The OMNI Perceived Exertion Scale was initially validated for use by female and male children (6–12 yr old) performing progressively incremented cycle ergometer and treadmill (walking/running) exercise (9,10,14). Recently, a mode specific pictorial format of the OMNI Scale has been validated for adults performing upper and lower body resistance exercise (12). In addition, concurrent and construct validity of the OMNI-Cycle Scale of Perceived Exertion was demonstrated in young adult men and women (11). However, the adult format of the OMNI Perceived Exertion Scale has not undergone concurrent and construct validation for use during weight bearing aerobic exercise. An important application of the adult format of the OMNI Perceived Exertion Scale is to use the perceptual responses to guide the progression of a graded exercise test in either a health/fitness and/or clinical setting. Therefore, the OMNI scale validation for incremental treadmill exercise was the primary focus of the present investigation.
Previous research with the core format of the adult OMNI Scale employed a cyclist (11) and a “weight lifter” (12). It is not known to what extent the core format of the OMNI Scale can be used to assess exertional perceptions of adults engaged in dynamic exercise modes where the pictorial depicts walking or running. Considering that evidence is not available for cross-modal application of the adult OMNI Scale (i.e., estimating RPE using cycle pictorials while performing walking/running exercise) necessitates the independent and mode specific validation of the OMNI-Walk/Run Scale.
The possible role of the subject’s gender in mediating the intensity of RPE has been evaluated in previous research (6,9,13). Given that gender differences in RPE may be important in both the practical application and future research of perceptual responses, it is important to establish that the OMNI-Walk/Run Scale is valid for use by both women and men performing walking/running exercise. Both the weight lifting and cycling pictorial format of the adult OMNI Scale have been validated separately for adult women and men (11,12). However, gender specific validation of the OMNI-Walk/Run Scale for adults has not been undertaken. Based on previous research with adult OMNI Scales (11,12), it was expected that the walking/running pictorial format of the OMNI Scale would be valid for separate samples of adult women and men performing incremental treadmill exercise.
The present investigation examined concurrent and construct validity of the OMNI-Walk/Run Scale of Perceived Exertion (Fig. 1) separately for adult women and men. Evidence of response validity was accepted according to the following hypotheses: (a) RPE derived from the OMNI- Walk/Run Scale would distribute as a positive linear function of submaximal oxygen uptake (V̇O2), relative maximal oxygen uptake (%V̇O2max), ventilation (V̇E), respiratory rate (RR), respiratory exchange ratio (RER), and heart rate (HR) responses for separate groups of young adult women and men; and (b) RPE derived from the OMNI-Walking/Running and Borg Scales during incremental walking/running exercise would be positively correlated.
Sixty-seven healthy men and women ranging in age from 18 to 36 yr volunteered as subjects. Their descriptive characteristics are presented in Table 1. Subjects did not present any clinical, neuromotor, or cognitive contraindications to exercise testing. Informed consent was obtained from each subject, and the experimental protocol was approved by the Human Subjects Review Board at Appalachian State University and Western Kentucky University. The experimental procedures were in accordance with the policy statements of the American College of Sports Medicine.
This investigation used a perceptual estimation paradigm administered during a single, graded exercise test (GXT) on a treadmill. The Bruce GXT protocol was employed for both the men and women for the determination of maximal oxygen uptake (V̇O2max) (4). All subjects were tested in a 3-h postprandial state and were requested not to consume alcohol or participate in vigorous physical activity during the 24-h period preceding each trial.
Both concurrent and construct paradigms were used to establish measurement validity of the adult OMNI-Walk/Run Scale (RPE-OMNI). A concurrent validation paradigm employs a two variable scheme: (a) criterion (i.e., stimulus) variable, and (b) concurrent (i.e., response) variable. In the present investigation, V̇O2, %V̇O2max, V̇E, RR, RER, and HR responses to the treadmill protocol served as the criterion variables. The RPE-OMNI for the overall body was the concurrent variable. Evidence of concurrent validity was taken as a positive correlation between criterion and concurrent variables when examined over the full perceptual-physiological range.
Construct validity was established by correlating RPE derived from the OMNI-Walk/Run Scale with RPE from the 1982 version of the Borg (6–20) Scale (RPE-BORG) (2). In this paradigm, RPE was the construct variable. The Borg Scale was the criterion metric and the OMNI-Walk/Run Scale the conditional metric. A high validity coefficient demonstrates that the conditional metric measures the same perceptual construct as the criterion metric.
Body mass (kg) and height (cm) were determined using a Detecto-Medic Scale and attached stadiometer (Detecto Scales Inc., New York). Percent body fat was estimated from skinfold measurements taken three sites (triceps, subscapular, and abdomen) using the procedures of Lohman (5). Skinfolds were measured three times at each site to the nearest 0.5 mm with the mean value recorded. All skinfold measurements were taken on the right side of the body. Two different skinfold assessors were used (one from each institution) each were highly trained and experienced in measuring skinfolds.
Cardiorespiratory and aerobic metabolic measures.
Oxygen uptake (V̇O2) and ventilation (V̇E) were measured using the MedGraphics CPX Express (MedGraphics Corporation, St. Paul, MN) and the Vacu-med Vista mini-cpx (Vacu-med Corporation, Ventura California) metabolic systems. Gas calibration was conducted before each GXT. Heart rate was measured using a Polar Monitor System (Polar Electro Inc., Woodbury, NY) and the highest observed heart rate was recorded as maximal heart rate. V̇O2, V̇E, respiratory rate (RR), respiratory exchange ratio (RER), heart rate (HR), and RPE measurements were made every min throughout the GXT.
Rating of Perceived Exertion.
An undifferentiated rating was estimated for the overall body using both the 1982 version of the Borg (6–20) Perceived Exertion Scale (RPE-BORG) and the OMNI-Walk/Run Scale (RPE-OMNI) (Fig. 1). A standard definition of perceived exertion and separate instructional sets for the Borg and OMNI Scales were also read to the subject immediately before the exercise test. The Borg and OMNI scales were separately viewed by the subject when their respective instructional set was read. Both scales were anchored using a combination of exercise (13) and memory (10) procedures. This procedure requires the subject to cognitively establish a perceived intensity of exertion that is consonant with that depicted visually by the figure walking at the bottom (i.e., low anchor, rating 0) and top (i.e., high anchor, rating 10) of the hill as presented in the OMNI-Walk/Run Scale illustrations. As a mouthpiece prohibited a verbal rating response, subjects pointed to their RPE on the scale. The OMNI-Walk/Run and the Borg Scales were in full view of the subject at all times during testing. In a counter-balanced manner, subjects were asked to point to their RPE on either the OMNI-Walk/Run or the Borg Scale. After the first RPE was obtained from either scale, within 10 s the subjects were asked to rate their perceived exertion from the remaining scale.
For both scales, perceived exertion was defined as the subjective intensity of effort, strain, discomfort and/or fatigue that was felt during exercise (8). The instructional set for the 15-category Borg Scale has been published previously (13). The instructions for the OMNI Scale were as follows:
We would like you to walk and then run on a treadmill. Please use the numbers on this scale to tell us how your body feels when walking or running. Look at the person at the bottom of the hill who is just starting to walk. If you feel like this person when you are walking, the exertion will be Extremely Easy. In this case, your rating should be a number zero. Now look at the person who is exhausted at the top of the hill. If you feel like this person when walking/running, the exertion will be Extremely Hard. In this case, your rating should be a number 10. If you feel somewhere between Extremely Easy (0) and Extremely Hard (10) then give a number between 0 and 10. We will ask you to point to a number that tells how your whole body feels including your legs and breathing. Remember, there are no right or wrong numbers. Use both the pictures and words to help you select a number. Use any of the numbers to tell how you feel when walking or running.
Descriptive data for perceptual and physiological variables were calculated as mean ± SD. An independent t-test was used to evaluate gender differences in physiological variables during maximal exercise (Table 1). A two-way repeated measures ANOVA (sex) × (intensity) was used to analyze RPE-OMNI, RPE-BORG, and selected physiological variables throughout the exercise test. Significant intensity main effects (exercise stage) were evaluated with paired t-tests. Significance was set at P < 0.05 for all variables in the analysis.
Evidence for both concurrent and construct validity was determined using linear regression analysis with repeated measures over intensity. When testing concurrent validity, the analysis separately regressed physiological parameters: %V̇O2max, V̇E, HR, RR, and RER against RPE-OMNI and RPE-BORG. For these analyses, a repeated measures paradigm was used where data from the last 15 s of stages 1–4 were obtained for each subject to form the dependent and independent variables. This procedure yielded the greatest number of data points for the analyses (82.1% of the subjects had complete data for all variables at the end of stage 4 vs 52.2% for the end of stage 5). Five different models were created for each measure of RPE. Regression coefficients were calculated separately for the female and male groups. When testing construct validity, the analysis regressed RPE-OMNI against RPE-BORG using data from each of the last 15 s of stages 1–4. To minimize Type 1 error associated with multiple correlational analysis involving the same subjects, the level of statistical probability for all regression coefficients was set at P < 0.01.
Listed in Table 1 are the means ± SD for the physiological responses at maximal exercise intensity in addition to the subject’s descriptive characteristics. The sample consisted of 33 men and 34 women. Significant differences were found between genders for height, weight, percent body fat, absolute and relative V̇O2, HR, and V̇E.
Listed in Table 2 are the means ± SD for both RPEs and selected physiological variables during submaximal exercise for the men and women subjects. Significant interactions were found for all variables listed (P < 0.001) with the exception of RER: (F (4,128) = 0.83, P = 0.51) A significant intensity main effect was found for all variables listed at P < 0.001. Significant increases were found for both RPEs and physiological variables throughout the GXT for both the men and women, respectively. Throughout the GXT, 77.8% of men completed the fifth stage, and were exercising at an intensity equivalent to or greater than 96.0 ± 4.0% of V̇O2max. In addition, 65% of the women completed the fourth stage, and were exercising at an intensity equivalent to or greater than 91.7 ± 15.5% of V̇O2max. Because of the need to examine scale validity over the widest possible perceptual-physiological range, data were analyzed over the first five stages of the GXT for both genders in Table 2.
Concurrent Validity: OMNI-Walk/Run Scale
Regression analysis indicated that for both the men and women, the ratings from the RPE-OMNI and RPE-BORG distributed as positive linear function for %V̇O2max, V̇E, HR, RR, and RER. Listed in Table 3 are the correlation coefficients and linear regression analyses for these functions presented by gender. All regression functions were statistically significant (P < 0.01).
Construct Validity: OMNI-Walk/Run vs Borg Scales
Regression analysis indicated that for both the men and women subjects, the ratings from the OMNI-Walk/Run RPE Scale were positively and linearly related to Borg RPE Scale throughout the GXT. Listed in Table 4 are the correlation coefficients and linear regression analyses for these functions. All regression analyses were statistically significant (P < 0.01).
The walking/running pictorial format of the OMNI Scale of Perceived Exertion was validated using both a concurrent and construct paradigm for separate groups of young adult women and men. Validation criteria stipulated that during treadmill exercise that progressed from walking to running, (a) RPE derived from the OMNI-Walk/Run Scale would distribute as a positive linear function of %V̇O2max, HR, V̇E, RR, and RER responses for separate groups of young adult men and women and (b) RPE derived from the OMNI- Walk/Run and Borg Scales would be positively correlated.
Various concurrent paradigms employing selected respiratory-metabolic variables as criterion measures have been accepted as a standard procedure when validating RPE category scales (8,10,11). Response linearity held for the exertional responses when examined separately for both the men and women subjects. Validity coefficients derived from the various regression models ranged from r = 0.67 to 0.88.
The strong positive relation between the OMNI-Walk/Run RPE and selected respiratory-metabolic variables is consistent with a recent investigation which used a concurrent paradigm to validate the OMNI-Cycle RPE Scale in adult women and men (11). Another recent experiment to establish concurrent validity of the adult format of the OMNI perceived exertion scale was completed with resistance exercise pictorials (12). Strong positive and linear regression models were observed between total weight lifted and the RPE for both the active muscles and overall body (r = 0.79–0.91). In addition, OMNI Scale RPE (Active Muscles) was highly correlated (r = 0.87) with blood lactic acid concentration sampled during biceps curl exercise.
The linear regression models derived in the present investigation are consistent with those reported by Roberston et al. (11) when using the OMNI-Cycle Scale. In that study where V̇O2 and HR were used as criterion variables, linear regression coefficients ranged from r = 0.81 to 0.95 for both the undifferentiated (RPE-Overall) and differentiated (RPE-Chest and RPE-Legs) exertional signals. When examining the relation between overall OMNI-Walk/Run RPE and %V̇O2max we found an r2 = 0.72 and 0.74 for women and men, respectively. This finding is consistent with the results of the OMNI-Cycle Scale reported by Robertson et al. (11): r2 = 0.77 and 0.89 for women and men, respectively. In addition to the significant regression models found in the present investigation for %V̇O2max and HR, strong positive relationships were also found for V̇E, RR, and RER (Table 3).
The use of RPE response linearity (i.e., positive) as an applied validation criterion is consistent with the basic tenants of Borg’s Effort Continua Model (1,10). This model indicates that as exercise performance increases along an intensity dependent continuum there are corresponding and interdependent increases in response intensity along perceptual (i.e., RPE) and physiological (i.e., V̇O2, HR,V̇E, and RR) continua, demonstrating a positive relation. The positive linear relation observed in the present study between OMNI-Walk/Run Scale RPE responses and selected physiological variables is consistent with the application outcomes underlying the Effort Continua Model.
A secondary purpose of the present investigation was to establish concurrent validity of the OMNI-Walk/Run Scale separately for the men and women samples. When examining each gender independently, strong positive regression coefficients were found for both men and women. These findings are consistent with previous reports of gender specific validity of the OMNI perceived exertion scale for both children and adults performing cycle (10,11), treadmill (9,14) and resistance (12) exercise. Gender specific validation is important given recent research interest in selected physiological mediators that may explain similarities and/or differences in RPE between women and men (6,7,13).
Construct validity of the OMNI-Walk/Run Scale was established using the 1982 version of the Borg (6–20) Scale as the criterion metric. It was hypothesized that RPE derived from the OMNI-Walk/Run Scale would be positively correlated with Borg Scale RPE when perceptual estimates from both metrics were obtained during the walking/running treadmill exercise protocol. The findings of the present investigation supported this hypothesis, establishing construct validity of the OMNI-Walk/Run Scale. Validity coefficients between perceptual responses obtained from the two category scales were 0.96 for both the males and females. These results are consistent with those of the adult version of the OMNI-Cycle Scale in which the validity coefficients ranged from 0.92 to 0.97 for RPE-Overall, RPE-Legs and RPE-Chest (11).
The comparatively high level of construct validity observed presently indicates that the OMNI-Walk/Run Scale measures the same properties of an exertional precept as does the Borg (6–20) Scale when assessments are made for young adult women and men performing graded exercise tests. Based on concurrent paradigms, the Borg (6–20) Scale is generally considered a valid metric to assess exertional perceptions over a wide range of exercise modes and metabolic rates (3). Validity of the OMNI-Walk/Run Scale over a wide stimulus-response range (i.e., walking progressing to running) is necessary in exercise testing, prescription and intensity self-regulation where it is expected that metabolic rate will fluctuate from low to high levels.
The findings of the present investigation provide both concurrent and construct evidence supporting use of the OMNI Scale by adult women and men to estimate RPE during graded exercise testing. The critical importance of concurrent validity was demonstrated by the OMNI-Walk/Run Scale in that RPE responses increased in a concurrent manner with V̇O2 and HR, which is consistent with Borg’s Effort Continua Model. Construct validity was established by determining that the OMNI-Walk/Run Scale measures the same perceptual construct (i.e., RPE) as a previously validated criterion scale. This validity evidence broadens the scope of application of the OMNI perceived exertion pictorial system. When examining the presently validated walking and running and the previously validated cycle exercise formats of the Adult OMNI Scale, RPE based exercise evaluation is possible for both weight bearing and nonweight bearing aerobic modes.
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