Physical exercise

 is any bodily activity that enhances or maintains physical fitness and overall health and wellness. It is performed for various reasons. These include strengthening muscles and the cardiovascular system, honing athletic skills, weight loss or maintenance and for enjoyment. Frequent and regular physical exercise boosts the immune system, and helps prevent the "diseases of affluence" such as heart disease, cardiovascular disease, Type 2 diabetes and obesity.^[1][2] It also improves mental health, helps prevent depression, helps to promote or maintain positive self-esteem, and can even augment an individual's sex appeal or body image, which again is also linked with higher levels of self-esteem.^[3] Childhood obesity is a growing global concern^[4] and physical exercise may help decrease the effects of childhood obesity in developed countries.

Girls on the Run

is a North American non-profit program that works to encourage pre-teen girls to develop self-respect and healthy lifestyles through participation in running programs. The organization’s curricula seek to address all aspects of the girls’ development to enhance their physical, emotional, mental, social, and spiritual well-being.

Local chapters operate under an umbrella organization, Girls on the Run International, which develops curricula and provides support to the local chapters while encouraging the formation of additional chapters in areas not yet served by the program. International has received inquiries from at least 43 countries around the world.

Program of Girls on the Run

The standard curriculum is divided into three parts:^[1]

The first eight lessons are centered on the participants’ getting to know themselves. They are encouraged to examine their values, their likes and dislikes, and how they envision themselves. As the girls get to know themselves, they are also share with each other. Lesson topics and learning goals include "fueling our healthy pace", "centering: the importance of slowing down", and "celebrating gratitude".

The next eight lessons concentrate on team building, being supportive, learning to listen and cooperate, etc. Lesson topics and learning goals include "standing up to peer pressure", "gossiping hurts everyone", and "it’s okay to choose my friends."

The final eight lessons relate to the world at large. This includes making a contribution to one’s community and learning to recognize and deal with the negative messages people, and especially girls, often receive from the world (media awareness, negative peer pressure, etc.). Lesson topics and learning goals include "learning about community", "tuning into a new message" (media literacy), and the development and implementation of a group community project.

The season's activities include training to participate in the 5k run which caps off the program. These runs typically involve participants from the whole community,^[12] including the girls' "buddy runners",^[13] parents, and friends. Over 100 running events were organized in 2010;^[14] more are scheduled for 2011.
To keep the curriculum age-appropriate, Girls on the Run operates two programs for its participants. “Girls on the Run” is for 3rd–5th graders (approximately 8 through 10 years old). “Girls on Track” is directed to 6th–8th graders (11 through 13 years old).^[1][15

Excessive exercise

Exercise is a stressor and the stresses of exercise have a catabolic effect on the body—contractile proteins within muscles are consumed for energy, carbohydrates and fats are similarly consumed and connective tissues are stressed and can form micro-tears. However, given adequate nutrition and sufficient rest to avoid overtraining, the body's reaction to this stimulus is to adapt and replete tissues at a higher level than that existing before exercising. The results are all the training effects of regular exercise: increased muscular strength, endurance, bone density, and connective tissue toughness.
Too much exercise can be harmful. Without proper rest, the chance of stroke or other circulation problems increases,^[43] and muscle tissue may develop slowly. Extremely intense, long-term cardiovascular exercise, as can be seen in athletes who train for multiple marathons, has been associated with scarring of the heart and heart rhythm abnormalities.^[44][45][46]
Inappropriate exercise can do more harm than good, with the definition of "inappropriate" varying according to the individual. For many activities, especially running and cycling, there are significant injuries that occur with poorly regimented exercise schedules. Injuries from accidents also remain a major concern,^[47] whereas the effects of increased exposure to air pollution seem only a minor concern.^[48][49]
In extreme instances, over-exercising induces serious performance loss. Unaccustomed overexertion of muscles leads to rhabdomyolysis (damage to muscle) most often seen in new army recruits.^[50] Another danger is overtraining in which the intensity or volume of training exceeds the body's capacity to recover between bouts.^[51]
Stopping excessive exercise suddenly can also create a change in mood. Feelings of depression and agitation can occur when withdrawal from the natural endorphins produced by exercise occurs. Exercise should be controlled by each body's inherent limitations. While one set of joints and muscles may have the tolerance to withstand multiple marathons, another body may be damaged by 20 minutes of light jogging. This must be determined for each individual.
Too much exercise can also cause a female to miss her period, a symptom known as amenorrhea.^[52]

Effects on depression

A number of factors may contribute to depression including being overweight, low self-esteem, stress and anxiety.^[34] Endorphins act as a natural pain reliever and antidepressant in the body.^[35] Endorphins have long been regarded as responsible for what is known as "runner's high", a euphoric feeling a person receives from intense physical exertion.^[36] However, recent research^[16][17] indicates that anandamide may possibly play a greater role than endorphins in "runner's high". When a person exercises, levels of both circulating serotonin and endorphins are increased.^[37] These levels are known to stay elevated even several days after exercise is discontinued, possibly contributing to improvement in mood, increased self-esteem, and weight management.^[36] Exercise alone is a potential prevention method and/or treatment for mild forms of depression.^[38]

Effect on the immune system

Although there have been hundreds of studies on exercise and the immune system, there is little direct evidence on its connection to illness. Epidemiological evidence suggests that moderate exercise has a beneficial effect on the human immune system while extreme exercise impairs it, an effect which is modeled in a J curve. Moderate exercise has been associated with a 29% decreased incidence of upper respiratory tract infections (URTI), but studies of marathon runners found that their prolonged high-intensity exercise was associated with an increased risk of an infection, although another study did not find the effect. Immune cell functions are impaired following acute sessions of prolonged, high-intensity exercise, and some studies have found that athletes are at a higher risk for infections. The immune systems of athletes and nonathletes are generally similar. Athletes may have slightly elevated natural killer cell count and cytolytic action, but these are unlikely to be clinically significant.^[24]
Vitamin C supplementation has been associated with lower URTIs in marathon runners.^[24]
Biomarkers of inflammation such as C-reactive protein, which are associated with chronic diseases, are reduced in active individuals relative to sedentary individuals, and the positive effects of exercise may be due to its anti-inflammatory effects. The depression in the immune system following acute bouts of exercise may be one of the mechanisms for this anti-inflammatory effect.^[24

Effect on the cardiovascular system

There is a direct relation between physical inactivity and cardiovascular mortality, and physical inactivity is an independent risk factor for the development of coronary artery disease. There is a dose-response relation between the amount of exercise performed from approximately 700 to 2000 kcal of energy expenditure per week and all-cause mortality and cardiovascular disease mortality in middle-aged and elderly populations. The greatest potential for reduced mortality is in the sedentary who become moderately active. Most beneficial effects of physical activity on cardiovascular disease mortality can be attained through moderate-intensity activity (40% to 60% of maximal oxygen uptake, depending on age). ... persons who modify their behavior after myocardial infarction to include regular exercise have improved rates of survival. ... Persons who remain sedentary have the highest risk for all-cause and cardiovascular disease mortality.