Overload is considered a key principle of physical training, required for peak performance. However, over-training can result in compromised performance and profound fatigue. Despite the terms chronic fatigue and burn-out often being used to describe over-training, they are actually products of over-training itself, reflecting an overwhelming physiological and pyschological impact on the athlete.
When I swimming, at least from from perspective, rarely were the quantitive biologic and subjective indicators of mood and fatigue assessed in association with the degree of training, as a means to prevent over-training. Yet, we now know that quantitative assessment of the foregoing markers is critical.
Over-training syndrome is a complex combination of interacting physiological and psychological factors caused by excessive training. Current research suggests that despite recognisable clinical symptoms, no single factor or diagnostic tool exists to definitively establish a diagnosis. Nonetheless, a diagnosis can be made by excluding other factors that can degrade performance and mood. These factors include, anaemia, magnesium deficiency, viral infections (e.g. Epstein Barr), muscle damage (characterised by abnormal creatine kinase levels), Lyme disease, endocrinological disorders (e.g. diabetes, thyroid disorders and adrenal disorders), eating disorders, depression, allergies, cardiovascular disease and asthma. Moreover, biological markers indicative of inflammation, such as C-reactive protein, should be evaluated.
Fatigue is a key feature of over-training syndrome, with the capacity for subjective and objective assessment. The subjective state is characterised by both an acute or chronic pattern of tiredness, lethargy, physical and mental weariness and poor concentration. Whereas, objective measures pertain to functional pathology markers including, adrenal hormone profile. It is suggested that such a state of fatigue is responsible for tissue injury, excessive cytokine release and/or oxidative stress. Of particular note is the fact that the fatigue associated with over-training syndrome differs from the fatigue of chronic fatigue syndrome and Epstein Barr Virus given that the athlete continues to train, despite impaired performance. Moreover, after periods of rest, the fatigue resolves.
Despite the underlying causes of over-training syndrome remaining unknown (except for the over-training :)), potential mechanisms for over-training syndrome include oxidative stress, performance induced elevations in serotonin, inadequate carbohydrate or energy intake, and alterations to the parasympathetic and sympathetic nervous system (e.g. catecholamine sensitivity).
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