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Overtraining Syndrome – What are the more severe and long-lasting effects of doing too much?

Updated: Nov 4, 2022

Training involves a delicate balance between loading the body enough to get fitter and improve performance, but also allowing enough time to recover so your body can get stronger.


To make things simpler, I will not be including a whole lot of information on functional and nonfunctional overreaching. You can view the resources below if you want to learn more about how these differ from Overtraining Syndrome (OTS).


What is Overtraining Syndrome?

Overtraining Syndrome involves pushing the body beyond its limits. It occurs when people don’t respect the amount of rest their bodies need and continue to push through signs that they are doing too much. The chronic stress on the body leads to full-body system changes that impact the nervous system (including the brain) and endocrine system (which is in charge of your hormones) resulting in both physical and psychological changes. These changes impact functioning throughout the day, decrease running performance or lead to an inability to run, and increase recovery time even with low levels of running.


Symptoms of overtraining syndrome (1)

Symptoms of OTS are present in all aspects of someone’s life, not just while running. They involve both physical and psychological changes.


Physical changes:

  • Fatigue

  • Lower or higher heart rate

  • Insomnia

  • Increased blood pressure

  • Restlessness

  • Lack of appetite

  • Weight loss

  • Heavy, sore, stiff muscles

  • Feeling tired in the morning


Mood changes

  • Anxiety

  • Irritability

  • Agitation

  • Depression

  • Loss of motivation

As you can see, there is a lot that goes on with someone who is experiencing OTS. The complexity of OTS makes it hard to diagnose and hard to study in research, making it still a very misunderstood issue (3).


Causes of OTS

What is going on in the body with someone experiencing OTS? The short answer is, we aren’t 100% sure! According to Kreher & Schwartz, 2012, “Currently, it appears that OTS represents a systemic inflammatory process with diffuse effects on the neurohormonal axis affecting host immunology and mood.” In other words, it is a complex issue impacting the pathway that connects our nervous system and hormonal system, leading to physical and psychological changes.


OTS isn’t just caused by doing too much in training, but also is impacted by life changes/stressors. According to the European Joint Consensus Statement on OTS (2), “Several studies have revealed that OTS represents the sum of multiple life stressors, such as physical training, sleep loss, exposure to environmental stresses (e.g., exposure to heat, high humidity, cold, and high altitude), occupational pressures, change of residence, and interpersonal difficulties.” Again, this makes OTS complicated since it is not necessarily due to training alone but can be due to a number of environmental factors on top of training.


Hormone changes with OTS:

There was an interesting study performed by Meeusen et al. (2) comparing hormone levels after exercise in individuals with OTS vs athletes who were approaching OTS. The participants performed two consecutive maximal exercise tests separated by 4 hours and their blood was tested after each bout of exercise to measure a variety of hormone levels: ACTH (regulates cortisol levels), prolactin, and Growth Hormone (this is important for recovery). The point of the study was to look at the neuroendocrine functioning of athletes who weren’t quite at the level of OTS and those who were experiencing OTS.


Here is what they found:

  • In normal healthy athletes, the test reveals an increase in the circulating concentrations of the hormones after both the first and the second exercise bout.

  • Functional overreaching: These are individuals who are in a “productive overtraining” state, where they can back off of training and then achieve fitness gains. The study found that these individuals had a less pronounced neuroendocrine response to a second bout of exercise.

  • Non-functional overtraining: These individuals are experiencing a decrease in sport performance and likely are starting to show signs of OTS but with rest, will recover within weeks to months. The study found that these individuals had markedly higher elevation of hormones after the second exercise trigger

  • OTS: The study found that these individuals had an extremely large increase in circulating hormone concentration after the first exercise bout, followed by a complete suppression in the second exercise bout. This could indicate a hypersensitivity of the pituitary followed by an insensitivity or exhaustion afterward. It’s like your endocrine and nervous system get really tired, just like your muscles do after a hard workout.


Central fatigue and OTS:

Along with impacting the neuroendocrine pathway, individuals with OTS also experience central fatigue. Central fatigue “can be defined as a decrease in the voluntary activation of muscles, directly related to a decrease in the frequency and synchronization of motoneurons, and a reduced drive from the motor cortex.”(5) CNS fatigue impacts the output of the motor cortex in the brain. This part of the brain is in charge of movement. Less activity and firing from this part of the brain impacts performance or even stops the activity all together (5). It also impacts the insula of the brain, which is associated with the sympathetic and parasympathetic activity of the central nervous system, along with volitional exertion of movement (5). So, if this area of the brain is not working properly, it will be difficult to push the effort level while running or running might not be possible at all due to it being a higher-effort movement.