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Overtraining: how to monitor and how to prevent?
Asker E Jeukendrup
Summary
Overtraining is something that is talked about a lot in sport. Sometimes athletes “overtrain” on purpose for a period of time with the aim to improve their performance in the long term. This is called
“functional overreaching”. It is believed that when such periods are sustained for too long that a long
term pathological situation develops referred to as the ”overtraining syndrome”. There are several
links between nutrition and overtraining. Well-balanced nutrition in combination with well-timed
sports nutrition can help to maintain performance even during periods of hard training. An insufficient or unbalanced diet, on the other hand, may result in deteriorated performance and poor recovery. In
a period of overreaching, a high carbohydrate diet has been shown to reduce symptoms of overtraining
but it cannot completely prevent it. Early detection of overtraining is crucial and there has been an interest in
developing tools and parameters that can be used in the monitoring of training. Amongst the more successful tools
are simple measurements such as questionnaires, sleeping heart rate and regular performance measurements (benchmark sessions).
Introduction
There is considerable debate in the overtraining literature about what overtraining is, how it can be detected, how it
can be prevented and how it can be treated. There are many questions and very few answers mostly because of the fact
that there is very little research. The area is characterised by more review articles than original work. Many people have
an opinion but most information is anecdotal and hardly ever based on well controlled studies (1). Because of this we
even questioned whether overtraining really exists (1). Another problem that makes comparing different studies almost
impossible is the lack of common and consistent terminology in the study of overtraining. Here, the following definitions
will be used.
Figure 1: Definitions
Overtraining
An accumulation of training and/or non-training stress resulting in long-term decrement in performance capacity
with or without related physiological and psychological signs and symptoms of overtraining in which restoration of
performance capacity may take several weeks or months.
Overreaching
An accumulation of training and/or non-training stress resulting in short-term decrement in performance capacity
with or without related physiological and psychological signs and symptoms of overtraining in which restoration of
performance capacity may take from several days to several weeks.
The first thing that becomes obvious from these definitions is that overtraining can be caused by a number of factors
(stresses) other than training. Secondly, these definitions suggest that the difference between overtraining and overreaching is the amount of time needed for performance restoration, and not the type or duration of training stress or the
degree of impairment.
The process by which intensified training and/or limited recovery lead to overreaching or overtraining, is often viewed
as a continuum (figure 2). On the left-hand or beginning of the continuum is the acute fatigue that occurs as a result of
a single training. When single training sessions are applied repeatedly with appropriate recovery, a positive adaptation
and improvement in performance generally occurs. However if the balance between training and recovery is inappropriate, a state of overreaching may develop. If intensified training and limited recovery continues the more serious state of
overtraining or overtraining syndrome may ensue.
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Physiology
Fatigue
Pathophysiology
Overreaching
Overtraining (syndrome)
Figure 2: the fatigue-overreaching-overtraining continuum
According to this continuum, if athletes undergo periods of intensified training in the absence of appropriate recovery,
they may not respond appropriately to the training and progressive fatigue and decreased performance ensues. Once a
state of overreaching has occurred one of two outcomes may follow. Firstly, the athlete/coach/sport scientist may recognise the symptoms associated with overreaching and provide appropriate rest and recovery for the athlete. Following
this, full recovery may occur and the process of overreaching may have stimulated ’supercompensation’ and performance
may increase to a level higher than that previously attained. The second possible suggested outcome following overreaching is the progressive development of a state of overtraining. The reduced performance that occurs as a consequence
of overreaching may be the stimulus for an increase in training in a bid to improve the diminished performances.
Alternatively, the reduced performance may be unrecognised. If high levels of training persist and/or rest and recovery is
inadequate, the more serious state of overtraining is thought to develop. Other contributing stressors include frequent
competition, monotonous training, psychosocial stressors and heavy travel schedules.
Symptoms of overreaching and overtraining are extensive and varied. They are also highly individual and this complicates the issues even more. A selection of commonly reported symptoms can be found in figure 3.
Figure 3: A selection of symptoms associated with overreaching and overtraining
Reduced performance
Washed-out feeling, tired, drained, lack of energy
Mild leg soreness, general aches and pains
Chronic pain in muscles and joints
Insomnia
Headaches
Decreased immunity (increased number of colds, and sore throats)
Decrease in training capacity / intensity
Moodiness and irritability
Depression
Loss of enthusiasm for the sport
Decreased appetite
Increased incidence of injuries
In order to investigate early stages of overtraining we used a model of 7-14 days of intensified training (both intensity
and volume). During this training performance is reduced and various symptoms start to develop. It is important to
realise that performance is the cardinal symptom of overreaching/overtraining as without this symptom the condition
does not exist. Other symptoms include changes in mood state which can be tracked relatively easily with questionnaires
such as the Daily Analysis of Life Demands in Athletes (2). Other indicators that may be useful include sleeping heart rate
(disturbed sleeping patterns and higher average heart rate), lower submaximal and maximal lactate concentrations and
possible a reduction in cortisol response to a standardised exercise bout. Many suggested markers may not be as helpful
as sometimes suggested and may simply respond to fatigue rather than overreaching (3). These markers amongst many
others include cortisol concentration, cortisol/testosterone ratio and creatine kinase.
Muscle glycogen
As overreaching is thought to be brought about by high intensity training with limited recovery, it is perceivable that
the fatigue and underperformance associated with overtraining is at least partly attributable to a decrease in muscle
glycogen levels. Therefore, studies have been performed in a bid to elucidate the role of carbohydrate and dietary intake
on performance after intensified training.
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Costill et al. (4) investigated this possibility by examining the effects of 10 days of increased training volume on performance and muscle glycogen levels. Of the 12 swimmers participating in the investigation, 4 were unable to tolerate the
increase from 4000 metres/day to 9000 metres/day and were consequently classified as non-responders. The group of
non-responders consumed approximately 1000 kcal per day less than their estimated energy requirement and consumed
less carbohydrate than the responders (5.3 g/kg/d vs. 8.2 g/kg/d). However, importantly, muscular power, sprint swimming ability and swimming endurance ability were not affected in either the responders, or the non-responders. Costill et
al. (4) concluded that the glycogen levels of the non-responders were sufficient to maintain performance, but inadequate
for the energy required during training and thus fatigue resulted.
These findings directed Snyder et al. (5) to examine performance responses to intensified training with the addition of
sufficient dietary carbohydrate, in a bid to determine whether overreaching could still occur in the presence of normal
muscle glycogen levels. To ensure sufficient carbohydrate intake, subjects consumed 160g of a liquid carbohydrate in the
two hours following exercise. Subjects completed 7 days of normal training, 15 days of intensified training and 6 days of
minimal training. Resting muscle glycogen was not significantly different when compared between normal training (531
mmol/kg dry weight) and intensified training (572 mmol/kg dry weight). Subjects were reported to be overreached. However maximal power output during an incremental cycle test was not statistically different after intensified training. Only
four of the eight subjects demonstrated both a decline in maximal power output and an increase in responses to questionnaires. Therefore, it appears that in this study only half of the subjects could perhaps be classified as overreached.
Since muscle glycogen depletion is a risk factor for the development of overtraining, nutritional strategies should aim at
optimising glycogen resynthesis during periods of hard training. Amount and timing of carbohydrates and possibly the
coingestion of protein are factors that influence glycogen resynthesis. When carbohydrate supplements are provided
immediately post-exercise, and are ingested at regular intervals providing 1.0-1.5 g/kg per hour this generally results in
the highest glycogen resynthesis rates over a 4-6 hour period.
When carbohydrate supplements are provided immediately post-exercise,
and are ingested at regular intervals providing 1.0-1.5 g/kg per hour this
generally results in the highest glycogen resynthesis rates over a 4-6 hour period
Besides carbohydrate depletion there are other nutritional issues that can increase the risk of developing overtraining.
Dehydration and a negative energy balance can increase the stress response (increased catecholamines, cortisol and
glucagon, while insulin levels are reduced) which can contribute to the risk of developing overtraining. It is a fine balance
because many of these stresses are necessary to obtain the training adaptation necessary for the performance improvements.
Glutamine, overtraining and the immune system
Prof Eric Newsholme and colleagues suggested that hard training and overtraining result in a decreased glutamine
concentration in the blood (8). When the glutamine concentration decreases below a critical level, this could result in
immunosuppression. Indeed, plasma glutamine concentration has been reported to be lower in overtrained athletes. In
a number of studies drops in plasma glutamine levels have been reported in fatigued or overtrained athletes and these
drops have been in the range of 9-40%. On the basis of these thoughts it is often claimed that glutamine supplements
would help reduce immunosuppression after strenuous training and could help to fight overtraining.
However, it is unclear at present if plasma glutamine is a useful biochemical marker of immune function or overtraining, particularly since most of the body glutamine pool is present in muscle (90%) and not in plasma and
because many factors can influence plasma glutamine levels (short term exercise, nutritional status, diet,
infection, trauma).
Branched chain amino acids
In 1987, another hypothesis was launched by Prof. Eric Newsholme in which the amino acid tryptophan was associated with central fatigue (8). Tryptophan is the precursor of 5-hydroxytryptamine
(5-HT or serotonin) in the brain. Only about 10% of the plasma tryptophan is in the free form and
there is evidence to suggest that only this fraction is available for uptake by the brain; the remainder
is bound to plasma albumin, where it shares a binding side with the fatty acids. During exercise, fatty
acids are mobilised from adipose tissue, bind to albumin and tryptophan will be disposed from its binding.
As a result the free tryptophan concentration in the blood will rise. Simultaneously, the oxidation of the branched chain amino acids (BCAA) leucine, isoleucine and valine in muscle will increase during prolonged exercise. This
will lead to a decrease of the concentration of the BCAA in the blood. Since BCAA and tryptophan compete for carriermediated entry into the central nervous system by the large neutral amino acid (LNAA) transporter, the increase in this
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ratio would lead to increased tryptophan transport across the blood- brain barrier. Once taken up in the brain, conversion
of tryptophan to 5-HT would occur and lead to a local increase of this neurotransmitter. This increase indeed has been
found in certain brain areas in the rat, but it has not been established whether it also occurs in man.
Prof. Newsholme and colleagues suggested that overtraining can lead to chronically elevated fatty acids levels and a
chronically elevated free tryptophan/BCAA ratio. According to the hypothesis this would lead to increased 5-HT concentrations in the brain and it has been used to explain some of the (central) fatigue symptoms of overtraining.
Although the theory was attractive, the overarching conclusion from a number of studies is that BCAA supplementation
has no effect on performance and although the effect in overtraining has not been directly studied, the efficacy of BCAA
feedings should be questioned.
References
1. Halson SL and Jeukendrup AE. Does overtraining exist? An analysis of overreaching and overtraining research. Sports Med 34: 967-981, 2004.
2. Jeukendrup AE, Hesselink MK, Snyder AC, Kuipers H, and Keizer HA. Physiological changes in male competitive cyclists after two weeks of intensified training.
Int J Sports Med 13: 534-541, 1992.
3. Halson SL, Bridge MW, Meeusen R, Busschaert B, Gleeson M, Jones DA, and Jeukendrup AE. Time course of performance changes and fatigue markers during
intensified training in trained cyclists. J Appl Physiol 93: 947-956, 2002.
4. Costill DL, Flynn MG, Kirwan JP, Houmard JA, Mitchell JB, Thomas R, and Park SH. Effects of repeated days of intensified training on muscle glycogen and swimming performance.
Med Sci Sports Exerc 20: 249-254, 1988.
5. Snyder AC, Jeukendrup AE, Hesselink MK, Kuipers H, and Foster C. A physiological/psychological indicator of over-reaching during intensive training.
Int J Sports Med 14: 29-32, 1993.
6. Achten J, Halson SL, Moseley L, Rayson MP, Casey A, and Jeukendrup AE. Higher dietary carbohydrate content during intensified running training results in
better maintenance of performance and mood state. J Appl Physiol 96: 1331-1340, 2004.
7. Halson SL, Lancaster GI, Achten J, Gleeson M, and Jeukendrup AE. Effects of carbohydrate supplementation on performance and carbohydrate oxidation after
intensified cycling training. J Appl Physiol 97: 1245-1253, 2004.
8. Newsholme EA, Parry-Billings M, McAndrew N, and Budget R. A biochemical mechanism to explain some mechanisms of overtraining.
In: Advances in nutrition and topsport, edited by Brouns F. Basel: Karger, 1991, p. 79-93.
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