Effort

Individuals possess a remarkable ability to detect and interpret sensations arising from the body during physical work. As noted by William P. Morgan, terms such as perceived exertion, perception of effort, and effort sense have been used to describe this psychophysiological phenomenon. Interest in this aspect of performance was initiated by the pioneering work of the Swedish psychophysicist Gunnar Borg in the early 1960s. He introduced the concept of perceived exertion and proposed ways by which overall exertion, breathlessness, and localized sensations of fatigue could be numerically and verbally rated. This led to the development of rating of perceived exertion (RPE) scales, the most common of which is the Borg 6–20 RPE Scale. This entry describes Borg’s concept of perceived exertion and outlines its underpinning factors, methods of measurement, and how it has been used.

Effort Continua

Borg originally proposed that subjective responses to an exercise stimulus involve three main effort continua: perceptual, physiological and performance. Although a number of more complex models of perceived exertion have been developed, they are founded on the same three effort continua. Borg used the perceptual continuum as the initial basis from which to explore the derivations of the ratings of perceived exertion, on the premise that perception plays a fundamental role in human behavior and in how one adapts to a situation. He stressed that the perceptual continuum will be influenced by a person’s subjective experience and that these experiences will be directly affected by psychological traits. The physiological continuum includes a wide variety of variables, such as heart rate, blood lactate, oxygen uptake, and ventilation, which may be characterized by different growth curves as a function of exercise intensity. For example, heart rate and oxygen uptake are characterized by a linear growth in relation to increases in intensity as measured by power output (watts), whereas blood lactate concentration and ventilatory volume are characterized by a nonlinear (positively accelerating) growth function.

The influence of the perceptual and physiological continua on RPE will also be moderated by the situational characteristics of the performance (the third continuum). In this regard, one has to take into account the nature of the performance and the social and physical environment in which it takes place. Performance may involve timed (short or long) incremental stages to exhaustion, the highest workload that can be sustained for a specific period of time, the greatest distance one can cover in a given time period or the fastest time in which one can cover a given distance. Submaximal performances may involve monitoring the time to exhaustion at a given exercise intensity (for example, at a given percentage of maximal oxygen uptake or at an intensity corresponding to a ventilatory threshold reference point). Knowledge of the duration of the task or distance to be completed is also a critical factor in gauging effort. Social environmental factors may include whether or not performance is alone or with others, whether it is competitive, the presence or absence of an audience, and how supportive the audience is. Physical environmental factors include location, ambient conditions of temperature, humidity, and altitude, and any external distractions such as music and visual stimuli.

So, effort perception involves the collective integration of afferent feedback from cardiorespiratory, metabolic and thermal stimuli and feed forward mechanisms to enable an individual to evaluate how hard or easy an exercise task feels at any point in time. It is moderated by psychological factors, such as personality traits, cognition, memory, previous experience and understanding of the task; situational factors, such as knowledge of the end-point, duration, and temporal characteristics of the task; and social and physical environmental factors. The extent to which these factors moderate the perception of exertion has been shown to be exercise intensity dependent.

Measurement and Calibration of Effort

The most common method of measuring perceived exertion is the Borg 6–20 Category Scale followed by the Borg Category Ratio 10 (CR10) Scale. The development and correct use of these scales is described in detail by Borg. The scales are designed to assess sensations of exertion in relation to physiological markers, such as heart rate and oxygen uptake, which rise commensurately with increments in exercise intensity. In both scales, numbers are anchored to verbal expressions. For example, in the 6–20 Scale the numbers 6, 9, 11, 13, 15,

17, 19 and 20 are anchored to verbal expressions of “no exertion at all, very light, light, somewhat hard, hard, very hard, extremely hard and maximal exertion,” respectively. As research questions and applications involving perceptions of exertion have developed, a number of additional scales for adults have been developed. These include Foster’s 0–10 Session RPE Scale, used in the calculation of an athlete’s training load, and Garcin’s 1–20 Estimated Time Limit Scale, which is used in the estimation of the time remaining until volitional exhaustion.

As the antecedents of RPE include the memory of physical work experiences and the level of cognition and understanding, a number of simplified RPE scales for children have also been developed. For a child to perceive effort accurately, and then reliably produce a given intensity at a given RPE, learning must occur. Implicit in the process of learning is practice and the cognitive ability of the child. According to Jean Piaget’s stages of development, children around the ages of 7 to 10 years can understand categorisation but find it easier to understand and interpret pictures and symbols rather than words and numbers. For this reason, more recent pediatric RPE scales include pictures to portray the degree of effort and acute fatigue experienced and understood by the child. These developments have also recognized the need for verbal descriptors and terminology that are more pertinent to a child’s cognitive development, age, and reading ability. These scales therefore use a limited number range based around 0 to 10 or 1 to 10, pictorial descriptors, and wording that is more familiar to children (e.g., Roger Eston and colleagues’ CERT, BABE, CALER, E-P Scales and Robertson’s OMNI Scales).

Central and Localized RPE

Sensations of effort can be used to assess overall respiratory–metabolic (central) perceptions of exertion or they can be used to differentiate between central and peripheral (local) signals of exertion. For example, differentiated ratings of perceived exertion may be used to segregate the sensations arising from the upper body and the lower body during cycling exercise or during rowing, running, or stepping. For cycling, localized perception of exertion in the leg muscles tends to dominate the overall perceived exertion response. Consequently, the strength of the perceptual signal of exertion is greater for a given work rate for cycling compared to treadmill exercise.

Estimation and Production of Effort

The sensation of effort has been applied in a variety of ways to assess and understand performance. It is generally observed that RPE measured during an exercise bout increases as exercise intensity increases in adults and children, particularly when the exercise stimulus is presented in an incremental fashion. Such relationships have been most frequently observed using the so-called passive estimation paradigm. In this way, a rating of perceived exertion is given in response to a request from the exercise scientist or clinician to indicate how “hard” the exercise feels. The information can be used to assess changes in fitness using standardized submaximal exercise test procedures, such as in the Lamberts and Lambert Submaximal Cycling Test. It may also be used to assist the clinician or coach in prescribing exercise intensities. For example, an exercise intensity (e.g., heart rate, work rate or oxygen uptake), which coincides with a given RPE, may be prescribed by the coach or clinician.

Given the robust relationship between RPE and exercise intensity, particularly if known for an individual, the RPE can be used as a subjective guide to gauge exercise intensity during cardiorespiratory and resistance exercise. Thus, an active production paradigm can be employed whereby the individual is requested to regulate exercise intensity to match specified RPE values. A number of studies show support for the use of the RPE in this way for both aerobic fitness training and for estimating aerobic power and fitness.

Assessment of Training Load

As optimization of training load is a key factor for peak performance, the quantification of effort is considered to be important. Recently, the session RPE method, calculated by multiplying the relative perceived exertion of the session (scale of 0–10) by the duration of the exercise (in minutes), or the number of repetitions for resistance training, has become a popular method of assessing acute and chronic training load in athletes.

Prediction of Maximal Exercise Levels

The RPE elicited from submaximal work rates can be used to provide acceptable predictions of maximal aerobic power (VO2max) that are as good as or better than heart rate. This is true for healthy active and sedentary groups and able-bodied and paraplegic athletes. The RPE also predicts 1-RM (one repetition maximum) in adults and children and maximal intermittent vertical jump performance.

It has been noted that RPE 20 is infrequently reported at volitional exhaustion during maximal incremental exercise tests or constant-load tests to maximal volitional exhaustion. As the subjective limit of fatigue normally occurs around RPE 19 (extremely hard) on the Borg 6–20 scale, studies have shown that RPE 19 is a better predictor of VO2max than the theoretical maximal RPE 20.

Perceptually Regulated Exercise Testing

On the basis that RPE alone may be used to regulate exercise intensity, perceptually regulated exercise testing is an alternative method of estimating maximal exercise capacity and training status. The standard procedure involves a series of short incremental stages (2, 3 or 4 min.) that are clamped to RPEs of 9, 11, 13, 15 (and sometimes 17). Extrapolation of the individual RPE: intensity relationship to a maximal RPE (19 or 20) enables VO2max or maximal work rate to be estimated with reasonable accuracy. This method has the advantage of allowing subjects the autonomy to set the intensity of exercise to a given RPE, through changes in pace, work rate, or gradient. First applied in cardiac patients, the efficacy of this method has been confirmed across a broad range of ages, fitness levels, and levels of physical ability.

Relationship With Time or Distance Remaining to Exhaustion

When the RPE is expressed against the proportion (%) of the time or distance completed, regardless of the length of an effort, the RPE rises similarly relative to the percentage of distance or duration completed or yet to be completed. This has been observed in open-loop, fixed intensity exercise to exhaustion (in which the distance or time is unknown) and during closed-loop tasks (the duration or distance to the end point is known) despite the effects of changed environmental conditions and competitive distances. Certainty about the exact duration and end point has been shown to affect both the RPE strategy and performance, as the rate of increase in perceived exertion is not always constant in all conditions, but changes in relation to the degree of certainty about the endpoint of exercise as well as exercise duration. Disruption in the rate of RPE increase occurs when uncertainty about the anticipated end point is invoked by deception during fixed intensity cycling and treadmill exercise.

The practical implication of this knowledge is that it is theoretically possible to use the rate of increase in the RPE to estimate the exercise duration or time remaining to exhaustion at a given work rate or pace. It is postulated that athletes continually compare their momentary or conscious RPE with an expected RPE (the “template RPE”) through a process of internal negotiation at a particular portion of a race, and adjust pace to match the anticipated and experienced values for RPE Murielle Garcin and colleagues introduced the 1–20 Estimate Time Limit (ETL) scale to provide a direct measure of how the effort at any given point during exercise can be used to provide a subjective estimation of the time remaining to exhaustion. The validity and applications of the scale have been reviewed by Coquart et al. (2012). In this scale, the numbers 17, 13, 9 and 4 relate to an anticipated end time to exhaustion of 4, 15 and 60 minutes and 2 hours, as listed on the ETL Scale, respectively. The ETL scale provides further information on the psychological load (intensity and duration) of exercise and allows for a direct subjective estimation of time that can be maintained at any intensity and at any given instant. Use of the ETL, in conjunction with the RPE, provides a further method of understanding the relationship between perceived effort, exercise intensity, and the duration that remains until physical exhaustion.

Conclusion

The concept of perceived exertion is a key variable of interest in sport and exercise science. It has applications in children and adults, from sedentary through elite athletic status. Practitioners have used it successfully with paraplegic, partially sighted, obese, cardiac and other clinical populations. It can be used to predict the limits of exercise, to regulate exercise intensity, to assess training load and to compare training status. However, its utility has to be considered within the dynamic context of the fundamental continua originally identified by Borg.

References:

Borg, G. (1998). Borg’s perceived exertion and pain scales. Champaign, IL: Human Kinetics.
Coquart, J. B., Eston, R. G., Noakes, T. D., TournyChollet, C., L’hermette, M., Lemaitre, F., et al. (2012). Estimated time limit: A brief review of a perceptually based scale. Sports Medicine, 42, 845–855.
Eston, R. G. (2012). Use of ratings of perceived exertion in sports. International Journal of Sports Physiology and Performance, 7, 175–182.
Eston, R. G., & Parfitt, C. G. (2007). Effort perception. In N. Armstrong, Paediatric exercise physiology (pp. 275–298). London: Elsevier.
Morgan, W. P. (1994). Psychological components of effort sense. Medicine & Science in Sports and Exercise, 26, 1071–1077.
Noble, B. J., & Robertson, R. J. (1996). Perceived exertion. Champaign, IL: Human Kinetics.
Scherr, J., Wolfarth, B., Christle, J. W., Pressler, A., Wagenpfeil, S., & Halle, M. (2012). Associations between Borg’s rating of perceived exertion and physiological measures of exercise intensity. European Journal of Applied Physiology, 113, 147–155.
Tenenbaum, G., & Hutchinson, J. C. (2007). A socialcognitive perspective of perceived and sustained effort. In G. Tenenbaum & R. C. Eklund (Eds.), Handbook of sport psychology (3rd ed., pp. 560–577). Hoboken, NJ: Wiley.