Brain neurotransmitters in fatigue and overtraining

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The below may be of interest:

Brain neurotransmitters in fatigue and overtraining

http://findarticles.com/p/articles/mi_7393/is_5_32/ai_n32052893/?tag=content;col\

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by Romain Meeusen, Philip , Hiroshi Hasegawa, Bart Roelands, F.

Piacentini

Abstract: Since the publication of the serotonin hypothesis, numerous theories

involving the accumulation or depletion of different substances in the brain

have been proposed to explain central fatigue. Although the theoretical

rationale for the " serotonin-fatigue hypothesis " is clear, several seemingly

well-conducted studies have failed to support a significant role for

5-hydroxytryptamine in the development of fatigue.

As brain function appears to be dependent upon the interaction of a number of

systems, it is unlikely that a single neurotransmitter system is responsible for

central fatigue. Several other mechanisms are involved, with evidence supporting

a role for the brain catecholamines.

Fatigue is therefore probably an integrated phenomenon, with complex interaction

among central and peripheral factors. When prolonged and excessive training

happens, concurrent with other stressors and insufficient recovery, performance

decrements can result in chronic maladaptations that can lead to the

overtraining syndrome (OTS). The mechanism of the OTS could be difficult to

examine in detail, perhaps because the stress caused by excessive training load,

in combination with other stressors, might trigger different " defence

mechanisms " such as the immunological, neuroendocrine, and other physiological

systems that all interact and probably therefore cannot be pinpointed as the

" sole " cause of the OTS.

It might be that, as in other syndromes, the psychoneuroimmunology (study of

brain--behavior--immune interrelationships) might shed a light on the possible

mechanisms of the OTS, but until there is a definite diagnostic tool, it is of

utmost importance to standardize measures that are now thought to provide a good

inventory of the training status of the athlete. It is very important to

emphasize the need to distinguish the OTS from overreaching and other potential

causes of temporary underperformance such as anemia, acute infection, muscle

damage, and insufficient carbohydrate intake.

Conclusions

Brain neurotransmitter systems are clearly involved in regulating the genesis of

fatigue during exercise. It seems unlikely that a single neurotransmitter system

is responsible for central fatigue. Therefore much more research is necessary

before we can draw definitive conclusions. We need to develop standard

experimental strategies to examine the effects of exercise on brain functions.

Neurotransmitter interrelationships are important since these interactions

reflect the multidimensional image of the different processes that happen in the

brain during exercise, training, and possibly OTS.

The physical demands of intensified training are not the only elements in the

development of the OTS. It seems that a complex set of psychological factors are

important in the development of the OTS, including excessive expectations from a

coach or family members, competitive stress, personality structure, social

environment, relationships with family and friends, monotony in training,

personal or emotional problems, and school- or work-related demands. Although no

single marker can be taken as an indicator of impending OTS, the regular

monitoring of a combination of performance, physiological, biochemical,

immunological, and psychological variables would seem to be the best strategy to

identify athletes who are failing to cope with the stress of training.

Much more research is necessary to get a clear-cut answer to the origin and

detection of the OTS, and there is a need for studies with new noninvasive

methods to investigate local metabolic responses induced by the OTS. We

therefore encourage researchers and clinicians to report as much as possible on

individual cases of athletes who are underperforming and who, by following the

exclusion diagnosis, are possibly suffering from the OTS.

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Carruthers

Wakefield, UK