Overtraining and Marathon Running
When training for a marathon an athlete must apply regular exercise-based stress to their body in order to increase their performance, using a method known as functional over-reaching (FO) (Meeusen et al., 2006). FO is where a high degree of stress is placed upon the athlete, resulting in acute fatigue and temporarily reduced performance, but when balanced out with optimal recovery a supercompensation effect occurs where the body adapts and performance improves (McFarlane, 1985).
However if an imbalance occurs between this stress and recovery, and the acute fatigue is not managed it can lead non-functional over-reaching (NFO), a chronic form of fatigue that can take several weeks to recover from and elicits no performance improvements (Meeusen et al., 2006). Due to the high mileage endured as part of their training, it is estimated that around 65% of distance runners will suffer from NFO sometime in their career (McKenzie, 1999).
When an athlete is in a state of NFO and stress is continually applied, it is possible for them to become over-trained. Over-training is also known as the unexplained underperformance syndrome (UUPS) as it is unclear what the specific cause is, and is difficult to diagnose due to its similarities to NFO. The definition of UUPS is a reduction in an athlete’s performance with no improvement after six weeks of rest (whereas NFO is alleviated in this period) (Budgett, 2000), and is characterised as an abnormal response to training.
It should be noted that UUPS is multifactorial, and involves other stressors in addition to exercise, such as inadequate nutrition, illness, psychosocial stressors and sleep disorders, which will need to be accounted for and monitored.
Symptoms of UUPS (Kreher & Schwartz, 2012)
– An unexplained decline in performance
– A recent intense training cycle
– Upper respiratory tract infections (cough, sneeze, sore throat)
– Muscle soreness or feelings of tightness/heaviness
– Altered moods – depression, lack of motivation, lethargy, confusion
– Poor sleep quality/quantity
– Low energy and vigour
– No desire to train or compete
– Changes in appetite/desire to eat
Note: Symptoms of UUPS are individual and it should be down to the athlete, coach and other relevant team/family members to make a diagnosis.
It must be made certain that the athlete is not suffering from any organic diseases or disorders such as, for example, endocrinological/hormone disorders (such as diabetes), anaemia or eating disorders (bulimia or anorexia nervosa), asthma or undiagnosed infections.
Causes of UUPS
Imbalance of the Autonomic Nervous System (ANS)
The ANS is a branch of the peripheral nervous system that regulates the function of our internal organs (heart, stomach, intestines), it incorporates the two commonly heard phrases ‘fight or flight’ and ‘rest and digest’. The ‘fight or flight’ aspect is the sympathetic nervous system, it mediates stress responses and an imbalance (dominance) in this system results in it being constantly ‘switched on’ at rest, causing restlessness and hyper-excitability.
The ‘rest and digest’ aspect is the parasympathetic nervous system, and dominance of this system is more common in marathon runners, causing fatigue, mood disturbances and prolonged recovery (Bosquet, Papelier, Leger, & Legros, 2003). This mechanism seems unlikely however, as a study by Pichot (2000) shows an abrupt recovery of symptoms within a week of rest.
A disturbance to the hypothalamic-pituitary-adrenal (HPA) axis has been indicted as a potential mechanism of UUPS (Kreher & Schwartz, 2012). The HPA axis is a major part of the neuroendocrine system that controls reactions to stress and regulates bodily processes such as the immune system, mood, and energy storage, and is responsible for the production of adrenocorticotrophic hormone (ACTH), cortisol and testosterone.
Cortisol and testosterone are catabolic and anabolic (respectively), catabolic meaning that it breaks down muscle and anabolic the opposite. Cortisol rises during endurance exercise and negatively affects immune function and the production of testosterone (Karkoulias, 2008). Findings are mixed as to whether changes in these hormones relate to UUPS (Mackinnon, Hooper, Jones, Gordon, & Bachmann, 1997; Uusitalo, Huttunen, Hanin, Uusitalo, & Rusko, 1998) however an imbalanced testosterone:cortisol ratio (low testosterone, high cortisol) does indicate the physiological strain of exercise (Halson & Jeukendrup, 2004).
Periods of over-reaching cause a decreased level of immune function for a short period following exercise, this ‘open window’ of immune function is largest in endurance athletes (such as marathon runners) due to the prolonged nature of the sport (Gleeson, 2007). Indicators of this immunodepression include upper respiratory tract infections (URTIs) (Matthews, 2002) such as sore throats, coughs and sneezes. This could be due to a decrease in immunoglobulin-a (Ig-A), an anti-body found in mucus/saliva (i.e. in the nose, mouth, gastrointestinal tract) that can be diminished due to intense exercise (Gleeson, 2007).
Smith (2000) suggested a ‘cytokine hypothesis’ whereby intense exercise causes damage to muscles/bones/joints causing widespread inflammation which releases cytokines, signalling molecules that promote inflammation, such as interleukin-6 (IL-6). An elevation in cytokines can have a large number of effects on the body, including ‘sickness behaviour’ due to effects on hormones, reduced glucose transport to muscles, and disruptions in the testosterone:cortisol ratio, all of which lead to feelings of fatigue and symptoms of UUPS. Scientific evidence of this is sparse and has shown that cytokine levels are not imbalanced in over-reached athletes (Halson, Lancaster, Jeukendrup, & Gleeson, 2003) although the same study suggests that decreases in glutamine, an amino acid that is beneficial in many ways to the body, may be indicative of UUPS.