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Overtraining Syndrome Symptoms and Diagnosis in Athletes:
Where Is the Research? A Systematic Review
Jonathon Weakley,
1,2,3
Shona L. Halson,
1,2
and I ˜nigo Mujika
4,5
1
School of Behavioural and Health Sciences, Australian Catholic University, Brisbane, QLD, Australia;
2
Sports Performance, Recovery, Injury and
New Technologies (SPRINT) Research Centre, Australian Catholic University, Brisbane, QLD, Australia;
3
Carnegie Applied Rugby Research (CARR) Centre,
Carnegie School of Sport, Leeds, United Kingdom;
4
Department of Physiology, Faculty of Medicine and Nursing, University of the Basque Country,
Leioa, Basque Country;
5
Exercise Science Laboratory, School of Kinesiology, Faculty of Medicine, Universidad Finis Terrae, Santiago, Chile
Context:To understand overtraining syndrome (OTS), it is important to detail the physiological and psychological changes that
occur in athletes. Objectives:To systematically establish and detail the physiological and psychological changes that occur as a
result of OTS in athletes. Methods:Databases were searched for studies that were (1) original investigations; (2) English, full-text
articles; (3) published in peer-reviewed journals; (4) investigations into adult humans and provided (5) objective evidence that
detailed changes in performance from prior to the onset of OTS diagnosis and that performance was suppressed for more than 4
weeks and (6) objective evidence of psychological symptoms. Results:Zero studies provided objective evidence of detailed
changes in performance from prior to the onset of OTS diagnosis and demonstrated suppressed performance for more than 4
weeks accompanied by changes in psychological symptoms. Conclusions:All studies failed to provide evidence of changes in
performance and mood from “healthy”to an overtrained state with evidence of prolonged suppression of performance. While
OTS may be observed in the field, little data is available describing how physiological and psychological symptoms manifest.
This stems from vague terminology, difficulties in monitoring for prolonged periods of time, and the need for prospective testing.
Real-world settings may facilitate the collection of such data, but the ideal testing battery that can easily be conducted on a regular
basis does not yet exist. Consequently, it must be concluded that an evidence base of sufficient scientific quality for understanding
OTS in athletes is lacking.
Keywords:OTS, physiological, psychological, recovery
Overtraining syndrome (OTS) is a condition associated with a
long-term imbalance between training and recovery.
1
First reported
in the scientific literature in the 1930s,
2
it is characterized by
performance decrements, fatigue, and mood disturbances and has
been proposed to affect between 20% and 60% of athletes through-
out their careers.
3–6
Compared to functional and nonfunctional
overreaching, OTS is the most severe condition and reflects a
chronic accumulation of training and nontraining stressors that can
take months to years to fully recover from.
7
However, the patho-
physiology of this condition is still poorly understood, with the
evaluation of a range of psychological, biochemical, immune,
neural, and neuroendocrine measures commonly assessed with
little success.
8–11
Additionally, inconsistencies in the terminology
and diagnosis of OTS has likely contributed to the poor under-
standing of this phenomenon, and information regarding the effects
of true OTS in elite populations is exceedingly limited.
OTS is defined as “a sports-specific decrease in performance
together with disturbances in mood state. Underperformance per-
sists despite a period of recovery lasting weeks or months.”
12
Because of this ambiguous definition, OTS is a vague concept.
While often considered a more extreme version of overreaching,
consensus definitions imply that the main difference between OTS
and overreaching is the amount of time needed for performance
restoration.
7
However, difficulty lies in the subtle difference that
might exist between nonfunctionally overreached athletes and
those experiencing OTS. Additionally, the inclusion of mood or
psychological changes has not always been used in definitions.
7,12
It is difficult to comprehend that such severe fatigue that causes
prolonged, yet transient performance decrement would not induce
some form of psychological signs or symptoms. Thus, the vague
terminology and uncertainty that stems from existing definitions
makes identifying literature that provides objective evidence on
OTS difficult.
Due to the severe and complex nature of OTS,
13
understand-
ing, diagnosing, and treating the syndrome has been difficult. Very
little published data in elite athletes is available and, despite being
less extreme, and potentially having similar functional outcomes,
inferences from athletes who are experiencing overreaching are
commonly used to insinuate outcomes of OTS. This lack of
information may be due to the difficulties associated with OTS
research, including the inability to ethically induce a state of
overtraining, the need for consistent monitoring prior to and during
the overtraining state to validate a performance decrement, and the
likely multifaceted nature of the syndrome.
14
Despite this, it is
commonly discussed throughout the sports science literature and
the general sports community, and a concerted effort has been
made to understand the mechanisms and associated symptoms.
Considering the proposed severe consequences and substan-
tial literature on OTS, it is important to understand its effects on
athletic performance, physiological changes, and psychological
signs and symptoms. Furthermore, to better understand the
etiology of the syndrome, it is prudent to detail the physiological
changes and psychological symptoms that occur when an athlete
becomes overtrained. Therefore, the aim of this systematic review
was to establish and detail the objectively demonstrated physio-
logical and psychological changes that occur as a result of OTS in
athletes.
Weakley (Jonathon.weakley@acu.edu.au) is corresponding author
1
International Journal of Sports Physiology and Performance, (Ahead of Print)
https://doi.org/10.1123/ijspp.2021-0448
© 2022 Human Kinetics, Inc. BRIEF REVIEW
First Published Online: Mar. 23, 2022
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Methods
Search Strategy
Following Preferred Reporting Items for Systematic Reviews and
Meta-Analyses guidelines for systematic reviews,
15
the academic
databases SPORTDiscus, Web of Science, Scopus, and MEDLINE
were systematically searched in June and December of 2021 to
identify English-language peer-reviewed original research studies
that investigated OTS as defined by Urhausen and Kindermann.
12
Due to differences in database design, studies were identified by
searching “abstracts, titles, and key words”in Scopus; “All Text”in
SPORTDiscus and MEDLINE; and “All Fields”in Web of Sci-
ence. Additionally, the following Boolean search string was used:
(overtrain* OR over-train* OR overreach OR staleness) AND
(underperformance OR under performance OR underrecovery
OR under-recovery OR “under recovery”) (full search strategy
for each database can be found in Supplementary Material 1
[available online]). Medical Subject Headings were not used
when searching the MEDLINE database and the protocol was
not peer reviewed prior to submission. All search results were
extracted and imported into a reference manager (EndNote 20,
Thomson Reuters, Philadelphia, PA). A systematic review protocol
that includes the review question, search strategy, exclusion crite-
ria, and risk of bias assessment was registered on September 2,
2021, with the Open Science Framework (osf.io/45zwp).
Selection Criteria
All duplicate studies were removed, and the titles and abstracts of
all remaining studies were independently screened for relevance by
2 authors (J.W. and S.L.H.). Studies that were deemed beyond the
scope of the review were removed. Disagreements were resolved
through discussion or via a third researcher (I.M.). The full text of
the remaining studies were then assessed for eligibility. To be
eligible for inclusion, studies were required to (1) be original
research investigations; (2) be full-text articles written in English;
(3) be published in a peer-reviewed academic journal; (4) be an
investigation into adult humans; (5) provide objective evidence that
details changes in performance from prior to the onset of OTS
diagnosis (ie, “healthy”), and that performance was suppressed
for more than 4 weeks; and (6) provide objective evidence
(eg, validated questionnaire) of psychological symptoms of mal-
adaptation. If it was deemed that a study did not meet the inclusion
criteria, it was excluded from the analysis. The reference lists of all
full-text screened studies were manually searched for any studies
that were not retrieved in the initial search. If any studies were
identified through this manual search strategy it was subjected to
the same assessment as previously described. Outcomes that were
recorded were any objectively demonstrated physical and psycho-
logical change that occur as a result of OTS. Finally, it should be
noted that 4 weeks of performance suppression was deemed
necessary as periods shorter than this are commonly used to
facilitate the realization of physical capacities during, for example,
normal overreaching-tapering or altitude training strategies in
athletes. Additionally, due to the severe and chronic nature of
OTS, the requirement of both physical performance suppression
and psychological changes were considered appropriate.
Assessment of Reporting Quality
The reporting quality of the research was assessed using a modified
version of the Downs and Black checklist.
16
This method is valid
for assessing the methodological reporting quality of observational
study designs and has previously been used by systematic reviews
pertaining to sport science.
17,18
Study quality was assessed against
9 items, scored on a scale from “0”(unable to determine, or no) to
“1”(yes). In total, a score of “9”was indicative of the highest study
quality.
Results
Identification of Studies
The systematic search retrieved a total of 768 studies with a further
10 manuscripts found through screening of reference lists. One
hundred and sixty-one of these were removed as duplicates. The
titles and abstracts of the remaining 768 studies were screened, with
42 manuscripts being retrieved for full-text screening. However,
zero studies were identified that met the inclusion criteria. Because
of this, questions 12 to 15 of the Preferred Reporting Items for
Systematic Reviews and Meta-Analyses guidelines could not be
completed. The identification process is outlined in Figure 1.
Research Reporting Quality
As no studies met the inclusion criteria, the methodological
reporting quality could not be reported.
Study Characteristics
No studies met the inclusion criteria of this review; this was largely
attributed to no study providing objective evidence of performance
changes from a “healthy”state combined with evidence of suppres-
sion of performance that lasted 4 weeks or longer. It should be noted
that several studies
8–10,14,19–29
did state that performance had
declined; however, evidence of the magnitude or the length of
decline was not provided. Furthermore, studies occasionally stated
that psychological changes had occurred, but this was not corrobo-
rated with objective evidence (eg, a validated scale).
30
Therefore, as
no study provided actual evidence of objective changes in physical
performance and psychological states, as required by the definition
of purportedly overtrained athletes, we were unable to describe the
physical and psychological changes that occur with OTS.
Discussion
The aim of this systematic review was to establish and detail the
physiological and psychological changes that occur as a result of
OTS in athletes. From the search of the literature, no studies met the
criteria and definition of OTS, with all studies failing to provide
evidence of changes in physical capacity from a “healthy”to an
overtrained state with chronic (ie, ≥4 wk) suppression of perfor-
mance. This suggests that, while OTS may be a severe condition
that can negatively affect athletes, for practitioners and researchers,
there is little data available that describes how physical and
psychological qualities manifest (Figure 2). These issues likely
stem from the vague terminology that has traditionally been used to
define OTS, the difficulties of providing objective evidence of
performance across prolonged periods of time, and the prospective
nature of testing that would be required for diagnosis. It should be
noted that while this review cannot provide evidence of sufficient
quality regarding changes in performance and mood state associ-
ated with OTS, it is plausible practitioners and researchers have
indeed observed OTS but have been unable to document these
2Weakley, Halson, and Mujika
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changes. Therefore, it is our recommendation researchers and
practitioners resist the urge to state that OTS has occurred, or
infer similar outcomes, when short-term suppression of perfor-
mance is observed.
A range of factors may be limiting our understanding of OTS.
For example, due to the vague definition and timelines associated
with the syndrome, it is difficult to clearly ascertain the require-
ments and earliest time point at which it can be diagnosed. The
current definition states that “several weeks”of performance
suppression is required. Despite this, it is known that fatigue is
often transient in nature and common tapering strategies last 2 to
4 weeks,
32
while other strategies often used by athletes, such as
altitude training, may suppress performance prior to supercom-
pensation well beyond the time frame associated with OTS.
33
Furthermore, it is hard to fathom that severe training and limited
recovery that causes a transient substantial performance decrement
would not induce negative psychological signs or symptoms.
However, decreases in mood/psychological state are not always
a mandatory inclusion for diagnosis of OTS.
7
Finally, since OTS is
not only associated with the mismanagement of training load but
also external variables,
34
“overtraining”by name is a misnomer.
Biopsychosocial and other factors such as existence of an under-
lying medical disorder, insufficient caloric intake, reduced sleep
quality and/or quantity, and poor mental health likely play a
considerable role in its development and should also be consid-
ered.
22
This has been discussed with the term “unexplained under-
performance syndrome”being suggested to be more appropriate
terminology than “overtraining.”
34
Due to these issues, the litera-
ture to date has considerable inconsistencies in the terminology and
diagnosis of OTS, which has likely contributed to the poor
understanding of this phenomenon.
The lack of information pertaining to OTS is likely an outcome
of the difficulties associated with capturing the necessary data.
With unexplained decrement in performance being one of the
criteria for diagnosis of OTS, several studies have simply stated
that performance has declined when an athlete perceives they are
not performing as well as normal.
19,21
Alternatively, in sports in
which performance is difficult to quantify (eg, wrestling), perfor-
mance has been subjectively assessed by coaches.
35
However,
these methods inherently invite bias and do not objectively assess
change in one of the most important considerations in the defini-
tion of OTS. Further complicating the topic, psychological
Figure 1 —Flow diagram of search strategy for eligible studies.
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symptoms have regularly been reported but this has often been
done without rigor.
30
Within the literature, athletes have been
requested to recall whether a single psychological characteristic
has been altered during their training history. Disregarding issues
surrounding whether an athlete can accurately recall the length and
severity of changes in mood, the ability of a single question to assess
psychological change must be questioned. Considering these con-
cerns, efforts must be made to find valid and reliable objective
methods of quantifying changes in performance and psychological
state that can feasibly assess OTS in a practical setting.
Within the scientific literature, 15 studies have stated or
indicated that objective methods were used to identify suppression
in performance (>2 wk) and psychological symptoms.
8–10,14,19–29
However, these studies did not provide baseline performance
testing data of the athletes included and objective changes in
performance were not detailed. Furthermore, it should be noted
that 12 of these 15 studies analyzed data from the same cohort of
athletes. This indicates that only 4 different cohorts of athletes are
available that have provided objective assessment of performance
and psychological state, with two of these having only one
participant each. While it is praiseworthy that these authors at-
tempted to objectively assess these outcomes and the inherent
difficulties are duly acknowledged, without the provision of data
prior to their diagnosis, practitioners and researchers alike are still
unable to truly understand how OTS manifests.
With the chronic and severe nature of OTS, it could be argued
that elite-level athletes, who complete substantial training loads,
may be at the greatest risk. However, similar to other research in
elite athletes, this inherently brings difficulties. For instance, the
severe nature of OTS coupled with the scarcity of truly elite
populations reduces the likelihood of obtaining data in these
populations. Furthermore, with the growing emphasis on sport
science in elite sport, the mismanagement of fitness and fatigue in
elite athletes may be increasingly rare. Thus, the feasibility of this
type of research in these populations is remarkably difficult. As
practitioners or researchers would not purposely induce OTS in a
group of athletes, it is therefore more likely that individual case
studies from prospective cohorts will be the only feasible method of
attaining an accurate understanding of the expression of OTS in
elite populations. Finally, it should be noted that we recognize that
previous quality research has been conducted in the areas of
intensified training, overreaching, and potential mechanisms in
suspected overtrained athletes that has resulted in an enhanced
understanding of fatigue responses and potential fatigue monitor-
ing tools in the field. However, the challenges in conducting
research that meets the strict criteria necessary for the diagnosis
of OTS, has resulted in a lack of research data that can be translated
to truly elite athletes.
With the diverse range of physical demands that are placed
upon athletes from different sports, signs and symptoms of OTS
distinct to different forms of exercise may be prevalent.
7,31
In
overreached athletes, excessive resistance training volumes and
intensities have been shown to induce different fatigue profiles
when compared to endurance training.
36
Additionally, separate
physical characteristics (eg, strength vs power) have varying
sensitivity to fatigue.
37
Therefore, depending upon the athlete,
their sport, and the physical performance test monitored, the onset
of OTS may occur at differing time points. Furthermore,
while the cause of OTS is commonly acknowledged as multi-
faceted, it is plausible that athletes that incur different demands
also experience different symptoms. Therefore, investigating OTS
as a homogenous outcome that affects all athletes in the same
manner, and attempting to quantify the symptoms of athletes from a
range of athletic endeavors is likely overly simplistic.
To appropriately monitor and quantify the signs and symptoms
associated with OTS, there are several considerations that can
contribute to an accurate reporting of this syndrome. First, there is a
need to establish a baseline in a valid and reliable test that assesses a
relevant physical quality. This is required to verify that a change in
performance has occurred. Second, regular testing must occur to
establish if performance has declined. However, if a state of OTS
has been reached, physically testing an athlete during this time may
be undesirable and exacerbate the fatigue and psychological burden
of the athlete. Third, it must be clearly established that decreases in
performance are not an acute response to previous bouts of training.
Research into tapering and peaking indicates that performance
supercompensation can take up to 4 weeks following the reduction
of training volume and that the timing of supercompensation can
differ between athletes despite identical training loads.
38
Fourth,
any changes in performance must be outside that of the regular
variation associated with the test selected. Fifth, regular testing
throughout the purported overtraining period may be needed to
ascertain the duration of the performance suppression and to
confirm that OTS has occurred. For the understanding and accurate
reporting of OTS, these considerations are necessary but can be
exceedingly difficult in practice.
Practical Applications
A considerable number of issues associated with OTS stem from
the misidentification or lack of verification of the syndrome. To
date, no studies have provided information regarding baseline
physical qualities, evidence of change, and verification of chronic
(ie, ≥4 wk) suppression of performance. Consequently, to improve
understanding, several recommendations can be made that may
help practitioners and researchers. Future research is strongly
recommended to complete a 3-step testing verification process
that involves: (1) testing athletes when they are healthy, (2) testing
again at the initial point of suspected OTS, and (3) testing at least
4 weeks postinitial suspicion. Additionally, tests that are selected
should be relevant to the athlete and changes in performance must
be outside the usual variation of the test used. Furthermore, valid
objective assessment of the athlete’s psychological state is required
and should be assessed at the second or third testing occasion to
verify symptoms of psychological maladaptation.
When designing studies to assess OTS in athletes, there are a
range of ethical and practical considerations. While purposely
inducing a state of OTS in any individual is unethical, in athletes,
it would also be exceedingly impractical. Therefore, while possible,
an accurate understanding of OTS will unlikely be achieved through
controlled trials. Nevertheless, observational data from a range of
real-world settings may enable assessment of this syndrome. For
example, training camps or institutes of sport frequently house
athletes for extended periods of time with testing often completed.
However, follow-up time points to verify diagnosis may be difficult
considering the associated issues with data collection and the
unknown changes that occur with OTS, but these may also provide
some of the best opportunities to collect data on elite athletes.
Conclusions
The multitude of publications on OTS and its severe consequences
for athletes is in direct contrast with the limited availability of
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objective data and diagnostic tools that align with the definition of
OTS. It should be remembered that the key difference between
functional overreaching, nonfunctional overreaching, and OTS is
the amount of time needed for performance restoration and/or
performance supercompensation. Therefore, the diagnosis of
OTS can only be made retrospectively and may be less common
than reported throughout the literature. While measurements of
selected physiological markers may seem appealing, due to the
multifaceted nature of OTS, they may rarely be useful in diag-
nosis. Additionally, their volatility, and the lack of standardized
definitions and procedures that have been used throughout the
literature, reduce our understanding of their mechanistic proper-
ties. Therefore, from a critical review of the existing literature, it
must be concluded that an evidence base of sufficient scientific
quality for the understanding of OTS in athletes is simply
lacking.
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