An Introduction to Overtraining and Overreaching in Endurance Sport

An Introduction to Overtraining and Overreaching in Endurance Sport

The purpose of exercise training is to provide the body with a stimulus and subsequently, a physiological adaptation. Training volume and loads should be gradually progressed over time, allowing for improvements in performance to take place gradually and without long term ill effect. Subsequently physiological adaptations and progression of training state increase only if the magnitude of change is above the habitual level (current fitness level), and training principles and guidelines of specificity and overload are adhered to.

The apparent limitation of excessive exercise performance is the ability to endure strenuous training without breakdown or maladaptation of the physiological systems. As training density increases, physical exhaustion can occur, particularly in the presence of inadequate rest and regeneration periods. When such disturbances occur, fatigue, overreaching (OR) and/or overtraining (OT) may occur. Additionally, it has been suggested that OT is, in certain terms, the result of disparity between load and load tolerance- this is of course different in different people.

This article introduces you to the definitions, prevalence, symptoms and diagnosis of overreaching and overtraining in endurance sports.

Prevalence of Overtraining

At higher levels of competition, the training load required for endurance-based sports can be as high as 20 hours per week. Whilst recreational strength and bodybuilding enthusiasts may well not train to a similar level, the output may be relative- but the outcome different. Chronic exposure to high volumes of exercise training/competition can result in high levels of energy expenditure on a regular basis resulting in athletes displaying specific symptoms of excess fatigue.

The prevalence of OT is thought to be highest in endurance-based sports requiring high volume, intense training, such as swimming, cycling, triathlon and to a lesser extent marathon running. For example, it has been suggested that over 65% of long distance runners will exhibit OT symptoms at some time in their competitive career, most likely due to the nature of the ‘anatomical adaptation’-based training cycles for each sport and the amount of recovery allowed between each training session. Whilst it is appreciated that OT may well occur in athletes across all levels of competition, it is more likely for a high level competitor to be exposed to such training cycles.


Definitions of Overtraining

Both OR and OT involve quantitative issues of training load balanced against qualitative issues of physiological and psychological stress, with the duration of recovery time and the persistence of symptoms being the main difference between the two classifications. For that reason it is difficult to agree a common definition that encompasses all types of sport. This has led to the following definitions:

Overreaching can be defined as:

“the accumulation of training and/or non-training stress resulting in short-term decrement in performance capacity with or without related physiological and psychological signs and symptoms in which restoration of performance capacity may take several days or weeks” [1].

Overtraining can be defined as:

“the accumulation of training and/or non-training stress resulting in long-term decrement in performance capacity with or without related physiological and psychological signs and symptoms in which restoration of performance capacity may take several weeks or months” [1].

With excessive training, and when the balance between training and recovery is not strictly monitored, OR and possibly OT are more likely to occur. This is the same ‘warning’ across all sports and all levels of client.

Whilst OR has qualitatively similar symptoms to OT it is more transitory and can be resolved with periods of rest and/or recovery. To a degree, a level of OR is required in fitter clients in order to promote adaptation- but of course then requires longer rest times to fully recover. Subsequently, OT has been described as a ‘long term’ form of overloading, whereas OR is simply short term OT.


Symptoms of Overtraining

There are a number of key symptoms that are consistently reported in those exhibiting OR/OT traits. These include symptoms of reduced sporting performance, increased feelings of physical fatigue and decreased maximum heart rate, as well as mental fatigue without associated physical fatigue, elevated basal metabolic rate, and loss of body weight.

OT can be partitioned into sympathetic (Basedowoid) or parasympathetic (Addisonoid) based on the prominence of autonomic nervous system (ANS) dysfunction. However a combination of both can exist over a longer timeline of OT. Basedowoid type OT symptoms include hyper-excitability and restlessness, whilst Addisonoid symptoms include high fatigue ratings, apathy, altered mood, and suppressed immune and reproductive function.

During early stage OT, the sympathetic system is continuously altered, however, during advanced OT, sympathetic activity is inhibited. Interestingly, sympathetic type symptoms are largely associated with explosive, anaerobic-type sports, whilst parasympathetic type is mostly associated with endurance sports.


Regardless of Addison or Basedow typing, identification of OR or OT can be complex since symptoms may be similar to those reported during routine training, making it difficult to disassociate them. It is therefore unlikely that such complex and diverse symptoms can be explained by a single mechanism.

Furthermore, whilst OT represents the most frequent and often feared dysfunction in athletes and gym-goers, there is no single objective parameter suitable for its identification. It is not surprising given the non-specific nature of the condition, that a myriad of physical, biochemical, psychological, musculoskeletal, haematological, cardiorespiratory and nutritional factors have been associated with the identification of both OR and OT. However, symptoms may be grouped into four main categories: psychological; physiological, biochemical and immunological.


  1. Halson, SL & Jeukendrup, AE. Does overtraining exist? An analysis of overreaching and overtraining research. Sports Med. 2004; 34(14): 967-81