There is much written about overtraining and it is a frequent topic of conversation amongst coaches, trainers and athletes. Although everyone probably has some idea what overtraining is, when you start to ask questions, it becomes clear pretty quickly that people have different ideas about overtraining, what causes it, how it is monitored and prevented, and even whether it is a good thing or not.
There are a lot of publications on the topic and even books dedicated to it. I will post a number of articles on the topic, discussing symptoms as well as possible preventative measures, but first we must all be very clear on what we mean by the term overtraining.
The term overtraining is used in a variety of ways and the most common way is as a verb indicating “performing too much training”. “I am overtrained“, when used in this context, means “I have trained too much”. However, this is not the most common definition used by scientists. Overtraining here is often used to indicate a situation where the athletes suffers from underperformance and there is no obvious reason to explain this. Usually the athlete has tried to recover more with no success and/or to train harder with no success. The underperformance is accompanied by a host of symptoms. These symptoms are diverse and highly individual, meaning that different athletes may show completely different symptoms. Because of the complex nature of the clinical symptoms the term "overtraining syndrome" is often used. In a review article with the title “Does overtraining exist?” that Dr Shona Halson and I wrote several years ago we discussed the defined overtraining or the overtraining syndrome not on the basis of the performance decrement or the symptoms but the duration of the recovery.
Performance decrements are common, but this can simply be due to fatigue. Or it can be because of extreme fatigue, often referred to as overreaching, which is observed usually after a block of hard training or a training camp. Athletes who come back from a training camp usually perform worse at first, but after sufficient recovery typically see a major jump in their performance as the reward for the hard work during the camp. Overreaching had therefore been described as functional overreaching. (The term functional overreaching was described in a consensus paper by Professor Romain Meeusen from the Free University in Brussels and colleagues from various Universities all over the world). Athletes go through a phase like this because it is necessary to improve.
Thus overtraining seems to be at the far end of a spectrum of different forms of “fatigue”. On one side of the spectrum we find fatigue: a performance decrement which can be reversed with a few hours of rest. Severe fatigue may take 24 or 48 hours to recover from. When this fatigue gets really severe, usually after several days or weeks of training and it may take weeks to recover, we refer to this as overreaching. Typically this is a functional form of overreaching because athletes embark on such a program to cause extreme fatigue with the end goal to improve their performance. On the other end of the spectrum we have the overtraining syndrome that is very difficult to recover from, has a large range of symptoms and is not functional but rather pathological. The overtraining syndrome could mean the end of a season or even the career of an athlete.
From a scientific point of view as we move from left to right on this spectrum we have less and less data to support any theory. There is a large amount of information about the causes of fatigue, at the muscle level as well as the level of the brain. It is clear that fatigue is a multifaceted phenomenon and although there still is a lot of debate about the different factors and which factors play the most important role, we have a lot of data to tap into. This is not the case with overreaching. There are only a few controlled studies. Many of the studies that have investigated periods of hard training did not measure performance and can therefore not draw any conclusions about overreaching where decreased performance is the key symptom. The well controlled studies can probably be counted on two hands. When we get to overtraining, there really isn’t any solid data. There are some case reports and a lot of anecdotal information. Above all there are a lot of theories. But the nature of the syndrome makes it impossible to study it systematically.
When athletes are asked if they have been overtrained during their career, most athletes will probably say that they have been overtrained at some point in their careers, but was this really overtraining as we defined it here? This is why the title of the paper we wrote was “Does overtraining exist?”. It may exist, but there is little data to go by.
Halson & Jeukendrup Sports Med. 2004;34(14):967-81
Meeusen et al MSSE 2013 45(1):186-205