Overtraining is a term often heard in endurance circles but just how concerned should you be about this condition?

Given that just about every serious athlete or active individual dreads this condition it is important to know just how much training is too much.

Before delving into the topic, it is important to understand that training load relates to volume as well as intensity.

However, basic overtraining or overtraining syndrome – an imbalance between training and recovery leading to symptoms associated with neuroendocrine dysfunction – is more complex than that simple distinction.

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Individual difference

First and foremost, everyone is different. We all have different physiologies and genetic make-ups.

According to Ian Craig, BSc MSc CSCS, an exercise physiologist, nutritional therapist and sports coach, we also have vastly differing training histories, and are all exposed to varying types of lifestyle stressors and degrees of stress.

“This all has a bearing on how much training can lead to overtraining. As such there is no simple, straightforward answer to the question ‘how much training is too much?’”

To understand how a person can become overtrained, it is critical to understand the physiological responses our bodies have to various stressors, be it physical stress from exercise, mental stress from work or emotional stress.

Craig makes reference to the work of Dr. Alex Concorde, a renowned immunologist, who refers to the three Ps of stress:

  1. Psychological
  2. Physiological
  3. Physical.

“Training, a manual job, biomechanical dysfunction from extended periods of sitting, diet-induced stress and life stress all interact seamlessly to create an environment conducive to overtraining.”

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Managing stress

And it’s not just the amount of stress that matters, it’s also important how we deal with it. For instance, elite athletes can engage in the volume and intensity of training required to compete at that level as their lives are structured around training and recovery.

They have the time to get the correct amount of rest and sleep their bodies require, see the physio or go for regular massages. They also have access to the best advice and coaching, and their nutritional needs are met with personalised diet plans and the best quality supplementation. Athletes who are fully sponsored don’t have to worry about financial stress either.

“On the other hand, weekend warriors or amateur athletes have to deal with the stress of balancing work, home life and training, which means that overtraining should certainly be of concern to them,” states Craig.

Any athlete has the potential to break down their bodily systems, specifically their muscular, neurologic, endocrine and immune systems through the combination of excessive exercise, lifestyle-related stress and other environmental stressors. And this holds true for any level of athlete, regardless of their experience and the base they are coming off,” explains Craig.

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Stress and hormones

This phenomenon is best explained by allostatic load, a biological framework concept proposed by Bruce S. McEwen Ph. D and Eliot Stellar Ph. D in 1993.

Simply stated, allostatic load refers to “the wear and tear on the body” caused by exposure to repeated or chronic stress.

Craig explains that excessive physical activity and exercise can be classified as a type of allostatic load as stress is imposed on various systems in the body. This stress initiates various catabolic processes and the overtrained state this leads to can be classified as either parasympathetic overtraining or sympathetic overtraining.

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Different types of overtraining

Parasympathetic overtraining results in a state in which your body is chronically trying to repair itself, while sympathetic overtraining results in a hormone imbalance that cascades down affecting other endocrine systems, and eventually the neurological system too.

“The effects of stress on the endocrine system are particularly important in this regard, most notably the hypothalamic-pituitary-adrenal (HPA) axis,” he says.

The hypothalamus and pituitary gland, both located in the brain, and the adrenal glands, located at the top of the kidneys, work together to regulate much of the endocrine system, controlling important functions such as your body’s response to stress, your mood, digestive function, immune response, libido, metabolism and energy levels.

Overtraining is one of the quickest ways to create imbalances in your HPA axis,” continues Craig.

“It’s important to understand that, like most endocrine systems in your body, the HPA axis operates on a feedback loop. When there is an initial over-expression of a hormone such as excessive cortisol production caused by chronic stress and/or excessive exercise this feedback loop ceases to function properly.”

The increased demands placed on the endocrine system will eventually lead to endocrine fatigue and associated conditions such as adrenal insufficiency (reduced production of steroid hormones, particularly cortisol).

This, in turn, can lead to neural fatigue and failure if stress levels are not addressed as these systems are intertwined.

It is when you down-regulate endocrine function in this manner that you start experiencing symptoms associated with overtraining such as fatigue, exhaustion, suppressed immune function, loss of appetite, impairment of psychological processing, biochemical dysfunction, decreases in performance and a lack of adequate adaptation to exercise, and even detraining in certain instances.”

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A sweet spot

According to Craig, it has been shown that there is a “sweet spot” in the HPA axis that promotes health and vitality, which is achieved through moderate amounts of training.

“However, this is a different value for everyone and is not merely a factor of the amount and intensity of exercise you do. It is when the total amount of stress on an athlete, including their training load, exceeds their body’s capacity to cope and recover when overtraining occurs.”

Craig goes on to clarify that there is a degree of high intensity and/or high volume training required to improve. “It is the time spent pushing boundaries that will elicit an adaptive response to training.

However, if you train at this level over a prolonged period of time it will down-regulate the endocrine system, which is why periodisation and cycled training are essential, and why other lifestyle stress factors need to be considered. It is for this reason that not listening to your body can prove to be extremely detrimental.

Finding the balance

As such, those athletes and active individuals who always work to a schedule and try to hit certain distances each week are more likely to become overtrained.

“You need to listen to your body and don’t push through fatigue or feelings of tiredness.”

With so many factors in the equation it may seem overly complicated to determine how hard you should hit your next training session.

However, there are various tools you can use to determine your current stress levels, some of which are largely subjective, while others offer an objective view based on specific biofeedback measurements.

A subjective approach would be rating your mood, sleep quality, levels of fatigue on waking or your general willingness to train. The recurrence of illness, especially upper respiratory tract infections may also be a good indicator of overtraining. If you prefer to be more precise you can look at measurable physical factors such as your resting heart rate, heart rate variability, your waking body temperature or use lab tests to directly measure circulating stress hormone levels,” says Craig.

Other signs and symptoms of parasympathetic overtraining may include severe fatigue, insomnia, lost libido, chronic tiredness, low motivation levels, a low resting heart rate, and low blood pressure. Sympathetic overtraining, on the other hand, may present as irritability, restlessness, poor sleep quality, weight loss, poor performance and lost libido.