Overtraining syndrome in athletes

INTRODUCTION — Many athletes undertake high training volumes in a bid to enhance performance. The consequences of training at such high intensity and duration may include fatigue, illness, and injury. Incorporating appropriate rest and recovery (including sleep) into a training program is essential to ensure a balance between training and recovery and to minimize the potential negative effects of training.

Overtraining syndrome (OTS) is a complex clinical disorder identified in the athletic population that represents a maladaptive response to training. While many studies have focused on endurance sports, OTS has also been described in sports that rely on power and anaerobic performance. In addition, it is reasonable to assume that members of occupations requiring intensive physical training in combination with other biologic, psychologic, and social stressors (eg, firemen, police officers, military personnel) may suffer from OTS. A term frequently associated with OTS is "burnout." While burnout may develop in athletes, it is also found in numerous occupations, including health care providers. OTS is thought to be the result of an imbalance between training and recovery, while burnout is secondary to mental overload.

The etiology, epidemiology, presentation, and management of OTS will be discussed here. Specific injuries that may be sustained as a result of overtraining are reviewed in the topics devoted to those injuries.

DEFINITIONS AND PRINCIPLES OF ATHLETIC TRAINING — In order to understand overtraining, one must first understand the basic terminology and principles of training. The key principles of athletic training generally are discussed below; the principles of strength training are discussed in greater detail separately. (See "Physical activity and strength training in children and adolescents: An overview" and "Strength training for health in adults: Terminology, principles, benefits, and risks" and "Practical guidelines for implementing a strength training program for adults".)

Athletic training can be defined as specific, repeated body movements performed according to a planned program in order to improve or maintain one or more elements of physical fitness (eg, speed, endurance, strength, power). Intense athletic training is intended to disrupt the body's homeostasis, temporarily causing neuromuscular fatigue. Immediately following such a stress, performance declines, but given adequate rest and nutrition, the body regenerates and re-establishes homeostasis at a new level better able to cope with the activity that initially disrupted homeostasis. Once the body adapts, the previous training stress is no longer capable of disrupting homeostasis and stimulating further adaptation. Further progress requires additional stress. This is known as the overload principle, and the body's response to such training is referred to as overcompensation or super-compensation.

Progressive overload is the planned use of increases in training intensity or volume to stimulate successive adaptations and thereby create long-term improvements in a specific component or components of physical fitness and performance. To maximize the benefits of training using the overload principle, subsequent training sessions involving overload should not be performed until recovery is complete. However, depending upon the activity, the point when recovery is complete may not be easily identified. Intense training creates the largest stress and elicits the greatest training effect, but in most cases, it also has the largest potential to cause injury and disrupt normal physiologic processes.

Additional principles that form the basis for athletic training programs include the following:

●Adaptation is the change in physiologic functions that occurs in response to training, with sufficient rest and recovery.

●Individualization refers to the individual nature of training gains. Such gains vary with each athlete's rate of adaptation, which is influenced by the type and volume of training stimulus, lifestyle habits (eg, nutrition, sleep), genetics, age, sex, and any medical conditions.

●Maintenance refers to sustaining achieved training gains.

●Reversibility refers to the loss of performance gains that occurs when training stops (also called detraining). Only one or two weeks of detraining can significantly reduce endurance and cardiovascular fitness gains, and many training improvements can be lost completely after several months.

●Specificity means that the body adapts in precise ways to a specific type, volume, and intensity of training load and the primary energy system(s) engaged during training.

Although training schedules vary, all training involves placing greater stresses on the body as it adapts to prior training loads in order to induce further improvements in performance. Occasionally, coaches and athletes incorporate a sequence of brief, planned periods of greatly increased training load with little time for regeneration. It is thought that when the athlete resumes a less rigorous training schedule (taper period) following such an increased period of loading, this ultimately leads to larger overall gains in performance. The type of training sequence that intersperses periods of increased training intensity with periods of lower intensity (or cross-training) to allow adequate recovery is called periodization. Periodization can not only increase optimal performance, but decrease the risk of overtraining syndrome (OTS). A more detailed description and review of periodization, recovery, nutrition, psychology, and skill acquisition in individual and team-sport athletes can be found in the following reference [1].

Recovery is an essential part of athletic training. Researchers describe three major processes involved in recovery from training [2,3]:

●Hydration and nutrition

●Sleep and rest

●Relaxation and mental recovery

A detailed discussion of recovery methods is beyond the scope of this topic, but a brief summary is necessary for understanding overtraining. Virtually all clinicians feel that adequate hydration, nutrition, rest, and sleep are key factors in the recovery process [3-9]. In addition, anecdotal information suggests that for many athletes' mental recovery, emotional support, stretching, and massage may speed recovery from intense training.

The primary goals of nutrition and rehydration during recovery from intense training or competition are to replenish fluid and glycogen stores and facilitate muscle repair [4,10,11]. Following such activity, we suggest athletes do the following:

●Replace 150 percent of fluid losses over six hours

●Consume 1.2 g of carbohydrate/kg body weight each hour for six hours

●Consume 10 to 20 g of protein during first hour

Endurance and team-sport athletes should replace approximately 150 percent of their fluid loss (as determined by the difference between pre- and post-exercise bodyweight measurements) over the first six hours following training [12]. To replace glycogen stores, such athletes should consume approximately 1.2 g of carbohydrate per kg of body weight (g/kg) every hour for the first six hours. This can be difficult, but ensuring protein intake of 0.2 to 0.4 g/kg per hour reduces carbohydrate requirements to 0.8 g/kg per hour [4].

Adequate intake of protein and other nutrients is essential for muscle recovery. General recommendations for maintaining lean muscle mass include consuming 10 to 20 g of quality protein within the first hour following any intense training and consuming approximately 1.5 to 2 g/kg per day of quality protein during extended periods of athletic training. Of course, an individual athlete's nutritional requirements can vary substantially depending upon the sport, intensity of training, age, and other factors.

TERMINOLOGY OF OVERTRAINING — Overtraining is thought to represent a range of responses and disorders that exist along a continuum [13-15]. The presenting symptoms of these disorders overlap substantially, with time to recovery being the main variable [5]. The following terminology is widely used to describe these disorders:

●Acute fatigue (AF) – AF is the immediate result of overload training. Although fatigued, the athlete experiences no perceivable decline in performance.

●Functional overreaching (FOR) – Overreaching is broadly defined as a short-term decrement in athletic performance after a period of overload training. FOR is a short-term (less than two weeks), training-induced increase in fatigue and decline in performance that is transient and associated with increased training loads. It should be noted that FOR is often an integral part of an elite athlete's training program and, when used correctly, can improve performance.

●Nonfunctional overreaching (NFOR) – NFOR is defined as intense overload training that leads to a longer period of decreased performance than FOR (typically two weeks to two months), but adequate rest leads to a full recovery. NFOR is frequently accompanied by increased psychological and/or neuroendocrine symptoms of the type associated with overtraining, whereas FOR is usually not.

●Overtraining syndrome (OTS) – OTS (also referred to as "staleness" or "burnout") is defined as a prolonged (usually greater than two months) decline in sport-specific performance. Common symptoms and signs associated with OTS include premature fatigability, emotional lability, lack of motivation, overuse injuries, and infections (most commonly respiratory infections). Recovery is variable, and many months may be needed before the athlete returns to their baseline training capacity.

EPIDEMIOLOGY — The precise incidence of OTS is not known. Studies of overtraining syndrome (OTS) are limited by variations in diagnostic criteria and small sample sizes, along with various methodologic issues. One early study reported that 65 percent of elite competitive swimmers had experienced staleness at some time in their career [16]. A subsequent survey study of endurance runners describes a prevalence rate of 10 percent during one training cycle [17] and a lifetime risk of 64 and 60 percent among male and female runners, respectively [18,19]. Athletes who have experienced OTS appear more likely to relapse. As an example, a study of college swimmers reported that 91 percent of those experiencing OTS in their freshman year suffered a repeat episode during the subsequent year, as opposed to 34 percent of those who did not experience an initial episode [20].

Data on overtraining in elite young athletes is limited. An incidence of 20 to 30 percent has been reported among high-level athletes, with higher rates among individual-sport athletes, females, and more elite competitors [21]. However, OTS is not exclusive to elite athletes [22]. Recreational youth athletes may not exercise with the same intensity and frequency as elite youth athletes, but they encounter other stressors that contribute to OTS, such as scheduling difficulties, conflicts with their schoolwork or job, and a lack of coaching.

CURRENT THEORIES AND PHYSIOLOGY — No single theory explains the etiology of overtraining syndrome (OTS). Commonly cited theories include autonomic imbalance, glycogen depletion, low energy availability-relative energy deficiency in sport [23], branched-chain amino acid (BCAA) hypothesis, central fatigue, and cytokine hypothesis [24]. These pathophysiologic models stem from observations of the biochemical and neuroendocrine changes associated with overload training. Investigation of these hypotheses is ongoing but difficult, as small study populations, lack of standardized definitions, and confounding variables hamper progress. OTS is likely multifactorial, involving some aspects of all the theories described below.

●Autonomic imbalance ‒ The autonomic imbalance hypothesis proposes that underlying imbalances in the autonomic nervous system cause OTS [6,25]. The initial stage of this proposed mechanism involves negative feedback caused by a surge of catecholamine release during periods of heavy training. This causes a decrease in baseline catecholamine secretion. Second, an increase in metabolism during exercise causes an imbalance among plasma amino acids and alterations in brain neurotransmitter metabolism, leading to an increase in the concentrations of aromatic amino acids (phenylalanine, tryptophan, and tyrosine). The resulting increases in hypothalamic tryptophan and cerebral dopamine concentrations cause "metabolic error signals" with inhibitory effects on the sympathetic nervous system. In addition, the increase in core temperature associated with high-intensity training may exert an inhibitory effect on the sympathetic centers of the hypothalamus. Third, there is a neuronal negative feedback system that results in catecholamine receptor down-regulation in the exercising muscles.

●Glycogen depletion ‒ The glycogen depletion hypothesis suggests that with extensive periods of heavy training, glycogen depletion ensues in muscles. Glycogen is the primary source of energy for moderate to intense exercise [26], and low levels of muscle glycogen can cause muscular (peripheral) fatigue and a decline in performance. In addition, low levels of glycogen trigger increased oxidation of BCAAs to glucose in an attempt to supplement deficient energy supplies. This lowers the body's total pool of the BCAAs (leucine, isoleucine, and valine) and can produce central fatigue [27].

●Low energy availability-relative energy deficiency – High training loads combined with inadequate energy intake are common among athletes who participate in sports that require high power-to-body weight ratios (eg, Olympic-style weightlifting, wrestling). Such prolonged, inadequate energy intake may result in relative energy deficiency in sport (RED-S), a condition that shares many symptoms with OTS [23]. The similarities between OTS and RED-S have been highlighted and suggest that their underlying etiology may be similar.

●Central fatigue ‒ The central fatigue theory hypothesizes that OTS is caused by an increase in the synthesis of the neurotransmitter 5-hydroxytryptamine (5-HT) in the central nervous system (CNS) [6,24,28,29]. With extensive exercise, glycogen levels become depleted in muscles, leading to the use of secondary energy sources by the muscles. The BCAAs (leucine, isoleucine, and valine) are oxidized to glucose. Concurrently, an increase in the level of fatty acids occurs. The fatty acids compete with tryptophan for albumin binding sites, leading to an increase in plasma tryptophan. As both the BCAAs and tryptophan use the same transporter to pass through the blood-brain barrier, a decrease in plasma BCAA and an increase in plasma tryptophan lead to an increase in tryptophan passing through into the CNS. In the brain, tryptophan is converted into 5-HT. 5-HT is well known to play a role in various neuroendocrine and emotional functions, all of which can be seen with OTS. This connection between OTS and an increase in the free tryptophan to BCAA ratio forms the basis for the BCAA hypothesis.

●Cytokine hypothesis ‒ The cytokine hypothesis states that incomplete recovery of locally damaged tissue causes a local inflammatory response that becomes systemic, producing elevated levels of proinflammatory cytokines IL-1 beta, TNF-alpha, and IL-6. Persistent elevations of these cytokines induce CNS and peripheral fatigue as well as hormonal and metabolic changes [6,30].

●Disturbed sleep ‒ Sleep is essential for optimal physiological and psychological recovery. Several observational studies report that sleep is disturbed by significant increases in training load [31]. Whether poor sleep is a contributor to or consequence of OTS remains to be elucidated; however, large numbers of athletes report poor sleep during intensified training [32,33]. This may be due to inadequate recovery time between training sessions, timing of training sessions (early morning or late evening), or travel stress and jet lag. (See "Evaluation and diagnosis of insomnia in adults" and "Insufficient sleep: Evaluation and management".)

CLINICAL PRESENTATION — Common signs and symptoms associated with overtraining are summarized in the following table (table 1). Researchers have described four major categories of symptoms and signs associated with overtraining: physiological, psychological, biochemical, and immunological [6,15,20,34]; the last two categories are typically not helpful clinically and are discussed further below. (See 'Biochemical markers of overtraining' below.)

Subjective complaints of overtrained athletes may include fatigue, persistent muscle soreness, lack of motivation or competitive spirit, extreme sleepiness, depression, irritability, lack of cooperation with teammates or coaching staff, and difficulty concentrating. Athletes often report feeling that greater effort is required to perform during training or competition. Typically, there is a history of intense, high-volume training followed by a persistent decline in performance, but in all cases, performance has declined. This high-intensity, high-volume training is often coupled with reduced recovery (increased stress and/or poor sleep). Often, the athlete has already experimented with coaching changes or increased or changed their training regimen due to a drop in performance, often out of a mistaken belief that they are undertraining. The physical examination is often normal, but the examiner may note an elevated heart rate or blood pressure. Such findings are particularly notable in endurance athletes or athletes who perform a significant amount of endurance-type training (eg, participants in most team or field sports) and would normally have a low resting heart rate. Other physical findings may include chronic or recurrent overuse injuries, anorexia, weight loss, and signs of respiratory infection (due to increased susceptibility).

DIAGNOSTIC EVALUATION — There are no widely accepted guidelines for establishing the diagnosis of overtraining syndrome (OTS). Evaluation of the fatigued athlete often requires several clinic visits during which the clinician carefully considers the differential diagnosis [5,6,20,24,35-38]. (See 'Differential diagnosis' below.)

Initial clinic visit — At the first visit, the clinician obtains a thorough history focusing on the chief complaint, training program, sleep, life stressors, diet, medications, and recent or chronic illness, and conducts a thorough review of systems (ROS). The goals and implementation of the athlete's training program are reviewed in detail. It is important to ask about any recent increase in the frequency, duration, or intensity of training prior to the onset of symptoms. In many cases, an athlete has recently increased their training schedule in preparation for an upcoming competition. Common symptoms and signs associated with OTS are summarized in the accompanying table (table 1).

Given the standard differential diagnosis, a sensible initial laboratory evaluation includes a complete blood count, serum or plasma ferritin concentration, basic metabolic panel (including serum sodium, chloride, potassium, and bicarbonate; and creatinine and blood urea nitrogen [BUN]), and thyroid-stimulating hormone (TSH). Other laboratory studies may be indicated based upon the history, but extensive testing is usually not required. As examples, we obtain a heterophile antibody test (eg, "Monospot" test) if the history suggests possible infectious mononucleosis and an electrocardiogram if an endurance athlete has a significantly elevated resting heart rate.

If OTS is suspected on the basis of the initial evaluation, we suggest that the athlete substantially decrease the intensity of their training. Generally speaking, complete rest is not advised as this may cause both detraining and an increase in psychological stress. During that time, athletes may participate in some type of light (ie, non-strenuous) recreational exercise to maintain a base level of fitness while the workup is performed. For some athletes, general recommendations to "slow down" may not be sufficient. In such cases, the clinician can give a prescription of no more than 30 minutes per day of light aerobic exercise using an elliptical trainer or bicycle, or swimming at an easy level (approximately no more than 65 to 70 percent of the maximum heart rate), and weight workouts no more frequently than every other day including no more than five exercises of two sets of 12 to 15 repetitions with light weights (approximately no more than 40 to 50 percent of the one repetition maximum).

The clinician should ask the athlete to compile a three-day food diary between visits, which can be reviewed at the follow-up visit. Everything the athlete eats and drinks over the three days should be recorded in the diary. Often, nutritional deficiencies cause declines in performance, and evaluation by a sports nutritionist may be valuable after the first visit. (See "Dietary assessment in adults", section on 'Food diary'.)

Follow-up — At the first follow-up visit (usually two to three weeks after the initial evaluation), the clinician should review the patient's symptoms and any laboratory results and inquire about training over the past two to three weeks. Specific laboratory abnormalities should be addressed as indicated. The clinician and patient should review the three-day food diary, and dietary adjustments or supplementation should be made as needed. Repeating the history is often useful as athletes may recall or be more forthcoming about events that have contributed to their fatigue. If symptoms have improved, the athlete may be suffering from physiologic fatigue (acute fatigue or functional overreaching) and may be able to return to training with reductions in the volume or intensity of the training schedule. The athlete may continue cross-training activities (ie, physical activity that emphasizes different muscle groups and at a lower intensity than the sport-specific activity) and appropriate management of other identified stressors. As such athletes gradually return to training, it is important to monitor subjective signs of overtraining, such as perceived effort, and objective signs, such as decrements in performance. Definitions and principles related to training, fatigue, and overtraining are provided above. (See 'Definitions and principles of athletic training' above and 'Terminology of overtraining' above and 'Suggested approach to monitoring' below.)

If there is no improvement, the athlete may be suffering from pathologic fatigue (nonfunctional overreaching [NFOR] or OTS). Such patients require prolonged relative rest, avoidance of intense training, and further work-up as indicated by the history, examination, and testing results to assess alternative diagnoses. Consultation with a dietician and sports psychologist is advisable. (See 'Differential diagnosis' below and 'Treatment' below.)

Evaluation of the athlete with symptoms or signs consistent with OTS is difficult, in part because the spectrum of possible symptoms is vast. Sport-specific parameters of dysfunction, such as increased running times for a specific distance event or decreased weightlifting totals, may provide insight. However, there is no single performance measurement or laboratory study that can be used to diagnose OTS. Thus, careful evaluation and investigation of other possible diagnoses is an important part of the workup. (See 'Diagnosis' below and 'Differential diagnosis' below.)

Preliminary research suggests that a diminished serum lactate concentration following performance testing is a consistent finding in overtrained athletes [3,39]. However, lactate studies are often limited by the availability of prior baseline data. One study reported on diagnosing OTS in athletes using a two-bout exercise test protocol [40]. Researchers studied a group of 10 underperforming athletes, five of whom were ultimately diagnosed with OTS and five with NFOR. After performing the two-bout maximal exercise protocol (two maximal exercise tests separated by four hours), the athletes with OTS had reduced maximal lactate concentrations, defined as concentrations ≤8 mmol/L, and higher serum prolactin and adrenocorticotropic hormone (ACTH) concentrations. This two-bout exercise protocol may be a useful test for diagnosing OTS, but further study is required. A systematic review of hormonal aspects of OTS concluded that baseline hormone levels are not a good predictor of OTS; however, blunted ACTH and growth hormone responses to stimulation tests may be good predictors for OTS [41].

Additional follow-up visits are scheduled as needed based upon the initial workup. As a rule of thumb, athletes with a preliminary diagnosis of OTS are seen every four weeks for reassessment. If there are any concerns about the athlete's nutrition, evaluation by a sports nutritionist is recommended. Consultation with a sports psychologist is often helpful if treatment requires prolonged restriction from sport and an increase in life stressors precipitated the decline in performance. An assessment of sleep, via questionnaire and diary, or a consultation with a sleep specialist may also be recommended if the individual complains of poor sleep quality or quantity. (See 'Sleep disorder' below and "Evaluation and diagnosis of insomnia in adults" and "Insufficient sleep: Evaluation and management".)

DIAGNOSIS — The diagnosis of overtraining syndrome (OTS) is one of exclusion, and is made over the course of two or three clinic visits and reassessments. Careful evaluation and investigation of other possible diagnoses helps to reassure the athlete and clinician about a diagnosis of OTS and ensure athlete compliance with the prescription for rest. Key aspects of the history include a period of intense, high-volume training followed by a persistent decline in performance. The review of systems may note sleep disturbance, irritability, weight loss, asthenia, a sensation of heavy legs, and myalgia with low-level exercise. The laboratory evaluation is typically unremarkable. Lack of improvement despite full rest during the two- or three-week period of reassessment helps to confirm the diagnosis.

DIFFERENTIAL DIAGNOSIS — Overtraining syndrome (OTS) is both a clinical diagnosis and a diagnosis of exclusion. The differential diagnosis is extensive and includes all the possible causes of fatigue. The differential diagnosis of fatigue is reviewed in detail separately (table 2); alternative diagnoses of particular relevance to OTS are discussed below. (See "Approach to the adult patient with fatigue".)

Sleep disorder — Inadequate quality and quantity of sleep may contribute to increased fatigue, poor performance, and alterations in mood [42-46]. If a medical sleep disorder such as obstructive sleep apnea (OSA) or restless leg syndrome (RLS) is suspected, referral to a sleep specialist is warranted. The Athlete Sleep Behavior Questionnaire may be used to gain an understanding of behaviors that contribute to sleep disturbance [47]. Other clinical questionnaires such as the Pittsburgh Sleep Quality Index may be used to determine if the athlete is a "good" or "bad" sleeper using a series of subjective questions about the individual's sleep during the previous month [48]. (See "Evaluation and diagnosis of insomnia in adults" and "Insufficient sleep: Evaluation and management".)

Nutritional deficiency — Multiple observational studies report inadequate energy intake among elite athletes [49]. As an example, a study of the food preferences and energy intake of elite male and female figure skaters reported that total energy intake and consumption of vitamins E and D, magnesium, and potassium were only two-thirds of that recommended [50].

Diagnostic clues to potential nutritional deficiencies include a history of attempting to lose weight while training and lack of oversight from a dietician. Reviewing an athlete's food diary, as well as the assistance of a sports nutritionist, can provide insight. Up to several months may be needed before improvements in performance are noted following correction of a nutritional deficiency. As an example, correcting iron deficiency anemia may take up to three months. In addition, correcting a nutritional deficit does not necessarily obviate the need for implementing training reductions as nutritional problems and overtraining can coexist. A brief discussion of proper nutrition for recovery from athletic training is found above. (See 'Definitions and principles of athletic training' above.)

Low energy availability-relative energy deficiency — OTS and relative energy deficiency in sport (RED-S) share similar symptoms and diagnostic challenges. In practice, low energy availability that causes RED-S may incorrectly be diagnosed as OTS [23]. Like OTS, RED-S is a diagnosis of exclusion. It is most common among athletes who participate in sports that require high power-to-body weight ratios (eg, Olympic-style weightlifting, wrestling).

Anemia and iron deficiency — Iron deficiency can exist with or without anemia. Although anemia from occult blood loss can develop in athletes and non-athletes alike, iron deficiency in young athletes is usually related to inadequate iron intake. The condition is more common in female athletes but can occur in males. Fatigue with mild iron deficiency or mild anemia generally develops only with exertion and athletes feel fine when at rest. Anemia is easily diagnosed by measuring a serum hemoglobin concentration, while a serum or plasma ferritin is used to diagnose iron deficiency. The initial evaluation and management of iron deficiency without anemia in athletes are much the same as with mild to moderate iron deficiency anemia and are reviewed separately. (See "Causes and diagnosis of iron deficiency and iron deficiency anemia in adults" and "Iron requirements and iron deficiency in adolescents" and "Treatment of iron deficiency anemia in adults".)

Psychological disorder — Mood disorders are common in all age groups and it can be difficult in some cases to distinguish psychological problems such as depression from overtraining. Athletes are exposed to many stressors related (eg, overtraining) and unrelated to sport. However, data suggest that the prevalence of mental health disorders among athletes is comparable to the general population [51]. Diagnostic clues include fatigue on awakening (ie, not improved with rest), general apathy, and disinterest in activities the athlete typically enjoys. The differential diagnosis of depression is reviewed in greater detail separately. (See "Unipolar minor depression in adults: Epidemiology, clinical presentation, and diagnosis", section on 'Differential diagnosis' and "Pediatric unipolar depression: Epidemiology, clinical features, assessment, and diagnosis".)

Burnout may occur following years of training and competition. There is an overlap of symptoms with depression and thyroid dysfunction. The principal distinction between burnout and overtraining is impaired mental performance versus impaired physical athletic performance.

Performance anxiety can manifest as fatigue. Often, such anxiety is associated with competition rather than practice or training, during which fatigue is not evident. This helps to distinguish anxiety from overtraining, which affects both training and competition.

Medical conditions — The presentation of a number of medical conditions can mimic that of OTS (table 2). Notable among these conditions are hypothyroidism, cardiomyopathy, and infectious mononucleosis.

Thyroid disorders — Thyroid disease is a relatively common cause of fatigue and malaise, including among athletes. Hypothyroidism in particular may be mistaken for OTS as both produce fatigue and depression. However, hypothyroidism causes a number of additional signs and symptoms not typically associated with OTS, including cold intolerance, weight gain, constipation, slow movement and speech, delayed relaxation of deep tendon reflexes, coarse skin, and periorbital edema. A normal thyroid-stimulating hormone (TSH) serum concentration essentially rules out hypothyroidism, but TSH concentrations may be low in athletes with OTS secondary to the physiologic stress being placed on the overtrained athlete, and additional testing may be needed. The approach to such testing is described separately. (See "Clinical manifestations of hypothyroidism" and "Diagnosis of and screening for hypothyroidism in nonpregnant adults".)

Less commonly, hyperthyroidism is mistaken for OTS, as both may cause fatigue, agitation, and a relative tachycardia. However, hyperthyroidism can usually be distinguished on clinical grounds as it causes numerous other distinctive signs and symptoms, including heat intolerance, warm skin, weight loss, increased frequency of bowel movements, urinary frequency, stare and lid lag (exophthalmos), and possibly a palpable goiter. (See "Overview of the clinical manifestations of hyperthyroidism in adults" and "Diagnosis of hyperthyroidism".)

Cardiomyopathy and myocarditis — Many patients with hypertrophic cardiomyopathy (HCM) have no or only minor symptoms; thus, affected individuals are often diagnosed only as a result of family screening, detection of a murmur during routine examination, or identification of an abnormal ECG. Of the symptomatic patients with HCM, some may experience exercise intolerance and fatigue, which may be confused with OTS. A few athletes with HCM may present with near-syncope or syncope, inappropriate levels of fatigue when following an appropriate training program, palpitations, or exertional chest pain. There may be a family history of cardiomyopathy or unexplained sudden death in young relatives. Athletes in whom cardiomyopathy is being considered should refrain from strenuous activity pending assessment by a cardiologist, including an echocardiogram. (See "Hypertrophic cardiomyopathy: Clinical manifestations, diagnosis, and evaluation".)

Athletes with myocarditis may have symptoms and signs of heart failure, including peripheral or pulmonary edema, exertional dyspnea, with or without chest pain, and a history of a viral syndrome within the prior six weeks. (See "Clinical manifestations and diagnosis of myocarditis in adults".)

Post-viral syndrome and infectious mononucleosis — Patients with a post-viral syndrome or infectious mononucleosis may report the sudden onset of symptoms suggestive of a viral infection approximately 2 to 12 weeks prior to the onset of fatigue. The viral prodrome may have manifested as fever, lymphadenopathy, myalgias, sore throat, cough, and/or rash. In some cases, these symptoms may have been quite minor, such that the athlete does not associate existing fatigue with the prior illness. (See "Infectious mononucleosis".)

Other conditions — A number of other medical conditions are less frequently confused with OTS but may present with findings consistent with overtraining, and the clinician should be aware of them when assessing the fatigued athlete. These include the following:

●Medication side effects (eg, antidepressant, anxiolytic, beta blocker)

●Substance abuse

●Postconcussive syndrome (see "Postconcussion syndrome")

●Eating disorders (see "Eating disorders: Overview of epidemiology, clinical features, and diagnosis")

●Environmental allergies

●Infection

●Pregnancy

●Diabetes mellitus (see "Epidemiology, presentation, and diagnosis of type 1 diabetes mellitus in children and adolescents" and "Epidemiology, presentation, and diagnosis of type 2 diabetes mellitus in children and adolescents")

●Malignancy

●Congenital or acquired heart disease [52]

TREATMENT — Just as the etiology of overtraining syndrome (OTS) is not fully understood, so too is the optimal approach to management. Treatment of OTS is based to a large extent on clinical experience and intuition. It is important to realize that there is no "quick fix" for OTS. Ultimately, rest may be curative. However, early intervention in athletes with nonfunctional overreaching (NFOR) can help avoid the need for a protracted recovery from OTS.

If an athlete experiences signs of fatigue and declining performance, merely decreasing the training intensity by 50 to 75 percent for one to two weeks may result in improved performance in training and competition. If symptoms are more severe, of longer duration, or have failed to respond to decreased training intensity, more significant restrictions are likely to be needed, including significant reduction in all high-intensity training and the number of training sessions per week, with only light exercise prescribed. Guidelines for light exercise are described above. (See 'Diagnostic evaluation' above.)

Often, clinicians find it difficult to convince athletes with NFOR or OTS to rest. Therefore, at the start of any proposed rest period, it is important to educate the athlete in order to achieve compliance with reductions in training and to prevent recurrence. Take time to explain to the athlete the beneficial effects of rest and recovery upon performance and adaptations to training, and that inadequate rest and poor recovery are likely significant factors contributing to their current fatigue and poor performance. With adult athletes, it may be helpful to share position statements and guidelines about overtraining from professional societies, such as the American Medical Society for Sports Medicine [5,15,53].

When looking for possible sources of emotional stress, careful review of the athlete's diet and sleep schedule is just as important as a review of training and competition schedules. Early consultation with a dietician and psychologist can be beneficial. Continual surveillance for signs and symptoms of other causes of fatigue is important.

Once an athlete has been diagnosed with OTS, decisions about treatment and plans for return to activity are best made as a multidisciplinary team that includes the primary clinician managing care and any consulting specialists, athletic trainers, and coaches involved with the patient. Close communication among this team is important. Further, including the athlete in the decision-making process with this team may be important to ensure compliance with training modifications. Questions regarding when and how the athlete should resume training can be difficult. A specific plan to assess progress and avoid relapse should be in place and should include consistent monitoring, such as periodic time trials and psychological assessments. (See 'Suggested approach to monitoring' below.)

Training for athletes recovering from OTS should be advanced gradually and sequentially. Initially, the athlete should concentrate on gradually increasing the frequency of training, followed by the duration of each training session, and finally the intensity of training sessions. Abrupt increases in training volume or intensity must be avoided. An athlete's return to full training and competition should not proceed until the physiological and psychological symptoms and signs associated with the development of OTS have resolved and the athlete's performance (eg, time trial) or training quality is approaching that achieved prior to the diagnosis of OTS. Upon return to full training and competition, the athlete should pay careful attention to their sleep, nutrition, school and/or workloads, and competition-related stress.

PREVENTION AND MONITORING — A great deal of research has been performed looking for signs or tests that accurately predict when an athlete is at risk of overtraining. Despite common acknowledgement that monitoring athletes for overtraining is important, no single reliable indicator of overtraining syndrome (OTS) has been identified.

The importance of monitoring the effects of intense overload training was demonstrated in a prospective study of 33 trained triathletes [54]. In this study, athletes were divided into two groups. One group (n = 10) performed baseline training for two sequential three-week periods, while the test group (n = 23) was exposed to one three-week period of overload training. Eleven of the triathletes in the overload group were diagnosed with functional overreaching (FOR) on the basis of decreased performance and high perceived fatigue. The remaining 12 athletes in the overload group were diagnosed with acute fatigue (AF). During the four-week taper that followed training, the AF group experienced a super-compensation response leading to improved performance, whereas the FOR group showed a decline in performance and the control group had no change.

Particularly given the absence of reliable markers for diagnosing OTS, prevention remains the cornerstone of management. Well-designed training schedules that incorporate the concepts of periodization and cross-training, as well as adequate rest and minimization of life stressors, are employed to prevent OTS. To reduce individual risk, coaches and trainers also rely on their experience and intuition when determining the optimal training intensity and volume for their athletes. While guidelines for appropriate training intensity and volume vary widely, limited evidence in elite swimmers and others suggests that using programs involving higher intensity and reduced volume may aid recovery and potentially reduce the risk of OTS [55].

A range of monitoring devices and tools have been developed to quantify training loads (eg, power output, time-motion analysis) and physiologic responses (eg, oxygen uptake, heart rate, blood lactate) in athletes. However, high quality evidence supporting the application of such tools is generally lacking, and no single tool can be relied upon to determine whether an athlete is at risk for overtraining [53]. (See 'Psychological and recovery monitoring' below and 'Physiologic markers of overtraining' below and 'Biochemical markers of overtraining' below.)

Prevention measures — Several steps can be taken to reduce the risk of OTS, including ensuring adequate sleep and recovery, proper nutrition, and appropriate training programs. Adequate sleep (eg, minimum of eight hours nightly for most athletes) improves performance and may reduce the risk of overtraining [42,56]. Proper nutrition can mitigate the stress response to acute exercise. Conversely, glycogen depletion causes an increase in catecholamine and cortisol concentrations [39]. Supplemental carbohydrate intake during overload training can blunt such elevations in cortisol and attenuate perceived exertion [57]. A review of the nutritional needs of athletes is beyond the scope of this topic, but basic guidelines for carbohydrate intake and the intake of other nutrients for athletes are provided above. (See 'Definitions and principles of athletic training' above.)

Periodization is the planned organization of training loads to allow adequate recovery. Appropriate use of periodization is one important strategy for reducing the risk of OTS. Periodization may be performed over the short and long term. Short-term strategies might include one day off in seven and alternating hard and easy days. Longer-term periodization might include one week of reduced training every 8 to 12 weeks or one month of light or minimal training each year.

Suggested approach to monitoring — Due to the limited accuracy of individual psychological and physiological markers of overtraining, many experts believe that using a combination of techniques is the best way to assess for signs of developing OTS [53]. The author's preferred combination of monitoring tools includes regular (eg, weekly) measurement of training volume and well-being (including muscle soreness, stress, sleep) and regular use of a formal psychological assessment tool (Total Quality Recovery [TQR] or the Recovery Stress Questionnaire [REST-Q], described below). In addition, serial sport-specific performance trials, as applicable, can provide the athlete, coach, and clinician with early signs of overtraining.

Many athletes keep daily training logs, which include training details (type of training, time, distance, intensity) and assessments of individual well-being, life stresses, and any symptoms of stress (eg, fatigue, depression, irritability). Soreness, injuries, and illnesses are also included.

Psychological and recovery monitoring — Some of the earliest changes noted in patients with OTS are psychological. In addition, multiple observational studies suggest that mood disturbances increase in frequency with increased training loads and return to baseline after loads are reduced [58].

Numerous questionnaires and assessments have been used to identify the early psychological changes of patients at risk for OTS [3]. The Profile of Mood States (POMS) is one such psychological assessment tool for overtraining [59]. The POMS consists of 65 items and yields a global measurement of affect or mood based on assessments of tension/anxiety, depression/dejection, anger/hostility, vigor/activity, fatigue/inertia, and confusion/bewilderment. The patient responds on a five-point scale to 65 adjectives describing feelings and moods experienced during the previous week. The global score is based on the sum of the negative mood states (tension, depression, anger, and fatigue) and the positive mood states (vigor). Athletes who experience overtraining have higher total POMS mood disturbance scores than athletes who do not [58]. POMS may predict which athletes are prone to OTS, but it remains unclear whether POMS can predict overtraining in all athletes, as some athletes appear to experience alterations in mood without declines in performance [60]. In addition, POMS testing may not be practical for all athletes and coaches.

The TQR score is a useful tool for monitoring whether an athlete's recovery from training is adequate [2]. TQR scoring sheets can be obtained from several websites, including one in the following reference [61]. The TQR can be subdivided into the TQR action (TQRact) and TQR perceived (TQRper). The TQRact score is a self-reported assessment of recovery in four major areas: nutrition and hydration, sleep and rest, relaxation and emotional support, and stretching and active rest. The TQRper score uses a scale similar to the Borg Relative Perceived Exertion Scale, where the athlete reports their overall perception of recovery, which can be adjusted according to individual differences. The combination of TQRact and TQRper enables the coach or athlete to assess continually the adequacy of recovery and readiness for continued high-intensity training.

The REST-Q gauges the frequency of both current stress symptoms and recovery-associated activities/states of the previous three days and nights and addresses both nonspecific and sport-specific areas of stress and recovery. The questionnaire includes 76 statements that are divided into seven general stress scales (eg, "General Stress"), five general recovery scales (eg, "Physical recovery"), three sport-specific stress scales (eg, "Emotional Exhaustion"), and four sport-specific recovery scales (eg, "Self-regulation"). In addition, the Acute Recovery and Stress Scale (ARSS) and the Short Recovery and Stress Scale (SRSS) have been developed as concise measures of recovery and stress that can be used for a longitudinal assessment of the acute recovery-stress state [62].

Physiologic markers of overtraining — Several physiologic markers for overtraining have been studied, but no single marker or combination of markers can be used to establish the diagnosis of OTS. Among the markers studied are resting and post-exercise heart rate, heart rate variability (HRV), maximal heart rate achieved during exercise, and resting and exercise oxygen consumption (VO₂) [63,64]. Resting heart rate has too many confounding variables (eg, fever, illness, stimulant use) to be a consistently useful marker, but some coaches and athletes use it as part of their monitoring for overtraining. (See "Evaluation of heart rate variability".)

Another sign of an increase in sympathetic tone may be a change in HRV. A meta-analysis evaluated HRV as well as a number of other cardiac changes parameters and found that while small changes may be demonstrated in a research setting, the clinical utility of these tools is yet to be determined [65]. The recommendation of the authors was that these tools should be used in conjunction with other signs or symptoms.

Biochemical markers of overtraining — A number of biochemical markers have been studied for their usefulness in predicting OTS, but no single marker or combination of markers can be used to establish the diagnosis. Creatine kinase (CK) was once thought to be a good indicator of overtraining [66]. High CK levels indicate increased permeability from muscle cell membrane damage due to intense exercise. However, such elevations are common in normal athletes without performance impairment following training and have been absent in some athletes with OTS. Similarly disappointing findings have been noted in studies of hemoglobin/hematocrit, red blood cell counts, serum cortisol and testosterone, serum ferritin, serum lactate, and growth hormone [67,68]. The plasma testosterone/cortisol ratio decreases with heavy training loads and is thought to reflect the strain of a training load better than other hormonal measures. However, a low ratio is not diagnostic of OTS [5].

Glutamine is an amino acid that becomes depleted during catabolic states (eg, infection, trauma, acidosis). Athletes with OTS often have low glutamine levels, so glutamine is being studied as a potential marker of overtraining [69-71]. If recovery between training sessions is inadequate, glutamine levels cannot be replenished. However, further study is needed as confounding factors (eg, diurnal measurement variations, diet, infection) can alter glutamine metabolism.

Sleep monitoring — Sleep may be monitored via the use of a sleep diary or actigraphy [43]. The Consensus Sleep Diary was created by panel of sleep experts and represents a standardized diary for use in various populations. If a medical sleep disorder such as obstructive sleep apnea (OSA) or restless legs syndrome (RLS) is suspected, referral to a sleep specialist is recommended. (See "Evaluation and diagnosis of insomnia in adults", section on 'Evaluation' and "Clinical presentation and diagnosis of obstructive sleep apnea in adults" and "Clinical features and diagnosis of restless legs syndrome and periodic limb movement disorder in adults".)

SPECIAL CONSIDERATIONS IN THE YOUNG ATHLETE — The presentation and management of the spectrum of overtraining problems (eg, functional overreaching, nonfunctional overreaching, and overtraining syndrome [OTS]) are similar in younger athletes. However, compared with adults, younger athletes may have difficulty describing their symptoms. Thus, it is important for the clinician to spend time with a younger athlete and to ask specifically about symptoms and signs of overtraining or overreaching, such as persistent or unexpected levels of fatigue after exercise, difficulty with sleep, changes in mood, and problems with schoolwork or decline in academic performance. The clinician should inquire about the observations of others in regular contact with the athlete (eg, teachers, parents, coaches), who may share them directly with the clinician or have mentioned them to the athlete. Younger athletes are less likely to be monitored carefully for fatigue due to school and other scheduling factors, and they may not have adequate opportunities for recovery and sleep.

In addition to physical overtraining, emotional burnout is an important concern among young athletes and can contribute to OTS. A position statement from the American Medical Society for Sports Medicine (AMSSM) and other publications describe features that are common to burnout in young athletes, including the following [18,40,72,73]:

●Psychological and family factors:

•Low self-esteem

•Particular personality traits, such as perfectionism or a need to please others

•Identity based primarily on sports performance

•Loss of personal control (ie, performance expectations determined by coaches and parents)

•Increased worry about failure and adult expectations

•Parental pressure

•Overscheduling

●Sports-related factors:

•Extremes of training intensity and time demands

•Frequent competition

•Sport specialization at a young age

•Negative performance evaluations

Excessive stress from sport can lead to loss of sleep and appetite, decreased fun and satisfaction, physical injury, lower performance, and ultimately, withdrawal from the sport. As there is a strong psychological component to burnout in children, we recommend early consultation with a sports psychologist whenever possible [40].

SUMMARY AND RECOMMENDATIONS

●Definitions and key concepts – Overtraining syndrome (OTS) is an incompletely understood syndrome manifested by systemic symptoms and declining performance. OTS is best avoided by ensuring that athletes recover properly from intense training. Recovery requires adequate hydration and nutrition, sleep and rest, relaxation and emotional support, and active somatic/physical rest. A number of concepts related to proper athletic training and the prevention of OTS are reviewed in the text. (See 'Definitions and principles of athletic training' above.)

The following terminology is widely used to describe responses to overload training and related disorders:

•Acute fatigue – Acute fatigue is the immediate result of overload training. Although fatigued, the athlete experiences no perceivable decline in performance.

•Functional overreaching – Overreaching is broadly defined as a short-term decrement in athletic performance after a period of overload training. Functional overreaching (FOR) is a short-term (less than two weeks), training-induced increase in fatigue and decline in performance that is transient and associated with increased training loads.

•Nonfunctional overreaching (NFOR) – Nonfunctional overreaching (NFOR) is defined as intense overload training that leads to a longer period of decreased performance than FOR (typically two weeks to two months), but adequate rest leads to a full recovery. NFOR is frequently accompanied by increased psychological and/or neuroendocrine symptoms of the type associated with overtraining, whereas FOR is usually not.

•Overtraining syndrome – OTS (also referred to as "staleness" or "burnout") is defined as a prolonged (usually greater than two months) decline in sport-specific performance.

●Theories about etiology – No single theory adequately explains the etiology of OTS. Commonly cited theories include the autonomic imbalance hypothesis, glycogen depletion hypothesis, branched-chain amino acid (BCAA) hypothesis, glutamine hypothesis, and cytokine hypothesis. (See 'Current theories and physiology' above.)

●Clinical presentation – Symptoms and signs associated with OTS are summarized in the following table (table 1). OTS involves unexplained underperformance and subjective complaints that may include persistent fatigue, increased sense of effort during training or competition, sleep disturbance and increased daytime sleepiness, persistent muscle soreness, lack of motivation, depression, irritability, lack of cooperation with teammates or coaching staff, and difficulty concentrating. Physical examination is often normal. Other physical findings may include chronic or recurrent overuse injuries, anorexia, weight loss, and signs of respiratory infection (due to increased susceptibility). (See 'Clinical presentation' above.)

●Diagnosis and differential diagnosis – There are no widely accepted guidelines for establishing the diagnosis of OTS. Evaluation of the fatigued athlete often requires several clinic visits during which the clinician carefully considers the differential diagnosis, which is potentially broad. Key elements of the differential include nutritional deficiency, iron deficiency with or without anemia, psychological problems (eg, depression), and other medical problems (eg, hypothyroidism, cardiomyopathy, myocarditis, infectious mononucleosis). Important clinical features that help to distinguish alternative diagnoses from OTS are described in the text. (See 'Differential diagnosis' above and 'Diagnosis' above.)

●Diagnostic evaluation – Evaluation of the athlete who may have OTS includes a careful history, including the training program, diet, medications, recent or chronic illness, and a thorough review of systems (ROS). The goals and implementation of the athlete's training program are reviewed in detail. It is important to ask about any recent increase in the frequency, duration, or intensity of training prior to the onset of symptoms. A sensible initial laboratory evaluation includes a complete blood count, serum or plasma ferritin concentration, basic metabolic panel (including serum sodium, chloride, potassium, and bicarbonate; and creatinine and blood urea nitrogen [BUN]), and thyroid-stimulating hormone (TSH). Other laboratory studies may be indicated based upon the history, but extensive testing is usually not required. Proper assessment typically requires several weeks, and the athlete should substantially decrease the intensity of their training or observe absolute rest during that time. (See 'Diagnostic evaluation' above.)

●Management – The optimal management of patients with OTS is not known; treatment is based to a large extent on clinical experience and intuition. There is no "quick fix" for OTS. Ultimately, rest may be curative. Early intervention in athletes with FOR or NFOR can help avoid the need for a protracted recovery from OTS. If an athlete experiences signs of fatigue and declining performance, decreasing the training intensity by 50 to 75 percent for one to two weeks may result in improved performance. If symptoms are more severe, of longer duration, or have failed to respond to decreased training intensity, more significant restrictions are likely to be needed, including abstaining from all competitive training. (See 'Treatment' above.)

●Prevention and monitoring – While monitoring athletes for overtraining is important, no single reliable indicator of OTS has been identified. Many experts suggest using a combination of tools. For athletes involved in intense training and thought to be at increased risk of OTS, the author suggests regular assessment of training and well-being, including regular use of a formal psychological assessment tool (either Total Quality Recovery [TQR] or the Recovery Stress Questionnaire [REST-Q]). Additional techniques for prevention and monitoring are reviewed in the text. (See 'Prevention and monitoring' above.)

●Considerations in youth athletes – The presentation and management of the spectrum of overtraining problems (FOR, NFOR, OTS) do not differ significantly in adolescents. In addition to OTS, emotional burnout is an important concern in youth athletes and can contribute to OTS. (See 'Special considerations in the young athlete' above.)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Thomas M Howard, MD, FACSM, who contributed to an earlier version of this topic review.