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:

  1. Borg, G. (1998). Borg’s perceived exertion and pain scales. Champaign, IL: Human Kinetics.
  2. 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.
  3. Eston, R. G. (2012). Use of ratings of perceived exertion in sports. International Journal of Sports Physiology and Performance, 7, 175–182.
  4. Eston, R. G., & Parfitt, C. G. (2007). Effort perception. In N. Armstrong, Paediatric exercise physiology (pp. 275–298). London: Elsevier.
  5. Morgan, W. P. (1994). Psychological components of effort sense. Medicine & Science in Sports and Exercise, 26, 1071–1077.
  6. Noble, B. J., & Robertson, R. J. (1996). Perceived exertion. Champaign, IL: Human Kinetics.
  7. 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.
  8. 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.

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