The little research that does exist on children and marathons does not seem to indicate that all children should be prohibited from doing so. Children who do have the desire to work toward this goal should be given an appropriate and progressive training program, have the consent of their parents or guardians, ingest necessary nutrients to continue normal development, and be closely monitored for signs and symptoms of injury and burnout.
One common concern regarding marathons is the increased susceptibility to the common cold and upper respiratory tract infections (URTIs). The "Window of Opportunity" theory states that, due to the extreme demands place upon the body, a runner's risk of catching the common cold or experiencing a URTI is elevated for as long as 2 weeks after the marathon ends. In contrast, a person who engages in moderate, less strenuous, physical activity will only experience a slight risk elevation and for a much shorter timer period.
It appears that, in marathon runners, there is a decline in the level of different immune cells (blood natural killer cells and T-cells, for instance) and a marked increase in stress hormones (cortisol, in particular). Changes in body temperature, lack of fluid ingestion, death of certain lymphocytes, and an exercise-induced increase in blood flow also may increase a runner's likelihood of dealing with some sort of illness after his or her race. The percentages of adult runners who report experiencing some sort of illness or infection after a marathon range from 3% to 25%. It is probably that children will be at a slightly higher risk of developing an infection. These concerns are even more valid when it comes to children and marathon training. Children, due to a lack of development, typically have greater difficulty in coping with infections. Furthermore, proper instruction and training is absolutely crucial in terms of ensuring that these children ingest enough carbohydrates and fluids while training for marathons. They also need to be closely monitored in terms of getting enough recovery time.
What is important to understand is that, provided runners avoid over-training, they will not typically elevate their risk of infection significantly. Other types of stress related to the marathon should also be points of consideration (a recent exposure to an unfamiliar germ, mental stress and exhaustion, unhealthy weight loss, improper nutritional or fluid intake, and fewer hours of quality sleep) in terms of predicting the likelihood of an infection. Once again, children may be more susceptible to these stressors if they are not carefully monitored by their guardians and/or coaches. Also, based upon the severity of the experienced illness, taking a break from training (up to 4 weeks) may be advisable. Finally, it has been shown that adequate ingestion of healthful carbohydrates is an effective way to prevent colds and URTIs. Thus, in the case of children and marathons, adequate nutrition is even more critical because, depending upon their ages and genetics, they must take in enough calories to sustain and promote normal development while also ensuring success while training and competing.
To be continued in Part 3