Ratings of Perceived Exhaustion vs Ratings of Perceived Effort
I was reading these two very short articles:
|Br J Sports Med. 2010 Jun 27. [Epub ahead of print]
Sense of effort and other unpleasant sensations during exercise: clarifying concepts and mechanisms. Smirmaul BD.
|Perception of effort during exercise is independent of afferent feedback from skeletal muscles, heart, and lungs »
Since I spent some time researching this RPE stuff, and have written an article that should be soon published on soccerspecific.com site, I came to conclusion:There is a difference between effort and exhaustion and the perception of it. The sense of effort is a centrally produced sensation (corollary discharge of motor pathway in brain) and it has nothing to do with afferent feedback. It is basically a sense of motor output (motor recruitment and discharge frequency): force output or power output.
The sense of exhaustion (sensation of unpleasantness) is a different part of the story, and I guess it is related to sense of effort and afferent feedback, basically providing the feedback about the “endangerment” of homeostasis (internal environment) perturbations.
To provide a real world distinction, here is a quote from the article by Smirmaul:
|Although probably presenting similar responses during common exercises such as continuous running or cycling, it is possible to notice that the sense of effort and other unpleasant sensations are clearly disassociated in various situations. A short maximal voluntary contraction for leg extension, for example, will by nature induce a maximal sense of effort while, initially, other unpleasant sensations will probably be modest. Repeating this maximal contraction several times, however, will increase these unpleasant sensations continuously, whereas the sense of effort will be always the same (ie, maximal). Another example is a marathon runner who, after contending head-to-head with an opponent, finishes the race. In the last metres, his/her sense of effort and other unpleasant sensations would be near to maximal. Just after finishing the marathon, however, despite still feeling many unpleasant sensations, his/her sense of effort would be dramatically reduced, while the only current effort expended would be to maintain the upright posture and the breathing. A last example is a cyclist who, after an uphill section, suddenly starts a downhill section and stops pedalling, going down solely with his own momentum. Although still feeling highly unpleasant sensations due to the uphill climbing, the effort expended to go down the downhill is virtually zero, which means a very low sense of effort.
The decision to measure either the sense of effort or other specific sensations during studies may vary according to the particular research aims. The instructions provided by the researchers to the subjects are crucial in order to determine which of these outcomes will be measured, as also highlighted by Marcora.9
Most of the athletes can differ between the two sensations. For example, providing submaximal isometric contraction till exhaustion (i.e. 200N for 2mins) will yield submaximal sense of effort (force produced) and different sense of exhaustion at different time dots during the contraction (zero at the begging, yet 100% at the point of exhaustion). It is hard to differ between the two at the point of exhaustion, but some athletes can do it.
The problem is that in the research lab coats doesn’t differ between the two, and use effort and exhaustion interchangeably. Even the questions asked to the athlete to assess this subjective feeling can yield different answers.There are some really good research at what actually cause exhaustion, and to make it short, it is not the failure at the periphery. it is the conscious decision to stop it. Here are some nice research to take a look by Marcora:
|Eur J Appl Physiol. 2010 Jul;109(4):763-70. Epub 2010 Mar 11.
The limit to exercise tolerance in humans: mind over muscle? Marcora SM, Staiano W.School of Sport, Health and Exercise Sciences, Bangor University, Normal Site, Holyhead Road, Bangor, Gwynedd LL57 2PZ, Wales, UK.
email@example.com Comment in:* Eur J Appl Physiol. 2010 Aug;109(6):1225-6.
|J Appl Physiol. 2009 Mar;106(3):857-64. Epub 2009 Jan 8.
Mental fatigue impairs physical performance in humans. Marcora SM, Staiano W, Manning V.School of Sport, Health and Exercise Sciences, Bangor University, Bangor, Wales, United Kingdom. firstname.lastname@example.org
|Eur J Appl Physiol. 2008 Nov;104(5):929-31; author reply 933-5. Epub 2008 Jul 10.
Do we really need a central governor to explain brain regulation of exercise performance? Marcora SM.
Basically, there is a labcoat fight between Noakes’ Central Governor and Marcora’s psycholobiological model based on motivational intensity theory. IMHO, both models can be correct since fatigue is task dependent and both provides interesting insights.Another interesting read:
|Sports Med. 2009;39(5):389-422. doi: 10.2165/00007256-200939050-00005.
Exercise and fatigue.Ament W, Verkerke GJ.Department of Biometrics, Faculty of Health and Technology, Zuyd University, Heerlen, the Netherlands. email@example.com
|Br J Sports Med. 2010 Jun 17. [Epub ahead of print]
The role of emotions on pacing strategies and performance in middle and long duration sport events.Baron B, Moullan F, Deruelle F, Noakes TD.Centre Universitaire de Recherches en Activités Physiques et Sportives, Département STAPS, Faculté des Sciences de l’Homme et de l’Environnement, Université de La Réunion, Le Tampon, France.
Anyway, both models by Marcora and Noakes provides usable additions for traditional exercise physiology (the role of emotions, knowledge of end point, RPE, etc). IMHO, both models are correct in a specific way – both explain regulation of the exercise by the CNS instead of the periphery (although again, in certain tasks/contexts failure at the periphery is the source of the exhaustion), but in different ways. Marcora’s psycholobiological model based on motivational intensity theory IMHO provides insight how the conscious (volition, motivation) part of the CNS affect performance (emotions, tolerable level of sustaining unpleasant feelings, etc).Noakes’ Central Governor IMHO opinion explains subconscious regulation of the performance.
For example, in tests to exhaustion couple of things can happen:
1. Even if the athlete tries to push as hard as possible, fatigue at the periphery (inside the muscle) may decrease the force output (motivation high, motor output high, periphery fatigued). I.e. Wingate bicycle test
2. Even if athlete tries to push as hard as possible even under really high RPE (sense of unpleasantness), CNS protective regulations due heat accumulation may reduce motor output even and reduce performance (power output) even if the fatigue at the periphery is not so high. Same thing can happen if the internal environment is endangered (pH, dehydration, heat, blood sugar, etc). (motivation high, motor output reduced, periphery normal) I.E. Prolonged exercise in the heat
3. During certain task athlete may stop the exercise due not willingness to sustain certain level of discomfort, aka disengagement, without reduced motor output, or too much fatigue at the periphery (motivation high, motor output reduced, periphery normal). I.E. cycle to exhaustion at 80% of [power]VO2max.
The take home message is that fatigue is task dependent and numerous factors may limit performance and exhaustion. IMHO, we need to differ between:
1) Peripheral factors of fatigue (changes in the muscle cell)
2) Central-Subconscious factors of fatigue aimed at maintaining internal environment (homeostasis)
3) Central-Conscious factors, or motivational-volitional-emotional factors. All three are interlaced, making the simple and reductionist statements (this factor cause fatigue, exhaustion) cannot explain this complex phenomena.