1984; 64:343-346.PHYS THER. Susan B O'SullivanPerceived Exertion : A Review

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Perceived Exertion A Review SUSAN B. O'SULLIVAN

Physical therapists are well aware of the physiological responses to exercise. The process by which these underlying mechanisms contribute to the perceptual response of perceived exertion is generally less familiar. The purpose of this article is to summarize briefly some of the current major concepts about perceived exertion and to indicate, where possible, the potential significance of these concepts for physical therapy.

Key Words: Exercise test, Exertion, Physiology.

Interest in physical conditioning for preventative and re-habilitative purposes has prompted an increased interest in understanding the physiological stresses of prolonged work. Concurrent with this has been an increased awareness of the psychological factors and the perceptions associated with pro-longed work. Perceived exertion has been defined as the subjective rating of the intensity of physical work and has been the subject of increasing attention in the literature since the late 1950s.1 The processing of sensory cues related to physical performance enables an individual to perceive gen-eral feelings of exertion and more specific sensations of phys-iological performance such as shortness of breath, muscular effort, and joint pain. Borg suggests that the overall perception of exertion is a "gestalt" of many feelings and sensations related to the performance of work.2

The purpose of this article is to summarize the literature on perceived exertion and to discuss the therapeutic implica-tions for physical therapy.

PSYCHOPHYSICAL RATING SCALE

The scientific study of perceived exertion and work inten-sity first concentrated on the development of methods to establish perceptive estimation of work using a ratio scale. The original work of Stevens in 1957 and Ekman in 1958 led Borg to develop a psychophysical category scale for ratings of perceived exertion (RPE).3. 4 This scale is a 15-point, graded scale with numbers ranging from 6 to 20. These numbers follow the normal heart rate (HR) range closely (60-200 beats per minute); in healthy middle-aged men, HR closely corre-sponds to 10 times the RPE value. Descriptive words are included with every other number and range from very, very light at 7 to very, very hard at 19 (Figure). Ratings of perceived exertion have been reported to show linear correlations with HR and work intensity with correlation coefficients between .80 and .90.3-5 High correlations with other physiological variables have also been found.6, 7 The Borg Scale has been proven valid and reliable in repeated tests of increasing work intensity with work loads either progressively or randomly ordered.3 In a single motor performance, high correlations have also been found between perceived exertion and pro-

duced force.8 At constant intensities and low work loads, low correlations from .20 to .50 between RPE and HR have been found.59

PHYSIOLOGICAL FACTORS AND PERCEIVED EXERTION

The development and widespread adoption of a perceptual rating scale has facilitated the enormous growth of research on the topic of perceived exertion in recent years. Numerous studies have attempted to identify the physiological factors that give rise to perception of exertion. These factors have been divided into those that produce either local or more generalized, central effects. Local signals include aches, cramps, pain, or fatigue that arise from feelings of strain in active muscles, tendons, and joints.7 The greater the feeling of strain in the exercising muscles, the more intense the local signals become.10 Lactate levels and oxygen debt associated with anaerobic work of the exercising muscle appear to be important factors in the generation of local signals.11,12 During heavy work, the energy available from aerobic processes is insufficient to meet the demands, producing an oxygen deficit and causing the muscle to rely on anaerobic processes to provide energy for contraction. During dynamic activities involving large muscle mass (eg, cycling), the anaerobic threshold may not be reached until 60 to 65 percent of

Response 6 7 8 9

10 11 12 13 14 15 16 17 18 19 20

Descriptors

Very, very light

Very light

Fairly light

Somewhat hard

Hard

Very hard

Very, very hard

Figure. The 15-point grade scale for ratings of perceived exertion, the RPE scale.2

Ms. O'Sullivan is Assistant Professor of Physical Therapy, Department of Physical Therapy, Sargent College of Allied Health Professions, Boston Uni-versity, Boston, MA 02215 (USA).

This article was submitted March 28, 1983; was with the author for revision 11 weeks; and was accepted October 24, 1983.

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maximal aerobic power (MAP).13 The anaerobic threshold during arm exercise, which uses a smaller muscle mass, is generally reached sooner.13, 14 A major end-product of anaer-obic metabolism is lactic acid. Thus, lactate concentration is a potent influence on perceived exertion. At high exercise intensities, its influence is significant, but at low intensities, its influence is minimal.15 The muscular discomfort of meta-bolic acidosis that results from high lactate levels is readily perceived as a conscious sensation by the exercising individ-ual.

Kinesthetic information arising from proprioceptive mech-anisms (mechanoreceptor, Golgi tendon organ activity, and sensations from muscle, ligament, joint, and skin) provides another important source of local cues. In studies comparing cycling with running, perceived exertion was found to be higher for cycling than for treadmill running at constant submaximal workloads.10 This higher level is not a surprising finding when one considers that cycling involves more intense work by fewer muscles than does running. At the same power output, pedalling at a lower frequency (40 rpm) caused per-ceived exertion to be higher than at higher frequencies (60 rpm). Increased muscle tension at the lower frequencies was again implicated in the more intense perceptual response.16. 17

Central factors reflect the circulatory, respiratory, and met-abolic adjustment to aerobic work. Signals such as HR, cate-cholamine levels, pulmonary ventilation (VE), respiratory rate (RR), overall feelings of exertional dyspnea, oxygen consump-tion (Vo2), and skin temperature all play a role in determining the magnitude of the central response to physical work.2. 6 Mihevic notes that the term "central" in perceived exertion literature takes on an entirely different meaning than that traditionally accepted in the physiological literature (ie, the central nervous system).15

The strong linear relationship between HR and perceived exertion was originally suggested by Borg and has been upheld in numerous studies in recent years.2 Correlation coefficients from .80 and .90 have been found between HR and RPE in a variety of work tasks (bike and treadmill and arm and leg work) and under varying exercise conditions (from moderate to heavy intensity, continuous or intermittent).2. 5. 6. 18

The RPE-HR relationship can be altered under certain conditions. When subjects are administered propranolol, a beta-adrenergic receptor blocking agent, the HR remains low while the RPE increases similarly to the results of control studies.10, 19 When environmental heat is introduced into the test environment, HR is significantly increased while the RPE remains proportional to the levels of work intensity.20-22 These and other studies in which HR was manipulated with either pharmacological or environmental conditions lend support to the concept that HR is not a major sensory cue for perceived exertion. Robertson suggests this strong linear re-lationship is probably the result of other hemodynamic factors such as cardiac output, stroke volume, or blood pressure.6 Studies on the effects of aging on perceived exertion reveal that the HR necessary to produce a given RPE score declined with age, roughly corresponding to the decline in maximal HR.18. 23

Ventilatory signals that are readily monitored by the exer-cising individual include sensations of breathlessness and dyspnea. Strong correlations exist between ventilatory func-tion, respiratory rate, and perceived exertion (.61-.94).6, 15 These relationships are particularly true at high exercise in-

tensities where peak exercise intensities have been found to coincide with peak ventilation.15 At low to moderate exercise intensities (below 50% MAP), these signals appear to have less of an impact as a cue for perceived exertion. When pulmonary ventilation was manipulated by breathing a hy-poxic gas mixture, RPE scores remained unaltered at low levels of exercise, but at high levels of exercise (70% MAP), both VE and RPE scores were significantly higher when com-pared with control scores.24 Hypnotic suggestion introduced changes in both perceptual and metabolic responses to exer-cise following the direction of the suggestion. Although actual workloads remained unchanged, VE and RPE scores closely corresponded to hypnotic suggestions of light, moderate, or heavy work.25 The results suggest that ventilation probably provides an important central sensory cue for perceived ex-ertion.

Perceived exertion has also been studied in relation to aerobic power. When RPE is correlated with Vo2, strong correlations ranging from .76 to .97 have been found.6. 26. 27 A number of studies have investigated the perceptual differences at absolute and relative levels of Vo2. Ratings of perceived exertion values were, on the average, 2 to 3 units higher for older subjects at absolute levels of Vo2, but no significant differences were found when oxygen uptake was expressed as a percentage of MAP.18 Similar effects were noted in studies on sex differences. At controlled intensities of work and Vo2, women experienced a higher rating of perceived exertion than men. When oxygen uptake was expressed as a percentage of MAP, however, scores were independent of sex.17 These stud-ies indicate that the relationship of perceived exertion to Vo2 consumption is closely related to the proportion of maximum working capacity required to perform a given work load relative to Vo2max and not to an absolute work load.

PSYCHOLOGICAL FACTORS AND PERCEIVED EXERTION

Morgan suggested that the unexplained variance between perception of exertion and physiological variables may be caused by the presence of psychological variables.25 He found that anxious, depressed, or neurotic individuals consistently interpret subjective sensations of physical work inaccurately and postulated that this may be the result of their altered states of autonomic arousal. Bartley suggested a similar model in which homeostatic and comfort systems serve as a base for understanding the perceptual systems.28 Morgan also found that extroverted individuals perceive the same work load as lighter than a group of introverted subjects.25 Robertson et al found that individuals who consistently augment or magnify the intensity of stimulation perceive the same work load as more intense than individuals who reduce or attenuate the intensity of their sensations.29 Because the physiological re-sponses of the groups were similar at a given work load, this study concluded that the contrasting styles of "stimulus inten-sity modulation appeared to have differentially influenced the perceptual responses to muscular exertion."29 These findings are supportive of Morgan's because individuals classified as extroverts and reducers are known to have a high pain toler-ance and more readily participate in athletics.30 Both Morgan25 and Robertson et al29 note that perceptual responses may be confounded by "state- versus trait-dependent" com-ponents. That is, individuals may characteristically function

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PRACTICE

in one way (trait-dependent), but under certain circumstances (eg, extreme stress) may change the way they characteristi-cally function, thereby becoming state-dependent. For ex-ample, trait augmenters may become reducers under ex-tremely fatiguing endurance exercise or under the influence of certain drugs, such as alcohol and aspirin. Highly anxious subjects may reduce their state of anxiety by performing strenuous physical exercise, but similar exercise may increase the state of low anxious subjects. Thus, psychological com-ponents of state and trait may influence a subject's perceived exertion and the interaction of the two may provide an additional source for interpreting inconsistent findings in the literature.

SENSORY INTEGRATION AND PERCEIVED EXERTION

Borg originally proposed that during a short bout of work, perceptions originated from the working muscles, whereas during a prolonged bout of work, central signals from the organs of circulation predominated.1. 2 This two-factor model was further elaborated by Ekbloom and Goldbarg.10 Their subjects were asked to rate separately local factors (muscle and joint feeling) and central factors (breathing and HR). Mihevic suggests that this is a simplistic approach to a com-plex psychobiological problem.15 Perception of exertion ap-pears to be a generalized response resulting from the sum-mation of many different sensations, each having a separate perceptual weighting (Table).31-34 Although signals that are more pronounced may dominate the sensory integration mechanism, all signals are received. The particular conditions of the exercise (such as type, mode, intensity, duration, and conscious processing of the signals involved) determine the perceptual responsiveness to work.6, 7, 15, 35 As the load becomes heavier, perceptual discrimination may increase.14 The exact mechanism by which these physiological and psychological signals are processed and integrated remains unclear. Al-though little research has been done to delineate the sensory integration mechanisms, researchers are now beginning to pursue this phase of investigation.

THERAPEUTIC IMPLICATIONS

Borg originally suggested that the most interesting applica-tion of perceived exertion ratings was in the area of exercise prescription.3 Target HRs and training levels might be accu-rately regulated in some individuals by subjective ratings of perceived exertion. Initial exercise training might be focused on helping individuals accurately adjust the intensity of work by feelings of how hard their body is working.

In a recent study of subjective regulation of work intensity during treadmill exercise, Smutok et al noted a progressive difference in HR at the same RPE between exercise stress testing and subjectively rated exercise.9 Ratings of perceived exertion were found to be reliable in determining conditioning HR above 9 km per hour. Ratings of perceived exertion values below these levels were inaccurate and unreliable in determin-ing conditioning HR. Thus, reliability of subjective exercise regulation seems to be related to the intensity of exercise. They also noted a large range of intraindividual HR error across all RPE values and suggested that some subjects are far more accurate in regulating exercise intensity by RPE than others. This variability may be more the result of the presence

of psychological factors than the result of physiological ones. Noble suggested that attempts to use "an estimation technique (Borg Scale) for a production problem (training control)" may be inappropriate.36 In a more recent study, Gutman et al had patients with cardiac disease work at a tolerable level (self-selected intensities) and found that training HRs and RPEs approximated those obtained during exercise stress testing.37 In an earlier study of patients with coronary heart disease, RPEs were found to be higher in relation to HR than those in a control group of healthy subjects working at similar work loads.21 Squires et al found that cardiac patients on propran-olol demonstrated a lower HR during submaximal and max-imal exercise when compared with those not receiving pro-pranolol, but RPE was the same for both groups at similar work loads.19 Patients with arterial hypertension and vasore-gulatory asthenia syndrome rated the perceived exertion as less in relation to HR, especially at low-intensity exercise levels. Because coronary patients have a relatively low, symp-tom-limited maximal HR, these findings are consistent with those of Smutok et al.9 At low HRs and low exercise intensi-ties, ratings of perceived exertion may not be a reliable indi-cator of HR. Patients who have angina pectoris do not appear to have a high correlation between perceptions of angina and perceptions of effort. As Noble reports, the angina scale developed by Borg, Holmgren, and Ludblad may be a more effective scale to monitor their responses.36

Therapeutic training regimens do not appear to alter the relationship between HR and RPE.38 When both HR and RPE are expressed as a percentage of MAP, differences are not observed. This similarity is understandable because Vo2max uptake or work capacity increases with training. The relationship between training and RPE and HR was not supported in a recent study of elderly subjects by Sidney and Shephard.18 After a 34-week training period, HRs declined, but ratings of perceived exertion remained unchanged or were augmented. One explanation for this unpredicted finding is that the habitual light mode of daily activity present before the study was perceived as being of above average intensity.

TABLE Subjective Symptoms of Prolonged Worka

Levels of Perceptual Processing

Low discom-fort/inten-sity (move-ment aware-ness)

Moderate discomfort/ intensity

High discom-fort/inten-sity

Local

muscle aches

muscle fa-tigue

legs aching, heavy

muscle pain, cramps

legs shaky, tremors

Subjective Symptoms

General

feeling tired perspiring

perspiring feelings of

pain/task aversion

Cardio-pulmonary

dyspnea breathlessness

difficulty with breathing

heart pound-ing/chest pain

a Modified from Robertson6 and Pandolf.32

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CONCLUSION

Ratings of perceived exertion appear to be a useful tool for quantifying some of the perceptions we experience during prolonged bouts of exercise. The RPE provides us with an estimate of the subjective costs of physical activity that may or may not be at variance with the actual physiological costs. In young and healthy middle-aged subjects who exercised at moderate to high intensities, RPE has been shown to be a direct measure of physiological stress as well as an indirect measure of physical work capacity. In elderly persons and certain patient groups with cardiovascular or psychiatric prob-lems and in certain environmental and drug situations, the relationship between HR and RPE appears to be altered.

Research on perceived exertion has been largely focused in the laboratory setting and needs to be applied more fully to the clinical setting to evaluate its usefulness. For individuals exercising at restricted HRs and in acute situations where accuracy may mean the difference between life and death, RPE is inappropriate to use alone as either an assessment or prescriptive tool in measuring work capacity. Borg notes the

"perfect indicator of dangerous strain" involves a number of important factors including HR, arrhythmias, ST segment changes, blood pressure elevations, and energy costs.4 When perceived exertion is used in conjunction with these indica-tors, it adds dimension to the assessment of response and regulation of exercise in certain patients. Heightened percep-tual awareness of the body's response to the stresses of pro-longed work can provide valuable information to patients, helping them to get "in tune" with and "listen" to their bodies. In clinical or physical fitness settings, this increased awareness may serve to prevent unnecessary strain or injury. Noble recommends studying the usefulness of perceived exertion as a predictor of physical fitness in school environments.36

Widespread use of the Borg scale has proven it to be a useful tool for many clinicians and patients. Its misuse must be guarded against, however, and the limitations of a psycho-physical rating scale must be clearly understood. Borg suggests that one perfect scale useful in all situations for perceptual rating may not exist.4 What is clearly evident in published research is an increased use of perceptual information as an indicator of physical strain.

REFERENCES

1. Borg G: Physical Performance and Perceived Exertion. Lund, Sweden, Gleerup, 1962, pp 10-11

2. Borg G: Perceived exertion. In Wilmore J (ed): Exercise and Sports Science Reviews. New York, NY, Academic Press Inc, 1974, vol 2, p 131

3. Borg G: Perceived exertion: A note on history & methods. Med Sci Sports 5:90-93, 1973

4. Borg G: Psychophysical bases of perceived exertion. Med Sci Sports Exerc 14:377-381,1982

5. Skinner J, Hutsler R, Bergstrinova V, et al: The validity and reliability of a rating scale of perceived exertion. Med Sci Sports, 5:94-96,1973

6. Robertson R: Central signals of perceived exertion during dynamic exer-cise. Med Sci Sports Exerc 14:382-389,1982

7. Cafarelli E: Peripheral contributions to the perception of effort. Med Sci Sports Exerc 14:382-389,1982

8. Cooper D, Grimby G, Jones D, et al: Perception of effort in isometric and dynamic muscular contraction. Eur J Applied Physiol 41:173-180,1979

9. Smutok M, Skrinar G, Pandolf K: Exercise intensity: Subjective regulation by perceived exertion. Arch Phys Med Rehabil 61:569-574,1980

10. Ekbloom B, Goldbarg A: The influence of training and other factors on the subjective rating of perceived exertion. Acta Physiol Scand 83:399-406, 1971

11. Kay C, Shephard R: On muscle strength and the threshold of anaerobic work. Int Z angew Physio 27:311-328,1969

12. Allen P, Pandolf K: Perceived exertion associated with breathing hyperoxic mixtures during submaximal work. Med Sci Sports 9:122-127,1977

13. strand P, Rodahl K: Textbook of Work Physiology. New York, NY, McGraw-Hill Inc, 1970, pp 279-318

14. Blitz P, VanMoorst A: Physical fatigue and the perception of differences in load: A signal detection approach. Percept Mot Skills 46:779-790,1978

15. Mihevic P: Sensory cues for perceived exertion: A review. Med Sci Sports Exerc 13:150-163,1981

16. Lollgen H, Graham T, Sjogaard G: Muscle metabolites, force and perceived exertion bicycling at varying pedal rates. Med Sci Sports Exerc 14:345-351,1980

17. Henrikson J, Knuttgen H, Binde-Peterson T: Perceived exertion during exercise with concentric and eccentric muscle contractions. Ergonomics 15:537-544,1972

18. Sidney K, Shephard R: Perception of exertion in the elderly, effects of aging, mode of exercise and physical training. Percept Mot Skills 44:999-1010,1977

19. Squires R, Rod J, Pollock M, et al: Effect of propranolol on perceived exertion soon after myocardial revascularization surgery. Med Sci Sports Exerc 14:276-280,1982

20. Pandolf K, Carfarelli E, Noble B, et al: Perceptual responses during prolonged work. Percept Mot Skills 35:975-985,1972

21. Skinner J, Hutsler R, Bergsteinova V, et al: Perception of effort during different types of exercise and under different environmental conditions. Med Sci Sports 5:104-109,1973

22. Noble B, Miltz K, Pandolf K, et al: Perceptual responses to exercise: A multiple regression study. Med Sci Sports 5:104-109,1973

23. Borg G, Linderholm H: Perceived exertion and pulse rate during graded exercise in various age groups. Acta Med Scand [Suppl] 472:194-206, 1967

24. Cafarelli E, Noble B: The effect of inspired carbon dioxide on subjective estimates of exertion during exercise. Ergonomics 19:581-589,1976

25. Morgan W: Psychological factors influencing perceived exertion. Med Sci Sports 5:97-103,1973

26. Noble B, Metz K, Pandolf K, et al: Perceived exertion during walking and running. Med Sci Sports 5:116-120,1973

27. Horstman D, Morgan W, Cymerman A, et al: Perception of effort during constant work to self-imposed exhaustion. Percept Mot Skills 48:1111-1126,1979

28. Bartley S: Homeostatic and comfort perceptual systems. J Psychol 75:157-162,1970

29. Robertson R, Gillespie R, Hiatt E, et al: Perceived exertion and stimulus intensity modulation. Percept Mot Skills 45:211-218,1977

30. Morgan W, Costill D: Psychological characteristics of the marathon runner. J Sports Med Phys Fitness 12:42-46,1972

31. Pandolf K, Buise R, Goldman R: Differentiated rating of perceived exertion during conditioning of older individuals using leg-weight loading. Percept Mot Skills 40:563-574,1975

32. Pandolf K: Differentiated ratings of perceived exertion during physical exercise. Med Sci Sports Exerc 14:397-405,1982

33. Gillespie R, McCarthy J, Rose K: Differentiated perceptions of exertion: Part 1, mode of integration of regional signals. Percept Mot Skills 49:683-689,1979

34. Gillespie R, McCarthy J, Rose K: Differentiated perception of exertion: Part 2, relationship to focal and central physiological responses. Percept Mot Skills 49:691-697,1979

35. Young A, Cymerman A, Pandolf K: Differentiated ratings of perceived exertion are influenced by high altitude exposure. Med Sci Sports Exerc 14:223-228,1982

36. Noble B: Clinical applications of perceived exertion. Med Sci Sports Exerc 14:406-411,1982

37. Gutman M, Squires R, Pollack M, et al: Perceived exertion-heart rate relationship during exercise testing and training in cardiac patients. Journal of Cardiac Rehabilitation 1:52-59,1981

38. Docktor R, Sharkey B: Note on some physiological and subjective reactions to exercise and training. Percept Mot Skills 32:233-234,1971

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