I was reading these two very short articles:
Sense of effort and other unpleasant sensations during exercise: clarifying concepts and mechanisms. Smirmaul BD.
The sense of effort is an essential component of all forms of exercise. Although extensively studied, exercise physiologists have failed to reach consensus about whether this sensation is based on afferent sensory feedback or is centrally generated and independent of such feedback. This confusion has led to misunderstandings regarding the neurological mechanisms responsible for the sense of effort as opposed to other specific sensations such as pain and temperature.
A mechanism in which the sense of effort is centrally generated and independent of feedback had been proposed more than 150 years ago. However, a more recent concept of sense of effort as a subjective rating of exercise intensity based on various sensations experienced during exercise given by Borg may have caused confusion, especially among exercise physiologists. Many began to use and understand the sense of effort as a sensation that is generated by afferent sensory feedback. The information reviewed in this article, together with the examples given, constitutes a body of evidence in favour of a centrally generated sense of effort. Afferent sensory feedback is important for the conscious awareness of different sensations such as pain and temperature, and plays important roles in the control of homeostasis. However, peripheral sensory feedback does not seem to be important for the generation of the sense of effort.
The sense of effort and other specific sensations such as temperature, pain and other muscular sensations present two separate neurological mechanisms. While the former is centrally generated, the latter is based on afferent sensory feedback. An interaction of these sensations is likely the ultimate regulator of exercise performance. However, further investigation is required to fully understand these phenomena.
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:
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.
firstname.lastname@example.org Comment in:* Eur J Appl Physiol. 2010 Aug;109(6):1225-6.
In exercise physiology, it has been traditionally assumed that high-intensity aerobic exercise stops at the point commonly called exhaustion because fatigued subjects are no longer able to generate the power output required by the task despite their maximal voluntary effort. We tested the validity of this assumption by measuring maximal voluntary cycling power before (mean +/- SD, 1,075 +/- 214 W) and immediately after (731 +/- 206 W) (P < 0.001) exhaustive cycling exercise at 242 +/- 24 W (80% of peak aerobic power measured during a preliminary incremental exercise test) in ten fit male human subjects. Perceived exertion during exhaustive cycling exercise was strongly correlated (r = -0.82, P = 0.003) with time to exhaustion (10.5 +/- 2.1 min). These results challenge the long-standing assumption that muscle fatigue causes exhaustion during high-intensity aerobic exercise, and suggest that exercise tolerance in highly motivated subjects is ultimately limited by perception of effort.
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. email@example.com
Mental fatigue is a psychobiological state caused by prolonged periods of demanding cognitive activity. Although the impact of mental fatigue on cognitive and skilled performance is well known, its effect on physical performance has not been thoroughly investigated. In this randomized crossover study, 16 subjects cycled to exhaustion at 80% of their peak power output after 90 min of a demanding cognitive task (mental fatigue) or 90 min of watching emotionally neutral documentaries (control). After experimental treatment, a mood questionnaire revealed a state of mental fatigue (P = 0.005) that significantly reduced time to exhaustion (640 +/- 316 s) compared with the control condition (754 +/- 339 s) (P = 0.003). This negative effect was not mediated by cardiorespiratory and musculoenergetic factors as physiological responses to intense exercise remained largely unaffected. Self-reported success and intrinsic motivation related to the physical task were also unaffected by prior cognitive activity. However, mentally fatigued subjects rated perception of effort during exercise to be significantly higher compared with the control condition (P = 0.007). As ratings of perceived exertion increased similarly over time in both conditions (P < 0.001), mentally fatigued subjects reached their maximal level of perceived exertion and disengaged from the physical task earlier than in the control condition. In conclusion, our study provides experimental evidence that mental fatigue limits exercise tolerance in humans through higher perception of effort rather than cardiorespiratory and musculoenergetic mechanisms. Future research in this area should investigate the common neurocognitive resources shared by physical and mental activity.
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:
Exercise and fatigue.Ament W, Verkerke GJ.Department of Biometrics, Faculty of Health and Technology, Zuyd University, Heerlen, the Netherlands. firstname.lastname@example.org
Physical exercise affects the equilibrium of the internal environment. During exercise the contracting muscles generate force or power and heat. So physical exercise is in fact a form of mechanical energy. This generated energy will deplete the energy stocks within the body. During exercise, metabolites and heat are generated, which affect the steady state of the internal environment. Depending on the form of exercise, sooner or later sensations of fatigue and exhaustion will occur. The physiological role of these sensations is protection of the exercising subject from the deleterious effects of exercise. Because of these sensations the subject will adapt his or her exercise strategy. The relationship between physical exercise and fatigue has been the scope of interest of many researchers for more than a century and is very complex. The exercise intensity, exercise endurance time and type of exercise are all variables that cause different effects within the body systems, which in turn create different types of sensation within the subject’s mind during the exercise. Physical exercise affects the biochemical equilibrium within the exercising muscle cells. Among others, inorganic phosphate, protons, lactate and free Mg2+ accumulate within these cells. They directly affect the mechanical machinery of the muscle cell. Furthermore, they negatively affect the different muscle cell organelles that are involved in the transmission of neuronal signals. The muscle metabolites produced and the generated heat of muscle contraction are released into the internal environment, putting stress on its steady state. The tremendous increase in muscle metabolism compared with rest conditions induces an immense increase in muscle blood supply, causing an increase in the blood circulatory system and gas exchange. Nutrients have to be supplied to the exercising muscle, emptying the energy stocks elsewhere in body. Furthermore, the contracting muscle fibres release cytokines, which in their turn create many effects in other organs, including the brain. All these different mechanisms sooner or later create sensations of fatigue and exhaustion in the mind of the exercising subject. The final effect is a reduction or complete cessation of the exercise. Many diseases speed up the depletion of the energy stocks within the body. So diseases amplify the effect of energy stock depletion that accompanies exercise. In addition, many diseases produce a change of mind-set before exercise. These changes of mind-set can create sensations of fatigue and exercise-avoiding behaviour at the onset of an exercise. One might consider these sensations during disease as a feed-forward mechanism to protect the subject from an excessive depletion of their energy stocks, to enhance the survival of the individual during disease.
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.
Thepacing strategy may be defined as the process in which the total energy expenditure during exercise is regulated on a moment-to-moment basis in order to ensure that the exercise bout can be completed in a minimum time and without a catastrophic biological failure. Experienced athletes develop a stable template of the power outputs they are able to sustain for different durations of exercise, but it is not known how they originally develop this template or how that template changes with training and experience. While it is understood that the athlete’s physiological state makes an important contribution to this process, there has been much less interest in the contribution that the athlete’s emotional status makes. The aim of this review is to evaluate the literature of physiological, neurophysiological and perceptual responses during exercise in order to propose a complex model interpretation of this process which may be a critical factor determining success in middle- and long-duration sporting competitions. We describe unconscious/physiological and conscious/emotional mechanisms of control, the focus of which are to ensure that exercise terminates before catastrophic failure occurs in any bodily system. We suggest that training sessions teach the athlete to select optimal pacing strategies by associating a level of emotion with the ability to maintain that pace for exercise of different durations. That pacing strategy is then adopted in future events. Finally, we propose novel perspectives to maximise performance and to avoid overtraining by paying attention also to the emotional state in training process.
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.