Soccer superstar Landon Donovan (right) has been the face of American soccer for the last 10 years. He recently stunned soccer fans by taking a break from the beautiful game citing mental and physical exhaustion. Landon Donovan's public lack of motivation and mental and physical fatigue are surely signs of overtraining syndrome. Fortunately, after several months of rest he was able to return to the pitch. Here we discuss overtraining's effect on the athletes' performance, cognition and mood. In addition, scientists have recently isolated a molecule that may be responsible for overtraining syndrome.
Overtraining syndrome is prevalent throughout athletics, regardless of sport. Studies have shown that over half of professional soccer players will experience overtraining syndrome during a season, 60% of distance runners will experience overtraining syndrome at some point in their career and a third of athletes at a six week basketball camp experienced overtraining syndrome. Overtraining occurs in both high volume training regimens, like swimming programs, and high intensity training regimens, like weightlifting. Overtraining refers to the act of training above the body's capacity for recovery which results in overtraining syndrome. As with any disease or disorder, the first question to ask is what are the signs and symptoms of overtraining syndrome?
What is interesting about these symptoms is that researchers currently believe that overtraining can take one of two routes depending on the style of training: overtraining syndrome through the sympathetic nervous system or the overtraining syndrome via the parasympathetic nervous system. Both are divisions in the body's autonomic nervous system. The sympathetic nervous system is responsible for fight-or-flight response: elevating heart rate, releasing adrenaline and blood vessel constriction at the digestive organs among other functions. The parasympathetic nervous system is primarily active while at rest and essentially slows down the heart rate and activates the digestive and other housekeeping organs. It is believed that high volume aerobic training can bring on parasympathetic overtraining symptoms such as fatigue. High intensity training leads to sympathetic overtraining symptoms such as excitability, anxiety and insomnia. Whether through high intensity or high volume training, understanding how to prevent overtraining syndrome is naturally beneficial to athletes and their coaches.
Maintaining a balance between training at a sufficient intensity or volume to generate increased performance without leading to overtraining syndrome often requires that coach and athlete work together to individualize a training program. Undertraining and acute overload do not produce the desired performance improvement. To produce an optimal improvement in athletic performance the athlete must train by overreaching: stressing the body through muscle overload, but with proper rest for recovery. Training above the body's capacity for recovery, overtraining, is detrimental to performance and leads to overtraining syndrome. The figure below, adapted from a great review on the subject (The Unknown Mechanism of the Overtraining Syndrome, 2002. Armstrong and VanHeest), demonstrates the effects that increasing training intensity or volume has on the body and performance.
ExerciseMed has discussed immunity weakness following prolonged exercise, called the open window theory, and chronic fatigue brought on by glycogen depletion. Apparently, neither of these physiological deficiencies are responsible for overtraining syndrome. Clues on the root of overtraining syndrome can be found in its similarity to other psychological disorders. The way the body reacts to overtraining follows the pattern laid out by general adaptation syndrome: alarm, resistance and exhaustion. Each stage is founded upon hormone imbalances. Mood imbalance is another factor. A ten-year study found that college swimmers' scores on a profile of mood states test rose in a dose-dependent manner with training volume over the course of the competitive swimming season, only returning to baseline at the conclusion of the season (Psychological monitoring of overtraining and staleness, 1987. Morgan, et al.). Perhaps the most striking lead to the physiological nature of overtraining syndrome comes from its similarity to major depression.
Many of the characteristics of overtraining symptom overlap with major depression. In fact, 80% of the overtrained swimmers in Morgan's study were found to be clinically depressed; that is, depressed according to diagnosis with their signs and symptoms. Besides the signs and symptoms, biochemical markers are similar as well. Blood cortisol levels are decreased in both overtraining syndrome and major depression. Epinephrine levels are also altered in both. The adrenal dysfunction (responsible for epinephrine) and cortisol reduction implicate two separate neuroendocrine axis: the sympathetic-adrenal medullary and the hypothalamic-pituitary-adrenocortical axis. Neurotransmitter serotonin and its predecessor tryptophan are altered by both disorders, either in production or reception. Furthermore, anti-depressants have successfully been used to treat both the physical and psychological components of overtraining syndrome in elite athletes.
Recently, much excitement has been generated in the neurology and physiology communities over exercise-induced neurogenesis and brain plasticity. While exercise increases neurogenesis, overtraining and major depression alike result in reduced brain plasticity and neural retraction in animal models. One potential candidate for causing this exercise effect is AMPK agonist 5-Aminoimidazole-4-carboxyamide-1-Beta-D-ribofuranoside (AICAR). Interestingly, 7 days of treatment with AICAR on mouse models produced neurogenesis and enhanced memory, but 14 days of treatment diminished this effect (Muscle fatigue and cognition:what is the link? 2012. Kobilo and van Praag). However, because AICAR cannot cross the blood brain barrier it likely acts through another, as of now, unknown signaling molecule.
Understanding overtraining syndrome is fruitless without understanding how to treat it. It is important to realize that outside stressors play a role in overtraining syndrome. The best defense is to keep outside stress to a minimum. If this is not possible due to occupational or family obligations, it may be a good idea to reduce training volume or intensity during periods of high outside stress. Keep the body healthy: stay hydrated, maintain caloric balance, and keep up on sleep. Whether an athlete or the athlete's coach or doctor, be aware of the psychological state of the athlete through conversation or mood questionnaires. Finally, treat overtraining syndrome with rest. The longer the overtraining syndrome has occurred, the longer the rest treatment needed.
Researchers are just beginning to understand the complexities of overtraining syndrome, this young exercise physiology frontier will yield new discoveries through cross-disiplinary research.