Perceived Exertion Scaling Procedures

, Michael GallagherJr.² and Robert J. Robertson³

(1)

Lock Haven University of Pennsylvania, Lock Haven, PA, USA

(2)

University of Central Arkansas, Conway, AR, USA

(3)

University of Pittsburgh, Pittsburgh, PA, USA

Borg has developed and validated two empirical models that explain: (a) psychophysiological interdependence during exercise (i.e., Effort Continua Model) and (b) provide the psychophysical justification for inter-individual comparisons of effort ratings. Borg’s Effort Continua Model describes the functional interdependence of perceptual and physiological responses during exercise. The model provides valuable information regarding the corresponding and interdependent responses of exertional perceptions and underlying physiological mediators as exercise performance intensity increases. Borg’s Range Model predicts that for all clinically normal individuals, there exists corresponding and equal perceptual and physiological/physical response ranges during exercise. This model provides the psychophysical rationale for perceived exertion scaling procedures. There are two types of category scale anchoring: (a) memory procedures and (b) exercise procedures. Memory procedures involve asking the individual to think about the level of exertion perceived during previous PA that they have performed and use this exertional memory to establish their feelings that correspond to the low and high response categories. Exercise procedures involve the individual actually experiencing levels of exertion from a very low to a very high or maximal level and cognitively assigning corresponding low and high scale categories to the intensity of these sensations. The use of both procedures depends on an individual’s previous experience with rating exertional perceptions that varied widely in intensity and mode. The rationale underlying the experimental purpose of the investigation is embedded in the basic tenet of Borg’s Effort Continua Model and Range Model. The primary purpose of this laboratory experiment is to orient an individual to the use of a perceived exertion category metric during aerobic and/or resistance exercise using both memory and exercise scale anchoring procedures.

5.1 Background

5.1.1 Borg’s Effort Continua and Range Models

The rationale underlying Borg’s development of metrics to measure perceived exertion during exercise was based on the concept of the three effort continua: performance, physiological, and perceptual (Robertson 2001). Each continuum represents the individual’s range of possible responses within that specific domain, yet the three continua are closely related. For example, during an aerobic running event, an individual’s performance intensity increases as evidenced by a decrease in minute per mile pace. This increased pace corresponds to increases in both perceptual responses (RPE) and physiological responses, such as HR and VO₂. Knowledge of the functional interdependence of perceptual and physiological responses during exercise can provide valuable information about exercise performance and is the theoretical backbone for applications of RPE research.

The basic tenet underlying the Borg’s Range Model makes inter- and intra-individual comparisons of RPE possible. The model describes how the increase in RPE from a very low to a very high level matches the increase in exercise intensity specific to an individual’s performance capacity (Borg 1998). In other words, the lowest RPE value matches the lowest exercise intensity and the highest RPE value matches maximal exercise intensity. In addition, 50 % of the RPE range corresponds to approximately 50 % of the individual’s exercise intensity range. This holds true whether exercise intensity is expressed in physical units, such as PO, or using a physiological variable such as HR or VO₂. When clinically normal individuals perform exercise at a given intensity, the corresponding level of exertion (RPE) can be compared between clients regardless of aerobic fitness level (Robertson 2004). Likewise, RPE obtained from a single individual can be compared at different time points within an exercise program. If an exercise program results in significant improvements in fitness, the individual’s range of possible exercise intensities has increased. However, the RPE range corresponding to these exercise intensities remains the same. Therefore, a given RPE will be attained at higher exercise intensity as training adaption occurs. This can be seen in clinically normal individuals as well as those with various diseases and disorders for which exercise can be beneficial, such as cystic fibrosis.

The Range Model forms the conceptual basis of the standard, pre-exercise instructions to teach an individual how to use an RPE scale and is crucial to establishing category scale anchoring points. In this application, it is recognized that for all clinically normal individuals the level of perceived exertion corresponding to very low intensity and maximal intensity is the same. Such correspondence of perceptual and exercise intensity ranges provides the psychophysical rationale underlying anchoring procedures for a numerical category scale.

To satisfy the requirements of the Borg’s Range Model, an individual must be able to link the full range of RPE responses with the full range of physiological responses during exercise (Robertson 2004). Therefore, anchoring procedures should be used to ensure that an individual understands this psychophysiological linkage prior to exercise performance in which RPE will be measured or used as a basis for exercise prescription. It is important to note that the scale anchoring procedures be presented on an individual basis because the physiological range required by the exercise task may vary greatly between individuals.

5.1.2 Memory and Exercise Anchoring Procedures

The most practical method of RPE scale anchoring is the memory procedure in which the individual is asked to think about the exertion experienced during previous exercise or physical activity. Using this procedure, the individual is asked to remember when he/she reached levels of exertion equal to the low and high anchor points on the scale. Then, during subsequent bouts of exercise, the individual is asked to rate exertion levels based on memory of exertion at the low and high anchor points. An example of this type of procedure is written into the standard instructions for use of the Adult OMNI-Cycle RPE Scale below.

Following administration of these scaling instructions and anchoring procedures, it is beneficial to ask some simple questions of the individual to determine if he/she understands how to use the scale to rate perceived exertion. Ask the individual to provide an RPE that corresponds to the memory of exertion felt during very light exercise. The individual should respond with a very low number on the scale. If the expected rating is not made, verbally reinforce the individual that perceived exertion is the subjective intensity of effort, strain, discomfort and/or fatigue that is felt during exercise. Ask the individual about various types of exercise or recreational activities he/she performs and what a common RPE value is during those activities. This allows the individual to think about RPE during various exercise intensities that are normally performed during recreation and leisure pursuits. Also, ask the individual to think about and explain the most exhausting exercise he/she has ever performed, and remember the level of exertion experienced during that activity. In this case, if the client rates that activity less than the maximal RPE available on the scale, further explanation of maximal exertion may be necessary.

The second method of RPE scale anchoring is the exercise procedure. In this procedure, the individual actually performs exercise, preferably using the same mode as the exercise test or physical activity program that is to be performed. The scale anchor points, once established, ensure the linkage between perceptual and physiological responses during a specific type of exercise. The exercise anchoring procedure begins after reading the standard instructions for the RPE scale and conducting the memory anchoring procedure. First, the client performs 2 min of exercise at a very low intensity. For treadmill exercise, slow walking would be appropriate; for cycle exercise, unloaded (i.e., zero brake resistance) cycling would be appropriate. For resistance exercise, a very light weight that the subject can lift the specified number of repetitions without any fatigue would be appropriate. The number of repetitions used in a resistance exercise anchoring procedure may vary depending on the exercise test or training program to be performed. At the end of the orientation period, instruct the subject to assign the lowest RPE values (0 or 1 on the OMNI Scale) to the level of exertion experienced at that intensity. Next, the client performs load-incremented exercise (i.e., aerobic or resistance) to maximal intensity, which occurs at the point of volitional termination owing to exhaustion. Begin with the intensity that was previously linked to the lowest RPE on the scale and progressively increase intensity until he/she reaches maximal exercise. Immediately following cessation of exercise, instruct the subject to assign a maximal RPE value (10 on the OMNI Scale) to the level of exertion experienced at that intensity.

A load-incremented exercise protocol that employs standard procedures to determine maximal aerobic power, or maximal oxygen uptake (VO₂max), can also be used to establish the high anchor point for aerobic exercise. VO₂max is defined as the maximum amount of oxygen that can be consumed while breathing ambient air during load-incremented aerobic exercise at sea level. Normally, a graded exercise test (GXT) to measure VO₂max involves 2- to 3-min stages with the test ultimately terminating owing to the subjects inability to continue consequent to fatigue. The length of the exercise stage can be shortened to 30 s or 1 min to quickly progress the individual to a very high intensity.

A load-incremented resistance exercise protocol that employs standard procedures to determine maximal muscle strength, or one-repetition maximum (1RM), can also be used to establish the high anchor point for a category perceived exertion metric such as the OMNI-Resistance Exercise Scale. 1RM is defined as the maximal amount of force that can be produced during a single isotonic contraction of a muscle (group) moving through the full range of joint motion.

5.1.3 Undifferentiated Versus Differentiated RPE and the Dominant Signal

The scale anchoring procedures should separately establish low and high perceptual reference points for the undifferentiated RPE for the overall body and the differentiated RPE for the active limbs and chest/breathing. Rating exertion separately for the chest/breathing (RPE-C), also referred to as respiratory exertion, is appropriate for any type of exercise. In addition, during cycle and treadmill exercise it is appropriate to ask subjects to rate exertion separately for the legs (RPE-L). Other examples of differentiated RPE’s include estimating exertion for the arms (RPE-A) during arm ergometry and the back during rowing exercise.

When performing the exercise anchoring procedures, it is appropriate to choose a primary type of RPE to use in establishing the low and high anchor points. For cycle exercise, RPE-L is representative of the major muscle mass being used during exercise and is often the most dominant signal, showing higher values than RPE-O or RPE-C. Therefore, RPE-L can be used as the primary RPE for exercise anchoring and is presented as such in the laboratory procedures that are presented in this manual. For treadmill exercise, RPE-L may be the dominant perceptual signal compared to RPE-O. However, since walking/running exercise is considered as a weight-bearing, total body activity, RPE-O can be used to establish the anchor points. For resistance exercises, it is appropriate to operationally define a specific differentiated RPE that represents the level of exertion for the active muscle mass (RPE-AM). This RPE may be labeled according to the agonist muscle group, or prime movers, for the specific exercise. For example, differentiated RPE for bench press exercise is specific to the chest/pectoral muscles and should be used to set the scale anchor points.

5.1.4 Exercise Anchoring Procedures and the Perceptual Outlier

It is common practice for clinicians and researchers to orient their clients and subjects using memory anchoring procedures only. However, this is not always appropriate, especially for individuals who may not be familiar with a given type of exercise and may not have experienced exercise intensities across their entire physiological response range. It is not possible to ask someone to remember a level of exertion experienced at certain exercise intensity if they have never performed that intensity. For example, asking a child or sedentary adult to assign a maximal RPE value to the memory of the most difficult exercise ever performed would not be appropriate if they had never performed maximal exercise. Therefore, memory anchoring followed by exercise anchoring is most appropriate in these individuals.

It is important to note that, even for extremely active and/or fit individuals, rating perceived exertion is a learned skill (Robertson 2004). Physical activity and fitness levels may not determine one’s ability to rate perceived exertion accurately across the full physiological and performance range. Individuals who rate perceived exertion inappropriately and whose responses do not conform to the Borg’s Range Model are termed as perceptual outliers. Some individuals tend to augment RPE, or provide higher RPE values than expected relative to the measured physiological response (Fig. 5.1, client A). They may even report a maximal RPE when performing submaximal exercise intensity. Likewise, some individuals tend to reduce RPE, or provide lower RPE values than expected relative to the measured physiological response (Fig. 5.1, clients B and C). They may assign a submaximal RPE to maximal exercise intensity. Perceptual reducers seem to be more common than perceptual augmenters, especially among young recreationally active adults. Therefore, the combination of memory and exercise anchoring procedures is recommended for all individuals who are not experienced with RPE procedures in order to identify perceptual outliers who require additional practice, feedback and reinforcement.