Overtraining Syndrome (OS) is a term used to define the symptoms of muscle fatigue and weakness that occur after prolonged periods of intense exercise. These symptoms are often accompanied by other physical complaints such as headaches, nausea, dizziness or even hallucinations. OS may result in significant impairment in one’s ability to perform at their previous level, resulting in reduced performance and/or increased injury rates. 
The first stage of overtraining is known as acute OS and occurs when the athlete experiences signs of muscle fatigue within a short period of time after training. During this phase, the athlete may experience some symptoms such as headache, loss of coordination, nausea and vomiting. However these symptoms are temporary and resolve themselves with rest.
The second stage of overtraining is known as chronic OS and occurs when the symptoms persist for longer than two weeks after training. At this point, the athlete may experience severe muscle fatigue, depression, anxiety and other psychological problems. The third stage of overtraining is known as terminal OS and occurs when the symptoms have persisted for six months or more after training. At this point, there is no cure available for the condition.
Although the exact cause of overtraining is not known, some contributing factors have been identified. Overtraining usually occurs when an athlete increases the intensity or duration of their training program without allowing for a gradual increase in physical demands. In addition, some studies suggest that excessive levels of stress may impair training adaptations and even result in reduced performance. It is possible to overtrain even if you’ve only increased your training volume slightly.
It is also possible to overtrain by only increasing the intensity of your training, without modifying the volume.
Athletes who experience overtraining typically train at a high level for several years. For example, many swimmers begin intensive training at a young age and often continue through their high school and university swimming programs. In addition, many elite swimmers will continue to swim competitively into their 30s. As a result, these factors can all contribute to overtraining in some way or another.
The excessive training that leads to overtraining generally involves high intensity exercise or extended endurance training. As a result, there is evidence that some people are more inclined to suffer from overtraining than others. In addition, other factors such as a previous illness or infection, can also contribute to the onset of overtraining.
Overtraining is also more likely to occur when the athlete does not consume a nutritious diet or have sufficient rest. In addition, heavy alcohol consumption and/or cigarette smoking can decrease the body’s natural defences and make overtraining more likely. Sleeping disorders and psychological issues such as stress and anxiety are other factors that may contribute to overtraining.
Overtraining occurs when an athlete increases training volume or intensity without allowing for proper recovery. When this occurs, various symptoms may appear which can impair physical and mental performance. An athlete suffering from overtraining may experience extreme fatigue, muscle loss, changes in psychological state, decreased performance in sport and an increase in injuries that require time to heal. It is therefore important that athletes monitor their training to ensure that they do not overtrain.
Overtraining is not an actual medical condition but rather an imbalance between training and recovery. As a result, it is sometimes referred to as ‘overtraining syndrome’.
How can I avoid overtraining?
If you think that you may be suffering from overtraining, you should immediately reduce the intensity and/or duration of your training. Make sure that you give your body adequate time to rest and recover between sessions. It may also help to seek professional advice from a sport psychologist or a sports physician.
Sources & references used in this article:
Acquisition of a novel behavior induces higher levels of Arc mRNA than does overtrained performance by MP Kelly, SA Deadwyler – Neuroscience, 2002 – Elsevier
Heart rate variability, blood pressure variability, and baroreflex sensitivity in overtrained athletes by M Baumert, L Brechtel, J Lock… – Clinical Journal of …, 2006 – journals.lww.com
Overtraining, excessive exercise, and altered immunity by LL Smith – Sports medicine, 2003 – Springer
Biochemical and immunological markers of over-training by M Gleeson – Journal of sports science & medicine, 2002 – ncbi.nlm.nih.gov
The role of psychological characteristics in facilitating the pathway to elite performance part 2: Examining environmental and stage-related differences in skills and … by Á MacNamara, A Button… – The sport …, 2010 – journals.humankinetics.com
Periodized Programs-Part 2 by R Orr – Personal Training on the Net, 2005 – ptonthenet.com