obese biological parent (BMI >30 kg·m−2 or waist circumference >100 cm for men and 88 cm for women). Children with type 1 or 2 diabetes or a serious illness, psychological condition, or cognitive disorder that hindered participation in the study or who had taken antihypertensive medication or steroids (except if administered topically or through inhalation) or were on a very restricted diet (approximately 600 kcal·d−1) were excluded. The inclusion criteria for this current study included the following factors: 1) completed a maximal cycling test attaining an HR ≥195 bpm or a respiratory exchange ratio ≥1, 2) performed the cycling test using the protocol for children <160 cm (a different protocol was used for taller children), and 3) each cycling stage selected lasted ≥1 min. A total of 478 of 632 children were qualified for the study. For the analyses, including the physical activity level, 408 children who had worn an accelerometer ≥4 of 7 d for >10 h·d−1 were included. The data were collected at the Sainte-Justine Hospital University Center in Montreal and at Laval Hospital in Quebec. The ethics committees from these centers approved the project. The parents of the study participants provided written informed consent.Body composition.Anthropometric measurements were taken according to standard procedures; the children wore light clothing and no shoes. The children were weighed on an electronic scale (0.1-kg precision; Montreal site: Cardinal Detecto, 758C Series, Cardinal Scale Manufacturing Co., Webb City, MO; Quebec site: Tanita TBF-300A, Arlington Heights, IL) and measured with a stadiometer (0.1-cm precision; Montreal site: Ibiom, modèle 600, Ibiom Instruments Ltée, Sherbrooke, Québec, Canada; Quebec site: SECA modèle 216, Medical Scales and Measuring Devices seca corp., Hanover, MD). The body fat percentage was determined using a dual-energy x-ray absorptiometry (Prodigy Bone Densitometer System, DF+14664; GE Lunar Corporate, Madison, WI). BMI was calculated, and the children were categorized into one of three body mass status groups according to percentiles from the Centers for Disease Control and Prevention Clinical Growths Charts for children ≥2 yr old (14) and Canadian guidelines: normal (<85th age- and sex-specific percentile), overweight (≥85th and <95th), and obese (≥95th) (16).Aerobic capacity.A maximal test on a cycling ergometer (Montreal site: Ergoline, ER900, Bitz, Germany; Quebec site: Ergoline, Ergoselect 100K, Bitz, Germany) was performed with measures of gas exchange to evaluate the peak oxygen consumption (V˙O2peak) (Montreal site: Jaeger, Oxycon Pro, Viasys Healthcare, Germany; Quebec site: Quark b2, Cosmed, Italy). The starting power output was 25 W. The protocol for children <160 cm was adapted from the McMaster protocol (12) and used the following criteria: 2-min stages with an increase of 25 W at each stage until exhaustion. Only the second stage lasted 5 min. The children were asked to maintain a pedaling rate of 40–70 rpm. When the children could not maintain the required rate (<40 rpm) or when they requested to stop the exercise, they entered a recovery period of 2 min at 25 W. Gas and volume calibrations were conducted before each test. Breath-by-breath data were averaged over a 30-s interval to determine the V˙O2peak. HR was measured throughout the test using electrocardiography.Physical activity.Physical activity was objectively determined using accelerometry (ActiGraph LS 7164 activity monitor; ActiGraph LLC, Pensacola, FL). The accelerometer was worn for 7 d after the evaluation visit. The children who met the Canadian recommendation of >11,000 steps a day, which corresponds to 60 min of physical activity per day, were classified as “active” (3,13).Perceived exertion.During the last 30 s of each 2- or 5-min cycling stage, the children were asked to indicate the intensity of their effort using the OMNI scale according to the protocol proposed by Robertson et al. (25), including the anchoring technique. Assessment during recovery was performed at 1 min posttest. The English version of the OMNI cycle scale was translated into French using a forward–backward translation method. The %OMNI10 score was calculated by dividing the OMNI scores (reported at each stage) by the maximal scale value (i.e., 10) multiplied by 100. As previously mentioned, children do not always reach the highest score of the RPE scale when they perform maximal work (1). Therefore, we developed an alternative score that reflected an individual’s profile: %OMNImax was calculated by dividing the OMNI score at each stage by the score reported at the maximal level of exhaustion. To analyze the influence of body mass status and physical activity level on the OMNI ratings, the concordance between the perceived and real effort was calculated at each stage of the test. Concordancemax was computed by subtracting %OMNImax from %V˙O2peak. Concordance10 was computed by subtracting %OMNI10 from %V˙O2peak. For example, a child with a V˙O2peak of 1795 L·min−1 who scored 2 on the OMNI scale for a given stage where he was at 1097 L·min−1 of V˙O2 would have a concordance10 of (2 / 10 × 100) − ((1097 / 1795) × 100) = −41%. Considering that the maximal score expressed during the test was 8, the concordancemax for the same stage would be (2 / 8 × 100) – (1097 / 1795 × 100) = −36%.A one-way ANOVA was used to investigate the various intensity indicators. We compared the two subjective indicators of intensity (%OMNI10 and %OMNImax) to the physiological indicator (%V˙O2peak or %HRmax) at each stage of the incremental testing protocol (25 to 125 W and during recovery period). The Tukey–Kramer post hoc test was used to identify the significant differences among the subjective and physiological indicators. Two-way ANOVA was performed to assess concordancemax and concordance10 at each stage (25, 50, 75, 100, and 125 W, at maximum watts (Wmax) and during recovery—25 W), with body mass status (healthy body mass, overweight, or obese) as the first factor and physical activity group (active or less active) as the second factor. The level of statistical significance was set at 0.05. The analyses were performed with JMP statistical software (version 9.0.2; SAS Institute, Cary, NC).RESULTSThe descriptive characteristics are presented in Table 1. At intensities ranging from 25 to 125 W and during recovery, a statistically significant difference was observed between the real (%V˙O2peak) and perceived intensity for both %OMNImax and %OMNI10 (Fig. 2). At low intensity (25 W), there was no advantage to using %OMNImax or %OMNI10. However, from 50 to 125 W, there was a statistically significant difference between the indicators; the %OMNImax values were closer to the %V˙O2peak values compared with the %OMNI10 values. At the maximal power output attained during the test (Wmax), there was a statistically significant difference between %V˙O2peak and %OMNI10 values but not between %V˙O2peak and %OMNImax values. When using OMNImax during recovery, children rated the intensity of effort higher; with OMNI10, they rated it lower. Results obtained with %HRpeak were similar to those obtained with %V˙O2peak, except at recovery where %HRpeak is significantly higher than the OMNI scores, whereas %V˙O2peak was significantly lower than OMNI scores (Fig. 3).TABLE 1 Selected characteristics of study participants (n = 477).FIGURE 2. Physiologic and subjective indicators of exercise intensity—aerobic capacity.FIGURE 3. Physiologic and subjective indicators of exercise intensity—HR.No statistically significant differences were observed in any of the analysis (25 W to 125 W at Wmax or during recovery at 25 W) concerning the influence of body mass status and physical activity level using either concordancemax or concordance10.DISCUSSIONThe purpose of this study was to determine whether children age 8 to 10 yr assess with precision the intensity of their effort during a cycle ergometer test on the OMNI scale and to determine whether body mass status or physical activity level influenced perceived level of exertion. The children rated the intensity of their effort as being lower than it really was, especially at low intensity. %OMNImax was closer to physiological values than %OMNI10. Perceived exertion on a cycle ergometer did not differ among children with various body mass statuses and physical activity levels.This study is the first to consider that children often do not reach the maximal score on an RPE scale by computing a percentage of the maximal score reached (%OMNImax). In a study of the validity of RPE scales, Barkley and Roemmich (1) observed that at exhaustion, children expressed RPE scores that corresponded to 75% ± 20% and 74% ± 19% of the maximal values of the Cart And Load Effort Rating (CALER) and OMNI scales, respectively. In the current study, the children reached an average maximal score of 7.9/10, a value close to that reported by Barkley and Roemmich (1). The authors (1) suggested that children were not familiar with exerting maximal effort in this manner and did not have all of the perceptual memory anchors needed to achieve maximal scores on the RPE scales. The authors advanced the idea that children might have thought that because they were still turning the pedals, they were not at maximal effort. Repeated exposure to exercise sessions might improve children’s interpretation of the scale as well as the correlation between the physiological and subjective intensity indicators (20).Percentage OMNImax was closer to %V˙O2peak than %OMNI10. Therefore, it may be necessary to adjust the target RPE values as a function of each child’s maximal score when the perceived level of exertion is used to indicate intensity during exercise sessions. However, this implies a priori the achievement of an effort test. Note that the results from the current study reflect a single exposure to an effort test and the OMNI scale. Moreover, the results of this study pertain to a cycling ergometer test, which is a non–weight-bearing activity. The validity of the OMNI scale in French must still be studied. In addition, the concordance of the OMNI scores with the physiological measures from other exercises, such as walking and running, and other testing protocols remains to be investigated.According to Dupuis et al. (6), the psychomotor capacities of obese children might be affected by body mass status; therefore, their perceived exertion levels could be increased. For all stages of the cycle ergometer test in our study, there was no difference in perceived exertion levels in children with different body mass status. Because the prevalence of overweight and obese children is high (30), it is important that tools such as the OMNI are well adapted for use in this subgroup. Our data support the use of OMNI cycle scale in children regardless of body mass status.No differences were observed at any stage between the children who met the physical activity practice guidelines and those who did not. We hypothesized that less active children would have higher RPE values for a given intensity because they are not accustomed to physical exertion. This was not the case, and it could reflect the ability of children to report their level of strenuousness accurately or support the adaptability of the scale to obtain exertion levels in children regardless of their physical activity level. The OMNI scale may help with the prescription of exercise intensity which intensity is a key component of physical activity guidelines. In fact, children should accumulate at least 60 min of moderate-to-vigorous intensity physical activity daily (3). Furthermore, body mass and physical activity level do not influence the perceived level of exertion, which makes the OMNI scale even more valuable for use in a large population of children.According to Morgan (19), approximately 66% of the variance in perceived exertion is explained by physiological determinants, and the balance is related to psychological factors. Although directly related, it is likely unrealistic to expect perfect agreement between the RPE and physiological markers. Some researchers have developed a curvilinear scale for children (9), which assumes that the relationship between RPE and work intensity is not linear. According to these authors, because ventilation increases rapidly above a work rate of 60%V˙O2max, the RPE might also increase quickly. Using this curvilinear scale, children report 96% of the maximal scale value at exhaustion, which suggests that a curvilinear relationship might be more appropriate in children, particularly considering their cognitive development. When a maximal effort test is not possible (thus, the use of OMNImax is also not possible), the Eston–Parfitt curvilinear RPE scale (9) may be a more appropriate tool.In conclusion, using the OMNI scale, children underestimate the intensity of their effort during a cycling test. Body mass and physical activity levels do not influence the concordance between the real (%V˙O2peak) and perceived intensity (%OMNI) of exercise. Considering the maximal RPE score when comparing %OMNI to %V˙O2peak values, %OMNImax appears to be a good strategy for obtaining the most precise subjective estimate of exercise intensity.The authors thank the QUALITY research team and its participants. Dr. Marie Lambert (July 1952 to February 2012), pediatric geneticist and researcher, initiated the QUALITY cohort. Her leadership and devotion to QUALITY will always be remembered and appreciated. The QUALITY study was supported by the Canadian Institutes of Health Research, the Heart and Stroke Foundation of Canada, and the Fonds de la recherche en santé du Québec.This work is also partially supported by a grant from the Fondation des étoiles and HUC Sainte-Justine Foundation. Jennifer O’Loughlin holds a Canada Research Chair in the Early Determinants of Adult Chronic Disease.The authors declare no conflicts of interest.The results of the present study do not constitute endorsement by the American College of Sports Medicine.REFERENCES1. Barkley JE, Roemmich JN. Validity of the CALER and OMNI-bike ratings of perceived exertion. Med Sci Sports Exerc. 2008; 40 (4): 760–6. [CrossRef] [Full Text] [Medline Link] [Context Link]2. Borg GA. Psychophysical bases of perceived exertion. 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OMNI Cycle ScaleLEMAY, VALERIE; O&#8217;LOUGHLIN, JENNIFER; TREMBLAY, ANGELO; MATHIEU, MARIE-EVEAPPLIED SCIENCES: Commentary545