Aerobic Physical Exercise
Physical Exercise

Runner's high
A publicized effect of endorphin production is the so-called "runner's high", which is said to occur when strenuous exercise takes a person over a threshold that activates endorphin production. Endorphins are released during long, continuous workouts, when the level of intensity is between moderate and high, and breathing is difficult. This also corresponds with the time that muscles use up their stored glycogen. During a release of endorphins, the person may be exposed to bodily harm from strenuous bodily functions after going past his or her body's physical limit. This means that runners can keep running despite pain, continuously surpassing what they once considered to be their limit. Runner's high has also been known to create feelings of euphoria and happiness.
Runner's high has been suggested to have evolutionary roots based on the theory that it helped with the survival of early humans. Runner's high allows humans to run for vast lengths without pain. Most early humans hunted and gathered for their food. This required them to cover vast distances hunting down their prey or foraging for their food. This could have caused them to develop conditions such as shin splints and stress fractures in their shin and feet bones. Without runner's high to negate the pain caused by running on bones with these conditions, early humans theoretically would not have been able to repeatedly cover these vast distances in search of their food and thus would have starved. Current African tribes make use of runner's high when conducting persistence hunting. Persistence hunting is a method of hunting in which tribesman hunt an animal and track it for many miles, normally around 10 miles, eventually killing the animal due to its vulnerability brought on by exhaustion.
In 2008, researchers in Germany reported on the mechanisms that cause the runner's high. Using PET scans combined with recently available chemicals that reveal endorphins in the brain, they were able to compare runners’ brains before and after a run. (The runner’s high: opioidergic mechanism in the human brain 2008)
It is also suggested by many that endorphins are some of the many chemicals that contribute to runner's high; other candidates include epinephrine, serotonin, and dopamine.
Endocannbinoids are the chemical most likely responsible for causing runner's high if endorphins are proved to not cause runner's high. Endocannabinoids are the body's natural chemical that interacts with the same brain receptor responsible for causing the high associated with marijuana use. In tests by the Institute of Georgia it was shown that endocannabinoid receptors were necessary for cognitive improvements due to exercise to occur. It is also shown that the endocannabinoids are involved in the reward system of the body, controlling the rewards for both exercise and consuming dessert. Another experiment that supports the endocannabinoid theory is that when mice were bred without the endocannabinoid receptor they ran thirty to forty percent less than regular mice. The only issue with the endocannabinoid theory is that it shows motivation and reward for running more than mood change, not eliminating it from the discussion of causes of runner’s high, but does not place it in the frontrunner position for causation.
Previous research on the role of endorphins in producing runner's high questioned the mechanisms at work, their data possibly demonstrated that the "high" comes from completing a challenge rather than as a result of exertion. (Does placebo response mediate runner's high? 1986)
Studies in the early 1980s cast doubt on the relationship between endorphins and the runner's high for several reasons:
- The first was that when an antagonist (pharmacological agent that blocks the action for the substance under study) was infused (e.g., naloxone) or ingested (naltrexone) the same changes in mood state occurred as when the person exercised with no blocker.
- A study in 2003 by the Georgia Institute of Technology found that runner's high might be caused by the release of another naturally produced chemical, anandamide. The authors suggest that the body produces this chemical to deal with prolonged stress and pain from strenuous exercise, similar to the original theory involving endorphins. However, the release of anandamide was not reported with the cognitive effects of the runner's high; this suggests that anandamide release may not be significantly related to runner's high. (Exercise activates the endocannabinoid system 2003)
Runner’s high is a phenomenon that was vital to our very survival back in primitive times, and is still crucial to the survival of some and the enjoyment in recreational running. While there are many theories as to what is the cause of the phenomenon, endorphins have the most decisive evidence to support it being the cause. Endocannabinoids are a likely cause as to the motivation behind why we run but not why runner’s high occurs. (Endocannabinoids and voluntary activity in mice: runner's high and long-term consequences in emotional behaviors. 2010) Even though the most probable individual cause of runner's high is endorphins, it is more likely a cocktail of chemicals reacting in the brain along with the overtaxing of the brain’s information processing capabilities that produces the phenomenon known as runner’s high.
A recent study analyzed the correlation between endocannabinoids and the regulation of hypothalamic-pituitary-adrenal axis. The endocannabinoids system seems to be involved in the central regulation of stress response. (Endocannabinoid signaling, glucocorticoid-mediated negative feedback, and regulation of the hypothalamic-pituitary-adrenal axis. 2011) Moreover, it has be found that during intense exercise levels of circulating endocannabinoids are increased and this might be related with antidepressant effects of exercise. (Intense exercise increases circulating endocannabinoid and BDNF levels in humans-Possible implications for reward and depression. 2011)

Bibliography
PubMed
Wikipedia

Physical exercise and brain

Some reviews of the literature on the relationship of exercise to mental health strongly suggest that the two are closely linked. In fact, physical activity has been reported to reduce depression and anxiety.
A lot of hypothesis have been suggested, one of those, the most important, is related to endorphine and monoamine systems.
In the United Kingdom the National Institute for Health and Clinical Excellence, which works on behalf of the National Health Service and makes recommendations on treatments according to the best available evidence, has published a guide on the treatment of depression. The guide recommends treating mild clinical depression with various strategies, including exercise rather than antidepressants, because the risk–benefit ratio is poor for antidepressant use in patients with mild depression. Exercise improves mood in subclinical populations as well as in patients. The most consistent effect is seen when regular exercisers undertake aerobic exercise at a level with which they are familiar. However, some skepticism remains about the antidepressant effect of exercise, and the National Institute of Mental Health in the United States is currently funding a clinical trial of the antidepressant effect of exercise that is designed to overcome sources of potential bias and threats to internal and external validity that have limited previous research.
For example, Chaouloff and colleagues showed that exercise increased tryptophan and 5-HIAA in rat ventricles. More recent studies using intracerebral dialysis have shown that exercise increases extracellular serotonin and 5-HIAA in various brain areas, including the hippocampus and cortex. Two different mechanisms may be involved in this effect. As reviewed by Jacobs and Fornal, motor activity increases the firing rates of serotonin neurons, and this results in increased release and synthesis of serotonin. In addition, there is an increase in the brain of the serotonin precursor tryptophan that persists after exercise.

Physical exercise and brain monoamines: a review
September 1989

The increasing of Tryptophan has thought to be related to the rising of the lipidic catabolism during exercise and as a result, the increased level of fatty acids in the blood. These fatty acids are transported by albumin, and they displaced tryptophan, which also travels linked to this serum protein. The tryptophan can pass the ematoencephalic barrier and can be used in the synthesis of serotonin.

Effects of acute physical exercise on centrale serotonergic systems.
January 1997

Physical exercise: evidence for differential consequences of tryptophan on 5-HT synthesis and metabolism in central serotonergic cell bodies and terminals
1989

W. Hofmann, from the Institute of Sportive Medicine of The University of Colonia, in the'80s demonstrated that continuous exercise has got a positive action, above all, on cardiopulmonary system, saying: “ A forty years old man who practices regular activity at the age of sixty will be still biologically a forty years old man.” This is true for the immunity system too.
Moderate and continuous physical activity stabilizes the immunity system, by regenerating and stimulating leukocytes. In addition, exercises increase self-consciousness, decrease anxiety and lead to psychic stabilization, supported by rising of endorphines.

Moderate activity doesn't lead to an excessive increase of cortisol, which is the ”hormone of the stress”.
In conclusion there are sufficient evidence for the effectiveness of exercise in the treatment of clinical depression. Additionally, exercise has a moderate reducing effect on anxiety and can improve physical self-perceptions and mood states in the general population. The aerobic exercise improves health by reducing heart disease, obesity, diabetes and by enhancing mood.

The influence of physical activity on mental well-being
September 1999