Now we have a better idea of the definition of overtraining, it is important to discuss the symptoms and what causes them...
What does the research say?
For many years, the prevailing theory was that there were two different types of overtraining: a parasympathetic and a sympathetic form. A situation of hyperactivity was followed by a period of insensitivity. Hypothalamic dysfunction (a disturbance in the normal functioning of the hypothalamus) was believed to be at the origin of the switch from one form to the other.
A brief summary...
Various stresses (including too much training) bring the body in a state of alertness: stress hormones are high all the time and this can interfere with a number of processes in the body. For example increased levels of stress hormones (especially cortisol) have been shown to impair immune function and increases in adrenaline (epinephrine), may interfere with normal sleep. This causes the symptoms of the “sympathetic form of overtraining”. When this situation persists for a long period of time, the body may respond by becoming less sensitive to these stress signals and this is where full scale overtraining might develop. Symptoms can be very similar between these two forms of overreaching/overtraining, but once the body becomes insensitive to stress signals it will take much longer to recover. This was referred to as the parasympathetic form of overtraining. It has also been suggested that once your body becomes desensitized the symptoms become less severe, even though this a much more serious and unhealthy situation.
Effects on performance...
It is important to note that the most important symptom of overtraining (or overreaching) is decreased performance. Without a clear and objective reduction in performance, overtraining cannot be present. This is important because many studies that claim to have investigated “overtraining” did not actually measure performance and therefore have no way of knowing if the athletes in their study were actually overreached or overtrained.
"The most important symptom of overtraining is decreased performance. Without a decrease in performance there cannot be overtraining"
What are the other symptoms?
The second series of symptoms in the figure are fatigue related (this is related to performance but more subjective). A third category of important symptoms are disturbances in behaviour and mood. This category is important because these are easy symptoms to pick up, especially for people that surround the athletes. It is common to see athletes become irritable and show signs of depression when training load is dramatically increased. Performance, fatigue and mood state are usually inexpensive to measure and monitor but provide very good indicators of overreaching or overtraining.
Performance, fatigue and mood state provide very good indicators of overreaching or overtraining
What are other indicators of overtraining?
In addition physiological measurements like heart rate (especially during sleep) can sometimes be helpful. Blood measurements are often recommended as preventative measures but studies have not shown one clear marker that can predict overreaching or overtraining. The most common markers are testosterone and cortisol and the cortisol/testosterone ratio. CK is often measured as well as Interleukin-6 or glutamine. However, none of these markers have been shown to be particularly meaningful.
In the 1980 and 1990s it was more common to measure various hormones. This could provide evidence for the existence of the sympathetic or parasympathetic form of overtraining. Drug challenge tests were developed where a drug was administered to trigger a hormone response. The idea was that of the hormone response was abnormal this could be an indication of overtraining. These tests were not only impractical (and perhaps unethical), they also did not prove to be very useful.
Finally, in the figure above you can see that there are a number of symptoms that are often seen with different levels of severity: sleep disturbances and insomnia, frequents colds that seem to linger and loss of appetite in combination with weight loss. It is obvious that overtraining is a complex phenomenon that affects many systems in the body and therefore results in a wide range of symptoms.
Take home messages:
Overtraining and overreaching are characterized by a wide range of symptoms
These symptoms are HIGHLY individual. Different athletes will show different symptoms with different levels of severity.
No single symptom is unique to “being overtrained".
There may be different forms of overtraining but supporting evidence is scarce at best. Therefore the definitions used in a previous aricle (overreaching/overtraining), should be used.
Some of the symptoms in milder forms may be early indicators of overtraining (see Prevention of Overtraining - coming soon).
Halson & Jeukendrup Sports Med. 2004;34(14):967-81