Overtraining Syndrome

Overtraining, in athletes, is an excessive stress that may produce systemic pathologic consequences, recovery from which requires months or years. Some athletes may develop overtraining syndrome during periods of intense overload training. They may experience a sudden unexplained decline in performance, physiologic dysfunction, or psychologic depression that extends over weeks, months, or even years. The precise causes for such breakdowns are not fully understood, and individual symptoms vary by the type of training. These symptoms cannot be remedied by the procedures normally used for nonpathologic fatigue. The non-pathologic fatigue that may follow one or more exhausting training sessions is usually relieved by a few days of reduced training, or rest, plus a carbohydrate-rich diet.

Symptoms related to overtraining syndrome are subjective and identifiable only after the individual's performance and physiologic function have deteriorated. This makes it very difficult to recognize that a deterioration in performance is caused by overtraining. The underlying causes of overtraining syndrome are often a complex combination of emotional and physiologic imbalances. Primary signs and symptoms12 may include

• General fatigue

• Loss of muscular strength, coordination, and working capacity

• Change in appetite

• Sleep disturbance

• Irritability, restlessness, excitability, or anxiousness

• Loss of motivation and vigor

• Lack of concentration

• Feelings of depression

• Lack of appreciation for things that normally are enjoyable

Hans Selye,13 the founder of stress research, noted as long ago as 1956 that a person's tolerance of stress can break down as often from a sudden increase in anxiety as from an increase in physical distress. The emotional demands of competition, the desire to win, the fear of failure, unrealistically high goals, and the expectations of others can be sources of intolerable emotional stress, which can result in a loss of competitive desire and enthusiasm for training. Armstrong and VanHeest12 made the important observation that overtraining syndrome and clinical depression share similar signs and symptoms, brain structures, neurotransmitters, endocrine pathways, and immune responses. This indicates alterations in the nervous, endocrine, and immune systems in the affected athletes. Physiologic symptoms accompanying the decline in performance often reflect changes in systems that are controlled by either the sympathetic or parasympathetic branches of auto-nomic nervous system.

Sympathetic symptoms from overtraining may include:

• Increased resting heart rate and blood pressure

• Elevated basal metabolic rate

• Loss of appetite

• Decreased body mass

• Sleep disturbance

• Emotional instability

Athletes who emphasize highly intensive resistancetraining methods are more prone to sympathetic symptoms.

Endurance athletes are more likely to suffer from parasympathetic overtraining, and their performance decrements differ markedly from those associated with sympathetic overtraining. These parasympathetic overtraining symptoms may include the following:

• Early onset of fatigue

• Decreased resting heart rate and decreased resting blood pressure

• Rapid heart rate recovery after exercise

The symptoms of overtraining syndrome are particular to the different training regimens of different sports. Thus the concepts of "intensity-related" and "volume-related" overtraining are used to differentiate specific training stressors that produce unique signs and symptoms.14

Of the two conditions, sympathetic overtraining is the one whose symptoms are the most frequently observed. However, some people who are not overtrained develop symptoms associated with the auto-nomic nervous system. For this reason, the presence of these symptoms cannot always be assumed to be result of overtraining.

The endocrine system is definitely involved in the response to overtraining stressors. Athletes with overtraining may show altered blood concentrations of hormone during periods of overloading, which is suggestive of a reaction of endocrine function in response to excessive stress. When volume or intensity of training increases, the blood concentrations of thyroxine and testosterone usually decrease, and that of cortisol increases. The ratio of testosterone to cortisol is thought to regulate anabolic process in recovery; thus a change in this ratio is considered an important sign related to overtraining syndrome. Decreased testosterone coupled with increased cortisol result in more protein catabolism than anab-olism in the cells. Furthermore, most overtraining studies have been conducted on aerobically trained endurance athletes. Hormonal modification during overtraining is complicated, and more research is needed for its interpretation for different individuals and types of training.14 Many experts believe that no blood marker can conclusively define overtraining syndrome.

Armstrong and VanHeest12 proposed that overtraining stressors activate the following two predominant hormonal axes involved in the body's response to stressors: the sympathetic-adrenal-medullary (SAM) axis, which involves the sympathetic branch of the autonomic nervous system, and the hypothalamic-pituitary-adrenocortical (HPA) axis.

This simplified outline is illustrated in Figure 5-4, which shows the interactions of the brain and immune system with these two axes. Thus it is highly likely that brain neurotransmitters play an important role in overtraining syndrome. Levels of serotonin, a major neurotransmitter, are elevated and therefore play a significant role in overtraining, but plasma concentrations of this important neu-rotransmitter do not accurately reflect those concentrations in the brain. In support of Armstrong and VanHeest's12 model, a major role played by cytokines in overtraining syndrome has been pro-posed15: Trauma associated with overtraining in skeletal muscles, bones, and joints causes inflammation and elevates levels of circulating cytokines, which are responsible for the inflammatory response


SAM axis r~


Sympathetic nerves











Anterior pituitary


Adrenal cortex

> r Cortisol

Adrenal cortex

> r Cortisol

Increases arousal

Stimulates energy mobilization/redistribution, increases cardiovascular responsivity

Inhibits immune response and inflammation





Anterior pituitary

Adrenal glands


-Cortisol -

Immune cells

Spleen, thymus, and other immune organs

Figure 5-4 A, The hypothalamus mediates the stress of overtraining through two axes: the hypothalamic-pituitory-adrenocortical (HPA) axis and sympathetic-adrenal-medullary (SAM) axis. B, The brain-immune system interactions mediate the overtraining responses, and the cytokines play a potentially major role in the physiologic processes. ACTH, Adrenocorticotropin; ADR, adrenaline (epinephrine); CRH, corticotropin releasing hormone; fiE, P-endorphin; GH, growth hormone; IL-1, interleukin-1; IL-6, interleukin-6; NA, noradrenaline (norepinephrine); P, substance P; PRL, prolactin; TNF, tumor necrosis factor; Y, neuropeptide Y.

to infection and injury. Excessive musculoskeletal stress from training, if accompanied by insufficient rest and recovery, sets up a cascade of events whereby a local acute inflammatory response evolves into chronic inflammation and eventually into systemic inflammation. Systemic inflammation activates circulating monocytes, which can then synthesize large quantities of cytokines. Cytokines act on the brain and body functions and induce symptoms consistent with those of the overtraining syndrome.

Overtraining, as a stress, certainly affects the normal function of the immune system. This system provides defense against invading bacteria, parasites, viruses, and tumor cells and also actively participates in tissue regeneration after injury. It depends on the actions of specialized cells, such as lymphocytes, granulocytes, and macrophages, as well as antibodies, for neutralizing foreign invaders, the pathogens that might cause illness.

Overtraining suppresses normal immune function, which increases susceptibility to infections and slows down both recovery from fatigue and the healing of injuries. This immune suppression is characterized by abnormally low concentration of both lymphocytes and antibodies. Invading organisms or endogenous conditions, such as bacterial flora and viruses inside the body, are more likely to cause illness when concentrations of active immune cells are low. Also, intense exercise during illness may decrease the ability to fight off infection and increase the risk of more serious complications.16

Overtraining syndrome is a systemic and complex issue that is difficult to diagnose and difficult to treat effectively with conventional procedures. With ISDN, therapy, this syndrome may be prevented and treated more effectively, especially in conjunction with other therapeutic procedures.

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Essentials of Human Physiology

Essentials of Human Physiology

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