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Overtraining Syndrome – Is it Chronic Fatigue Syndrome for Athletes?

Updated: Jan 5

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 for extended periods of times (months to years). 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), endocrine system (which is in charge of your hormones), and immune system, resulting in both physical and psychological changes. These changes impact functioning throughout the day, decrease running performance or lead to an inability to run altogether, and increase recovery time even with low levels of exercise are performed.

Symptoms of overtraining syndrome (1)

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

Physical changes:

  • Extreme fatigue

  • Lower or higher heart rate

  • Insomnia

  • Increased blood pressure

  • Restlessness

  • Lack of appetite/nausea

  • 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 condition (3).

The symptoms experienced with OTS can present very similarly to Chronic Fatigue Syndrome although the causes are different. The comparison is important because it demonstrates the complexity of the condition and how this isn't just a "running injury." OTS is much more similar to chronic illnesses such as CFS, chronic pain, or Fibromyalgia vs running injuries.

The fatigue experienced by someone with Chronic Fatigue Syndrome or OTS is drastically more than what would be expected for the amount of activity someone does. Someone with these conditions might feel winded after walking up a flight of steps or need to take a nap after going for a casual walk around the block. Someone with OTS might feel extremely sore after running just 1 mile and need to rest for days after very easy activity. Where people with running injuries are still able to other types of exercise, those with CFS or OTS can no longer tolerate any type of exercise.

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.

The name "Overtraining Syndrome" leads to a lot of misinterpretations as to what causes this condition. Running a significant number of miles in a training block is not likely going to lead to OTS. Serial racing in a season also is unlikely to cause OTS. OTS is less about how much someone is running in a week, month, or year and is more about trying to stay in peak fitness for a longer time than the body can handle (typically multiple years). This makes it more of an UNDER-RECOVERY syndrome vs OVERTRAINING syndrome. With that said, OTS isn’t soley caused by running too much, but also is impacted by life changes/stressors and environmental factors. 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 stressors leading to the nervous system and endocrine system being chronically overworked.

Hormone changes with OTS:

The most sound theory of what is going on with a runner experiencing OTS is that there are issues with the Hypothalamic-Pituitary-Adrenal axis. This pathway connects the nervous system to the endocrine system. These areas of the brain and endocrine system are in charge of very basic functioning, such as breathing, hunger, thirst, sleep, blood pressure, mood, growth, metabolism, immune functioning, and response to stress. This theory makes a lot of sense since a lot of these areas are impacted with runners who have OTS.

Let's look at a research study:

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) Central fatigue impacts the output of the motor cortex in the brain. This part of the brain is in charge of voluntary movement. Less activity and firing from this part of the brain impacts performance or even stops the activity all together because it is no longer activating appropriately(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.

Central fatigue doesn’t just impact exercise or physical functioning. It also contributes to the psychological and psychomotor issues that are seen with OTS. Tornero-Aguilera et al. explains it well by stating, “Prolonging an acute state of CNS fatigue can lead to sleep disturbances, depression, pain, the feeling of fatigue, difficulty in maintaining cognitive vigilance, and problems maintaining mental attention” (5). Here you can see that OTS impacts all areas of a runner’s life rather than just their ability to exercise effectively.

CNS fatigue is very complex. It involves many different neurotransmitters impacting the nervous system from the brain all the way down to its connections with individual muscle fibers. To put it simply, central fatigue involves changes in brain biochemistry and nerve-muscle connections leading to a disruption in the nervous system’s ability to tell muscles what to do.

How to assess for Overtraining Syndrome:

This isn’t well established either. There have been a lot of studies on hormone levels, cytokine levels, glycogen/glucose levels, etc and none of them do a solid job of assessing when someone has crossed the line of damaging their body through training vs creating a good amount of stress that the body can adapt to effectively (1,2).

Blood parameters have not been sufficient to diagnose OTS. This includes blood count, C-reactive protein, erythrocyte sedimentation rate, CK, urea, creatinine, liver enzymes, glucose, ferritin, sodium, and potassium, hormone levels, but it is still a good idea to get these areas checked out to rule out issues in these areas (2).

As of right now, the amount of rest it takes to get back to normal is the most established way of knowing if you have OTS. If after months of rest you still do not feel back to normal, then that is a sign that you have crossed the line from helpful training to damaging training.

Treatment for OTS

As of right now, there isn’t a specific treatment for OTS (2). Rest and then a gradual build back into exercising is currently the best way to recover.

How to prevent OTS

  • Track your training: It is important to track how much you are running each day and how much speed work you are incorporating. Doing too much for too long, increasing total volume too quickly, and/or incorporating too much speed training into your training increases the risk of experiencing OTS. Looking at the big-picture of your training calendar is also important. Our bodies cannot maintain peak physical fitness for long periods of time, so it is important to incorporate periods of “down time” in your calendar where you reduce total running volume.

  • Get enough sleep: Enough sleep is important for both physical and psychological functioning and recovery (2).

  • Nutrition: It is important to feed your body well so that your body isn’t in a constant state of deficit. This puts a lot of stress on the body and increases the amount of cortisol (stress hormone) that circulates throughout the body (2). Specifically, taking in enough carbs is important for performing well in training and for effective recovery (2).

  • Change your mindset: Working harder and training harder doesn’t necessarily mean you are getting fitter and faster. Adjusting your mindset to focusing on the importance of training smart and viewing recovery as an important part of reaching your running goals will help you to avoid doing too much.

Best ways to assess for possibly heading down the road of developing OTS

The two biggest areas to help monitor your training and ensure that you are not headed down the road of OTS is rate of perceived exertion and depression…That’s right, not heart rate, blood pressure, or anything else your watch tries to tell you. It is time to listen to your body and mind and recognize changes.

  • Changes in rate of perceived exertion: Here you will notice that any given pace or run FEELS like a lot more effort. Your easy runs might feel fatiguing and your faster or longer runs might not be possible to complete. You might notice that it takes a lot longer to recover between runs even if you run slower or cut runs short.

  • Depression: Depression tends to set in before any physiological symptoms. Monitor for the following – lack of enjoyment in running, lack of enjoyment in typically enjoyable activities, hopelessness, helplessness, worthlessness, difficulty concentrating, low mood, irritability, and fatigue.

  • Other areas to track: Quality of sleep, fatigue levels (during running and outside of running), mood/stress levels, and amount of muscle soreness. If you notice changes in any of these areas, it may be a sign that you are starting to develop OTS.

Want to learn more? Here are some resources to check out:

  1. Kreher & Schwartz, Overtraining Syndrome: A Practical Guide

  2. The European Joint Consensus Statement; Prevention, Diagnosis and treatment of the overtraining syndrome: Joint consensus statement of the European College of Sport Science (ECSS) and the American College of Sports Medicine (ACSM),Prevention%2C%20diagnosis%20and%20treatment%20of%20the%20overtraining%20syndrome%3A%20Joint%20consensus,College%20of%20Sports%20Medicine%20(ACSM)&text=Successful%20training%20must%20involve%20overload,excessive%20overload%20plus%20inadequate%20recovery.

  3. Weakley et al., Overtraining Syndrome Symptoms and Diagnosis in Athletes: Where is the Research? A Systematic Review

  4. Podcast: Science of Ultra – Are you over training?

  5. Tornero-Aguilera et al., Central and Peripheral Fatigue in Physical Exercise Explained: A Narrative Review.

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