Overtraining syndrome: a clinical review, Part 1

Excessive exercise leads to overtraining and a number of signs and symptoms.

Overload, in training terms, is when a body is exposed to a stress beyond that to which it is accustomed.¹  

Anyone who wants to enhance their physical performance must deal with the concept of overload.¹ Excessive overload of exercise can lead to overtraining and a number of signs and symptoms. Overtraining syndrome (OTS) occurs when athletes have a persistent imbalance between training and recovery, which can lead to fatigue and decreased performance.² The estimated lifetime prevalence among athletes having symptoms of overtraining is 7-20%, and between 30 and 100% of athletes report overtraining symptoms after intense training.³ OTS is distinguished by fatigue, mood disturbances and performance reductions, and has been projected to affect 20-60% of athletes in their careers.⁴ The estimated prevalence of OTS can vary widely between 15-60%, but it also depends on the type of sport and the training intensity and frequency.⁵ OTS is a specific and severe condition that can lead to performance decrements that last more than 2–3 months in addition to experiencing mood disturbances.⁶ Others suggested that athletes may never reach their prior performance magnitude again when suffering from OTS.⁷  

Overtraining syndrome is a result of progression from the state of overreaching that is defined as extended periods of performance impairment from having a prolonged imbalance between fatigue and recovery.⁸ Typically, overreaching occurs due to intensified training but is considered a normal outcome mainly from the short period recovery time (around two weeks).⁹ The entire spectrum of overtraining can be classified into three states: 1. functional overreaching, 2. non-functional overreaching and 3. overtraining syndrome. The first state is called functional overreaching (FOR), when there is a short-term performance decrease (days to few weeks) yet improvement in performance after recovery. The second level is considered non-functional overreaching (NFOR) and this occurs when performance worsens and lasts longer than FOR (weeks to months) before full recovery is seen in performance. This can lead to the third state called overtraining syndrome (OTS); this is when decreased performance is long-term (months to possibly indefinitely) and psychological symptoms are observed.¹⁰  

OTS is simply not well–understood. To demonstrate this lack of understanding historically the term unexplained underperformance syndrome (UPS) was devised. This term was created to include all athletes with persistent unexplained underperformance and consists of persistent unexplained performance deficit (recognized and agreed on by coach and athlete) despite two weeks of relative rest.¹¹ “Chronic fatigue,” “overreaching” and/or “staleness” are terms often referred to as overtraining syndrome.¹² Other terms in the early investigation of OTS were “overtraining syndrome,” “staleness,” “chronic fatigue in athletes” and “sports fatigue syndrome” have also been used.¹¹ 

General adaptation syndrome and the theories behind OTS

OTS, as a syndrome, and the continued training stress response has much to do with the general adaptation syndrome (GAS) established by Hans Selye in 1936.¹ The GAS syndrome is divided into three phases: 1. the alarm stage (when you’re taken off guard), 2. the resistance stage (when you try to maintain homeostasis) and 3. the exhaustion stage (when you fall victim to countering the stressor).¹³ The GAS is the framework practitioners and coaches can use for the periodization of training to control adaptation that follows along with the competition schedule for athletes.¹⁴ As a part of the stress response in the body, the term allostasis is appropriate here in the context of exercise and training. Allostasis is defined as an adaptive processes that attempts to maintain physiological homeostasis by producing chemical mediators such as epinephrine and cortisol.¹⁵  

The pathophysiology of OTS is complex and involves symptoms such as loss of energy for competition and libido, fluctuating emotions, increased anxiety and irritability, weight loss due to decreased appetite, excessive sweating and tachycardia.¹⁶ Due to the complexity of the pathophysiology and from the myriad of symptoms, several theories have been proposed. The most common theory of OTS is the glycogen hypothesis, which states that exercise-induced muscle glycogen depletion is correlated with a decrease in performance.⁸ The deficiency in glycogen can also result in decreased concentrations of branched chain amino acids (BCAAs) and an increase in oxidation.¹⁷ Another theory under consideration is the central fatigue hypothesis which states that tryptophan uptake can increase in the human brain and can lead to increased neurotransmitter serotonin (5-HT) levels and mood symptoms.¹⁷ Exercise decreases BCAA levels due to increased oxidation, which favors the entry for tryptophan in the brain and converts to 5-HT.¹⁷ Therefore, high intensity exercise can provoke alterations in amino acid metabolism and can trigger the cause of overreaching (OR) or OTS.¹⁸ A third theory is the glutamine hypothesis concludes that decreased glutamine levels can cause immune dysfunction and increases proneness to infection.¹⁷ Glutamine is essential for the functioning of immune cells.¹⁷ Glutamine decreases after prolonged exercise.¹⁷ Another hypothesis is associated with oxidative stress and states that oxidative stress resting markers increase with exercise and are higher in over-trained athletes.¹⁷ Some reactive oxygen species are regulated for cellular repair when released from damaged muscles.¹⁷ However, reactive oxygen species (ROS) can cause muscle fatigue, inflammation and soreness with a declined athletic performance when oxidative stress turns pathologic.¹⁷ Another theory shows promise as far as potential biomarkers are concerned is the cytokine hypothesis. The cytokine hypothesis states cytokines are released and activated by the inflammation of several cells and tissue microtrauma during OR and OT.¹⁹ Cytokines are a group of chemical messengers released into the bloodstream when responding to infection, tissue injury and biomarkers of stress.¹⁹ Inflammatory cytokines may be the cause of psychological and behavioral changes in overtraining syndrome.³ The proinflammatory cytokines, interleukin 1-beta (IL-1β) and tumor necrosis factor-alpha (TNF-α) could interfere with the brain, leading it to symptoms of OTS.³ This symptomology can lead to sleep disturbance, depression and a decrease in appetite.³ 

Conclusion

This article introduces the concept of OTS from a historical standpoint and the main physiological theories. Although the research focuses on those of an elite athletic status, it can occur to those who exercise of all ages and conditions. This research brief did not consider such things as burnout, overuse injury and tapering. The concept of OTS and its multitude of potential theories as part of the overall equation should be considered. While most focus on the actual training of those involved in exercise and athletics, the clinical aspects of the recovery process require further attention to fully grasp OTS.  

NAVY SMITH, BS, is currently a Master’s of Athletic Training student at the University of Alabama in Tuscaloosa, Ala. She can be reached at navy.o.smith@students.cookman.edu. This clinical review is based on Smith’s senior research thesis at Bethune-Cookman University.  

TIMOTHY MIRTZ, DC, PHD, is an associate professor and chair of the Department of Secondary and Physical Education at Bethune-Cookman University in Daytona Beach, Fla. He can be reached at mirtzt@cookman.edu. 

TORRANCE WILLIAMS, DHSC, ATC, LAT, is an associate professor and chair of the Department of Rehabilitation Sciences and program director for athletic training education at Bethune-Cookman University in Daytona Beach, Fla., and can be reached at williamsto@cookman.edu.  

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