22 SAJSM  vol 24  No. 1  2012

EDITOR’S CHOICE

THE HISTORY AND MEANING OF FATIGUE
It is immensely difficult to provide a detailed historical account of the 
development of fatigue as a concept in the exercise sciences. However, 
the study of fatigue stretches back centuries to scientists such as 
Galvani, who provided the ideas and tools to undertake experiments 
related to the electrical impulses needed to animate skeletal muscles.1 
The definitive work of Mosso in the 18th Century stands as a 
landmark in the study of fatigue.2 In his book La fatica (fatigue),2 he 
concluded that there were two phenomena which categorised fatigue: 
“The first is the diminution of the muscular force. The second is 
fatigue as a sensation. That is to say, we have a physical fact which 
can be measured and compared, and a psychic fact which eludes 
measurement” (p 154). Notably, early textbooks such as Physiology of 
muscular exercise by Bainbridge in 19313 pointed out that the limit of 
exercise “has often been ascribed to the capacity of the heart alone, but 
the facts as a whole indicate that the sum of the changes taking place 
throughout the body brings about the final cessation of effort” (p 176). 
It is an interesting fact that research into fatigue is highly complex, and 
consensus about the aetiology of this human condition still evades us. 
Not surprisingly, even after centuries of research in this area, fatigue is 

still very much a part of medical and social discourse. There may be 
several reasons for this, not least of which could be the loss or change 
in the meaning of the term fatigue. The Oxford Dictionary4 defines 
fatigue as “extreme tiredness after exertion; reduction in efficiency of 
a muscle, organ etc. after prolonged activity”. Compare this definition 
to that of exhaustion which is often used interchangeably by exercise 
physiologists and which is defined as “a total loss of strength; to 
consume or use up the whole of ”.4 Clearly, these are substantially 
different meanings. In addition to these general meanings, there is 
wide variation in definitions of fatigue in the exercise sciences which 
include statements such as “the failure to maintain the required or 
expected force,”5 or “a loss of maximal force generating capacity”6 or 
“a reversible state of force depression, including a lower rate of rise of 
force and a slower relaxation”.7 There are many more statements or 
definitions like these which attempt to capture the specific observation 
that there has been a decline in the ability to produce skeletal muscle 
tension of a given magnitude in order to quantify the amount of 
fatigue that has developed.

Recently, it has been argued that meaning itself, the subjective sense 
a person attributes to an event or experience, tends to be overlooked in 
scientific research. As a result, we are left with a naïve understanding 
about the underlying mechanisms so that the subjective experience is 
nothing more than a series of brain states.8 The study of fatigue is an 
example of how scientific rules which ordinarily have finite meanings 
have constrained the pursuit of understanding the fatigue experience.

CENTRAL OR PERIPHERAL FATIGUE?
Much of what is reported in the literature about the mechanisms 
of fatigue is related to the reductionist and sometimes mutually 
exclusive dichotomy of either peripheral or central mechanisms with 
conclusions usually drawn about the contribution of each to the total 
outcome. One might argue that such a dichotomous paradigm is 
appropriate since it provides insights about the processes at specific 
sites. From these site-specific changes, one can apparently conclude 
whether the site of fatigue is located in the central nervous system 
or peripherally at or below the neuromuscular junction. However, 
over a century ago, Mosso wrote that “It is not will, not the nerves, 
but it is the muscle that finds itself worn out after the intense work 
of the brain”.2 Mosso expressly noted that the “fatigue of brain 
reduces the strength of the muscles”. This is perhaps one of the initial 
statements in this area of work which gave rise to the central versus 
peripheral paradigm and it may be this “either/or” approach that 
limits our investigations and understanding of fatigue. Moreover, this 
dichotomy excludes the obvious individual subjective assessment of 
fatigue. For example, during high intensity exercise of short duration, 
the fatigue that develops is thought to be primarily peripheral in 
origin so that the ability of the muscle to generate further tension is 
reduced because of changes to the properties of the surface membrane 

•This article was reproduced with permission from the BMJ Group. It was originally published in the 
British Journal of Sports Medicine 2011;45:65-67 (originally published online 2 December 2009).

The limits to exercise performance and the future of fatigue 
research*
F E Marino, M Gard, E J Drinkwater

School of Human Movement Studies, Charles Sturt University, Bathurst, New South Wales, Australia

Correspondence to: Professor Frank E Marino (fmarino@csu.edu.au)

ABSTRACT
The study of human fatigue stretches back centuries and remains 
a significant part of medical and social discourse. In the exercise 
sciences fatigue is routinely related to the ability to produce muscle 
force or to the recovery from force decrements. However, the study 
of fatigue has by virtue of the experimental paradigm excluded the 
subjective sense a person attributes to an event or experience, thus 
reducing our overall understanding of the fatigue process. Modern 
studies report the causes of fatigue as either central or peripheral 
in origin. Although useful, this dichotomy can also exclude 
the individual subjective assessment. Furthermore, adhering 
dogmatically to set parameters is likely limiting the advancement 
of our understanding. A more realistic paradigm would permit 
the individual to use the sensory cues to adjust the effort along 
with the fatigue process rather than rely purely on feedback 
mechanisms. Therefore, bringing feedforward mechanisms of the 
brain into fatigue research perhaps represents the next phase in the 
unravelling of the fatigue process.



SAJSM  vol 24  No. 1  2012 23

of the muscle fibre, the process of calcium release or the function 
of excitation–contraction coupling9 (pp 105-119). However, if the 
familiar feelings or sensations of “burning” that develop during this 
process have no meaning for the individual and play no role, then 
this removes completely the possibility that the individual is not 
adjusting their effort either consciously or subconsciously during the 
exercise. It seems intuitive that individuals would have some say over 
the way in which they deal with the fatigue that develops during this 
short intense exercise bout. However, the evidence for this is lacking 
probably because the protocols used to study fatigue do not allow 
for the individual to adjust their response relative to the feedback 
which might be available during exercise. It is because most of these 
tests are externally driven by an experimenter dictating the pace by, 
for example, a motorised treadmill that these tests are referred to as 
“brainless”.10

DEFINITIONS AND MODELS OF FATIGUE
There is an attraction to reaching a succinct and widely accepted 
definition of fatigue. Such a definition would be convenient for 
scientific investigation by providing a metric upon which to compare 
results. To base much of the sports and exercise science research on 
firmer footing could also add credibility to the discipline among 
the other natural sciences that have much more standardised 
metrics and terms of reference. However, to prematurely arrive at 
a definition that is only accepted because no better one exists may 
only confirm our own biases and misrepresent the reality of fatigue. 
For example, concise and intuitive theory has led us to routinely, but 
erroneously, explain fatigue with “lactic acid” for many decades.11 As 
a consequence, decades of research estimating metabolic acidosis and 
buffering on “lactic acid” is based on flawed theory. Considering our 
innate desire to understand a phenomenon, explaining fatigue with 
“lactic acidosis” persists12 even though there is now a gaping hole in 
our understanding of metabolic acidosis.

Similarly, that fatigue is based on feedback mechanisms has 
existed since Hill’s so-called “Catastrophe Model” of fatigue.13 The 
interpretations of VO2max testing made by Hill have guided how we 
quantify, understand and explain fatigue. That a model is concise or 
intuitive does not mean that we should cease looking to develop a 
better one, particularly when weaknesses in the Catastrophe Model 
come to light.14 While the “Central Governor Theory”15 might not be 
the final explanation of fatigue,16 a feedforward mechanism presents 
what is potentially the next step in advancing our understanding of 
fatigue. Considering that Hill’s classical theory has undergone very 
little modification since its inception in the 1920s, is it possible 
that the constraints of this theory are contributing to limiting our 
understanding of fatigue? 

A feedforward mechanism for explaining fatigue attempts to 
encompass events in which fatigue exists without exhaustion. The term 
“exhaustion” here does not necessary imply complete physical collapse 
but simply the inability to maintain the prescribed task (ie, task failure).17 
Our current understanding of fatigue based on Hill’s model cannot help 
us understand fatigue that involves voluntarily paced events like cycling 
time trials18 or team sports19 nor the fatigue associated with disease 
states.20 While most sporting events terminate with the occurrence of 
an event that is externally controlled (eg, the end of the race, expiry 
of the game clock), laboratory research investigating fatigue usually 
begins with no known end target and ends with voluntary termination. 
Athletes must consciously self-pace themselves to time the end of the 
event with fatigue while maintaining optimal performance.21 22 By 

removing conscious control over pacing, tests like the VO2max are not 
specific to the phenomenon of self-paced events.13 Applying research 
results from externally paced tests to help us understand fatigue during 
self-paced events is entirely inappropriate. 

It is possible that a multitude of explanations for fatigue exist, 
ranging from metabolic disturbances in the motor unit to mechanisms 
that are centrally mediated.23 The balance of central and peripheral 
mechanisms may be partially dependent upon duration/intensity of 
fatigue and the muscle group being assessed.24 However, that they are 
all based on feedback mechanisms seems to be a limiting factor in how 
we explain fatigue, particularly when considering the feedforward 
mechanisms necessary for the anticipation of fatigue and pacing 
strategies for self-paced events. While the nature of modern research 
often requires progressively greater specialization and refinement of 
theories, opportunities must be taken to discuss fatigue from a holistic 
perspective so that we can integrate different components of fatigue 
into a modern understanding.

AT LEAST TWO FUTURE DIRECTIONS
The future of research into fatigue during exercise points towards two 
potential lines of inquiry. First, there is the question of what we mean 
by the term fatigue. It is now clear that it can mean different things 
to different people. Most obvious here is the point that an organism 
might be said to be “fatigued” according to a wide range of criteria. 
However, perhaps, a more fundamental point is that fatigue can refer 
to both states and processes and that these need to be considered 
both separately and synergistically. Clearly, there will be times when 
an atomistic or reductive approach to understanding fatigue states 
and processes will be advantageous and other times when new 
knowledge will depend on abandoning the comfort of disciplinary, 
methodological or philosophical specialisation.

A second potential future for fatigue research concerns the kinds of 
questions we are prepared and able to ask. For example, researchers 
interested in what we might broadly call the limits to performance 
are familiar with two widely accepted but incompatible propositions. 
First, there is evidence that without “artificial” aids such as drugs 
or genetic manipulation we are unlikely to see significant future 
improvement in world records for sports such as swimming and 
track and field.25 On the other hand, there are those who point to 
feats of super-endurance, such as those by the first arctic explorers or 
the early trans-continental race walkers, as evidence that we cannot 
really know how far or fast we might go because we are rarely faced 
with circumstances that threaten our very survival.26 Taken together, 
these two propositions beg the question: are the limits to performance 
mechanical and immutable or fuzzy and suggestible? 

One way of managing the tension that is created by these points 
of view is simply to avoid it. For example, we might argue that if 
modern athletes were motivated by the fear of starvation and/or 
death, they would run faster. Of course, this is sheer speculation 
at best. Hypothetically, there is also the problem that this kind of 
“encouragement” might have the opposite effect. Alternatively, we 
might argue that events such as the marathon and, say, walking 1000 
km are both quantitatively and qualitatively different. In other words, 
it is not simply that the 1000-km race is longer than the marathon; to 
put it crudely, it could be that the limits to performance in a 1000-km 
race are predominantly mental, while the limits to performance in 
the marathon are predominantly physiological. This explanation has 
appeal, but there is always the lurking problem of differentiating the 
“mental” from the “physiological”.



24 SAJSM  vol 24  No. 1  2012

A third solution might be to say that it depends on the 
“maturity” of the event. Ergo, in a highly competitive event such 
as the marathon, where lots of people are doing it and the prizes 
for winning are high, we reach the “limits” to performance fairly 
quickly (say, 100 years or so). However, super-endurance races are 
less popular, and, for this reason, we are proportionately much 
further away from the “limits” of performance in them. It is little 
wonder, then, that the limits to performance in this context appear 
to be “mental”. For example, consider the rate of collapse of ultra-
marathon runners after the finish of the race or nearer the times 
to win medals.27

None of these resolutions to the limits of p erformance 
dilemma seem adequate. Perhaps, the problem here is that we 
now find ourselves pushing at a different set of limits the limits 
of the concepts we use and, in turn, the limits they place on the 
questions we are capable of asking. Perhaps, some of the dilemmas 
we currently face concerning the nature of fatigue are an artefact 
of our reliance on concepts like “physiological”, “mental” and 
“psychological”. Are these terms adequate anymore? 

What is clear is that we can no longer pretend that conscious and 
unconscious decision making plays no role in fatigue states and 
processes. This means that studying fatigue as a closed feedback 
loop will no longer suffice. At this stage in our understanding of 
the brain, bringing feedforward mechanisms of the brain into 
fatigue research has the obvious potential to make our work much 
more “fuzzy” and much less “mechanical”. For some, a fuzzy future 
will look too different from the past and make them turn away. 
For others, the possibility of inventing a new conceptual landscape 
with which to investigate/ unravel fatigue beckons.

Patient consent Not needed.

Contributors Each section of the manuscript was written by each 
of the authors.

Provenance and peer review Not commissioned; externally peer 
reviewed.

REFERENCES
1. Dougan A. Raising the dead: the men who created Frankenstein. Edinburgh: Birlinn 

Limited, 2008.

2. Mosso A. Fatigue. London: Swan Sonnenschein & Co Ltd, 1904.
3. Bainbridge FA. The physiology of muscular exercise. 3rd edn. New York, USA: 

Longmans, Green and Co, 1931.
4. Moore B, editor. The Australian concise Oxford dictionary. 4th edn. South Melbourne: 

Oxford University Press, 2004.
5. Edwards RHT. Human muscle function and fatigue. In: Porter R, Whelan J, eds. Human 

muscle fatigue: physiological mechanisms. London: Pitman Medical, 1981:1–18.
6. Bigland-Ritchie B, Furbush F, Woods JJ. Fatigue of intermittent submaximal voluntary 

contractions: central and peripheral factors. J Appl Physiol 1986;61:421–9.
7. Fitts RH, Holloszy JO. Effects of fatigue and recovery on contractile properties of frog 

muscle. J Appl Physiol 1978;45:899–902.
8. Kretchmar RS. What to do with meaning? A research conundrum for the 21st century. 

Quest 2007;59:373–83.
9. Jones D, Round J, de Haan A. Skeletal muscle: from molecules to movement. London: 

Churchill-Livingston, 2004.
10. Noakes TD. Testing for maximum oxygen consumption has produced a brainless 

model of human exercise performance. Br J Sports Med 2008;42:551–5.
11. Robergs RA, Ghiasvand F, Parker D. Biochemistry of exercise-induced metabolic 

acidosis. Am J Physiol Regul Integr Comp Physiol 2004;287:R502–16.
12. Nakamura FY, Soares-Caldeira LF, Laursen PB, et al. Cardiac autonomic responses to 

repeated shuttle sprints. Int J Sports Med 2009;30:808–13.
13. Crewe H, Tucker R, Noakes TD. The rate of increase in rating of perceived exertion 

predicts the duration of exercise to fatigue at a fixed power output in different 
environmental conditions. Eur J Appl Physiol 2008;103:569–77.

14. Ansley L, Robson PJ, St Clair Gibson A, et al. Anticipatory pacing strategies during 
supramaximal exercise lasting longer than 30 s. Med Sci Sports Exerc 2004;36:309–14.

15. Bam J, Noakes TD, Juritz J, et al. Could women outrun men in ultramarathon races? 
Med Sci Sports Exerc 1997;29:244–7. 

16. Weir JP, Beck TW, Cramer JT, et al. Is fatigue all in your head? A critical review of the 
central governor model. Br J Sports Med 2006;40:573–86; discussion 586.

17. Hunter SK, Duchateau J, Enoka RM. Muscle fatigue and the mechanisms of task 
failure. Exerc Sport Sci Rev 2004;32:44–9.

18. Marino FE. Heat reactions in multiple sclerosis: an overlooked paradigm in the study 
of comparative fatigue. Int J Hyperthermia 2009;25:34–40.

19. Duffield R, Coutts AJ, Quinn J. Core temperature responses and match running 
performance during intermittent-sprint exercise competition in warm conditions. J 
Strength Cond Res 2009;23:1238–44.

20. Mock V, Atkinson A, Barsevick A, et al.; National Comprehensive Cancer Network. 
NCCN Practice Guidelines for Cancer-Related Fatigue. Oncology 2000;14:151–61.

21. Gabbett TJ. Influence of fatigue on tackling technique in rugby league players. J 
Strength Cond Res 2008;22:625–32.

22. Royal KA, Farrow D, Mujika I, et al. The effects of fatigue on decision making and 
shooting skill performance in water polo players. J Sports Sci 2006;24:807–15.

23. Enoka RM, Duchateau J. Muscle fatigue: what, why and how it influences muscle 
function. J Physiol (Lond) 2008;586:11–23.

24. Behm DG, St-Pierre DM. Effects of fatigue duration and muscle type on voluntary 
and evoked contractile properties. J Appl Physiol 1997;82:1654–61.

25. Nevill AM, Whyte G. Are there limits to running world records? Med Sci Sports 
Exerc 2005;37:1785–8.

26. Noakes TD. The limits of endurance exercise. Basic Res Cardiol 2006;101:408–17. 
27. Holtzhausen LM, Noakes TD, Kroning B, et al. Clinical and biochemical characteristics 

of collapsed ultra-marathon runners. Med Sci Sports Exerc 1994;26:1095–101.