Running can prolong life and lower the risk of disabling conditions and diseases.
Zuma Press/Icon SMI
Running is beneficial to the brain. In laboratory animals, running has been linked with elevated levels of brain-derived neurotrophic factor, a compound that stimulates the healthy growth of nerve cells;42 running also promotes increased synaptic plasticity, or the ability of nerve cells to form new links with each other.43 In addition, running improves performance on spatial navigation learning tasks.44 There is also considerable evidence—at least in lab animals—that running leads to the creation of new nerve cells in the brain in defiance of the long-standing principle that the brain’s maximal nerve cell count is fixed at an early age.45 Thus, it is not surprising that running has been linked with upgraded cognitive performance.46
Furthermore, there is evidence that running reduces the risk of depression and has pronounced antianxiety effects.47 A positive effect of running on psychological health has been uncovered in cross-sectional studies and randomized clinical trials that have looked at the effectiveness of exercise as a treatment intervention. In such studies, running has been shown to reduce symptoms of depression and frequency of clinical depression especially among older adults.48 There is also evidence that running and other forms of exercise can facilitate the restoration of normal function following serious brain injury.49
Conclusion
Running upgrades physiological variables associated with fitness, but it also has profound overall effects on health. As discussed in this chapter, running has a profoundly positive effect on lowering the risk of coronary heart disease and can dramatically lower the chances of developing a plethora of cancers. Running fights obesity and disability, and it has strong antidepressant and antianxiety effects that are great for mental health. Running prevents hypertension and lowers the chances of developing diabetes. As such a simple activity that requires little technical skill and is easy to learn, running provides an amazing array of health benefits.
Chapter 42
Health Considerations for Special Running Populations
Running has unique effects on young athletes—and especially on young female athletes who engage in strenuous training. Concerns have been raised regarding the safety of long-distance running for children from the standpoints of musculoskeletal safety and thermal adaptation, and young female runners are at increased risk of the female athlete triad. Running during pregnancy has also stirred much debate with some studies linking running with poor health outcomes for the fetus. Older runners recover less quickly from strenuous training, compared with their younger counterparts, and thus may be at greater risk of running-related injury.
Younger Runners
Exercise scientists have debated whether long-distance running is a healthful activity for children. Some experts suggest that prolonged running harms developing joints and active growth plates in bones. However, the Kenyan experience suggests that endurance running is not harmful to children and in fact promotes better health during young adulthood. Childhood running is a natural activity in Kenya, free from adult pressures and considered an essential aspect of life. Young Kenyan kids probably run greater distances than youngsters from any other part of the world and begin doing so at a very early age—often when they are just 5 years old or even younger.
Instead of experiencing bone, joint, and other problems, a high percentage of these children become extremely advanced—and healthy—distance runners, and many go on to become national- and international-level competitors. Compared to runners from Europe and the United States, young Kenyan runners appear to have lower rates of musculoskeletal injuries, including the shin splints, stress fractures, and bouts of plantar fasciitis that plague Western runners.1
When cast in Kenyan light, running appears to be a health-promoting rather than damaging activity for children. One reason for this may be that children’s running in Kenya is free from adult expectations; another is that the total training load is increased gradually as Kenyan children get older. It certainly cannot hurt that most childhood running in Kenya is carried out barefooted, which should build tremendous foot, ankle, and leg strength. Furthermore, barefoot running is almost always carried out with a midfoot-striking pattern, which diminishes the impact forces the legs must absorb on every foot strike.
The scientific research shows that young runners can engage in strenuous running training without endangering their long-term health as long as the running training is varied and gradually progressive in nature, includes precautions about heat stress, is associated with healthy eating practices, does not restrict calories, and is carried out without parental pressure. The desire to run long distances should originate with the child and not be the result of a parent’s desire for vicarious athletic experiences. Parents are strongly advised to provide emotional and practical support for their children’s running endeavors and to avoid pressuring young runners to meet high expectations.
Heating and Cooling
Science reveals that there are several problems associated with endurance training in young runners, however. The ratio of body surface area to mass (S/M) is higher in children than adults; with their smaller corporeal volumes, children have considerably more skin area per unit weight. This would seem to be advantageous for children since a higher S/M provides greater convective cooling. In effect, a child has relatively more skin from which he or she can transport heat to air flowing over the outside of the body compared with an average adult. Under very hot conditions, however, a high S/M can be a problem: The rate of heat transfer from the external world into the body can be increased. When the weather is cold, a high S/M also hikes the rate at which heat is lost to the outside world. A child engaged in a long run on a cold, windy day would have a significantly higher risk of hypothermia than an adult carrying out the same workout.5
Although they have relatively more skin area than adults, children have relatively less blood volume even when the total quantity of blood is expressed in relation to body weight. This effect could make exercise in the heat more demanding for children than adults since relatively reduced amounts of blood would be sent to the skin for cooling during exertion.
Children’s sweat glands also show diminished sensitivity to situations involving thermal stress, a condition that persists until about the age of 14. During approximately the first 13 years of life, the onset of sweating is delayed during strenuous exercise in the heat, and actual sweating rates are lower in children compared with adults. Children also do a poorer job of acclimatizing themselves to the heat: The extent of acclimatization achieved during 6 days of hot-weather exertion by adults might require 12 days for 8- to 10-year-old children.6 It is not surprising that what is commonly called heat stroke is believed to be the third leading cause of exercise-related death in young people after head injuries and cardiac disorders.5
Positive Training Effects
Despite the thermal disadvantages associated with being a young distance runner, there are actually many positives associated with endurance training in children. Young people who run on a regular basis usually enter adulthood with lower levels of body fat compared to their more sedentary counterparts, which appears to lower the risk of high blood pressure and type 2 diabetes during later life.5 Research also suggests that adult females who exercised regularly at a young age have a 60 percent lower risk of cancers of the uterus, ovaries, cervix, and vagina compared with nonexercisers and about a 50 percent reduction in breast cancer risk.5
Running’s Impact on Autism
Science reveals that running training can be quite beneficial for young people suffering from various health disorders, including those who have been diagnosed with autism. Research indicates that compared with engaging in mild physical activity, just 15 minutes of steady running by autistic children reduces the frequency of stereotypic behaviors that can interfere with on-task responsiveness.2 Running and other forms of aerobic exercise are believed to be productive tools for the managemen
t of autism in children.3 Positive changes in behavior in response to participation in aerobic running have also been observed in autistic adults.4
Concerns About Injury
While endurance running, conducted in a safe manner with special attention to the risks of heat illness, would appear to be a health-promoting activity for young people, special concerns have been expressed regarding the participation of youngsters in long-distance events such as the marathon. Since a child is not structured proportionally to an adult, a major worry is the possibility of serious injury. Research reveals that the legs account for about 50 percent of an adult’s height but make up less than half of a child’s stature.7 This creates a situation in which a child has relatively less leg to absorb the ground-impact forces associated with running. More impact force can theoretically be transferred to the hips and upper portions of the body.
Young runners can engage in varied training programs with a low risk of injury.
Scientific investigations also indicate that the ratios of contractile muscle strength and static tendon strength to bone length are lower in children than in adults because bone growth tends to precede the development of corresponding muscular and tendon strength. In children, each unit length of leg bone is surrounded and protected by weaker muscles and tendons. This mismatch leaves bones and joints less shielded from injury in children compared with adults, possibly increasing the risk of stress fractures and joint and cartilage maladies in young distance runners.8
A close examination of the possible connection between heavy-duty training and injury in young athletes was completed at the Sports Clinic of the Deaconess Institute of Oulu in Finland. Researchers monitored 48 young track and field athletes over a 3-year period. At the start of the study, 7 were age 10, 3 were 11, 6 were 12, 9 were 13, and 23 others were either 14 or 15; the mean age was 13. Twenty-two of the athletes were girls, and 26 were boys.9
Twenty of the 48 young athletes trained at least six times a week for about 10 hours per week, 23 worked out four or five times weekly for 6 to 10 hours, and 5 trained three times per week for 3 to 6 hours. The training was quite rigorous and produced 39 Finnish Championship medals. Three of the young athletes garnered medals at European Championships.
During the 3-year period of track and field training, there were 41 exercise-related injuries severe enough to curtail training, an unusually low rate of physical difficulty. Expressed in another way, 28 percent of the young athletes were injured during a typical year. Studies of injury rates among adult runners engaged in similar durations of training have detected injury rates of 40 to 65 percent—and as high as 93 percent—per year. Although the exact nature of training is not identical in these inquiries, the research at least suggests that running training is no more harmful in children than it is in adults.
Although a concern remains that children’s injuries might be more damaging in the long term, most of the physical problems that occurred in the Finnish study were slight. In spite of the relatively heavy training loads—over 40 percent of the Finnish youngsters trained more than 10 hours per week—no surgical interventions were necessary, and one-third of the ailments required no special therapies at all. Sixty percent of the training-related injuries healed completely within 2 months, and no lasting injuries were sustained.
One lesson to be learned from the Finnish study may be that variation is an essential part of training for both younger and older runners. The young Finnish athletes did not specialize but instead participated in a number of different track and field events during the 3-year period. Employing a variety of different training techniques involving the development of speed, coordination, technique, strength, and endurance, the young Finns avoided the repetitive pounding of running for long distances. This was much to their advantage since a strong predictor of running-related injury is simply the volume of miles run per week.
A concern has been that endurance running might harm growth plates in children’s bones, but research reveals that long-distance running is not a risk factor for growth-plate problems.10 The American Academy of Pediatrics has concluded that there is no solid reason to preclude marathon running for prepubertal kids as long as their lesser tolerance for heat stress is heeded.11
Female Runners
Despite this generally positive news about running for the younger population, it is nonetheless true that running can sometimes be associated with serious problems when it is carried out in strenuous fashion by young female athletes. Such training can lead to problems with sexual maturation and menstrual cycling as well as difficulties with bone health and disorders related to eating patterns.
Female Athlete Triad
It appears that participation in a rigorous running program at an early age delays sexual maturation in female runners in Great Britain and the United States—and that such late maturers might be more likely to experience amenorrhea in later life. Females who take part in an aggressive running program that delays sexual maturity may increase their risk of stress fractures and osteoporosis especially if their nutritional practices are suboptimal. Science also discloses that young female runners are at a heightened risk for anorexia nervosa.5 Up to 25 percent of female collegiate runners in the United States exhibit significant symptoms of disordered eating.12
It is important to point out that it is not running per se that produces anorexia; rather, the combination of excessive running and inadequate eating is the result of underlying psychological difficulties. The triad of problems encountered in many young female runners—anorexia, osteoporosis, and amenorrhea—is not common in young Kenyan female athletes even though the Kenyan females appear to train more strenuously than their counterparts in the Western world; for example, young Kenyan females ranging in age from 13 to 16 often run about 60 to 70 miles (97-113 km) per week during the cross country season.12 In my observations, the reasons for this may be that young Kenyan females are stronger, in part because of their barefoot, hill-top running at an early age, and that young Kenyans are less likely to attempt to restrict calories intentionally. “Our bodies need a lot of fuel so that we can run well,” young Kenyan female runners often say.
In spite of the prevalence of the athlete triad among female runners, research conducted by Kathleen Pantano revealed that less than half of U.S. Division I collegiate distance-running coaches in the United States are able to identify the three components of the disorder.13 It goes without saying, then, that the majority of college coaches are unable to identify the triad in their female athletes or recommend proper treatment.
Myths about female runners’ responses to strenuous training may make identification of the triad more difficult. Pantano found that 24 percent of coaches believe that absent or irregular menstruation is a normal consequence of training even though dysfunctional menstruation is one of the key aspects of the triad. Triad intervention strategies are most likely to be successful when they include a multidisciplinary team approach.13 Coordination between the coach, a nutritionist, an athletic trainer, and a mental health professional is believed to be the optimal way to help a female athlete avoid the perils of the triad.13
One way to counter the osteoporotic effects of disordered eating and amenorrhea would be to encourage strength training in female runners, particularly those at risk for the athlete triad. Research reveals that regular strength training involving the lower limbs significantly improves mineral density in bones.14 Naturally, such resistance training would not produce optimal effects unless it was undertaken with an appropriate nutritional program that includes increased calories and calcium to support the energy and mineral intake demands of the training.
Pregnancy
Many female runners wonder whether it is all right to continue with running training during pregnancy. Current guidelines in the United States and Europe suggest that pregnant female runners can continue training at a moderate level throughout much of their pregnancy. Running during pregnancy has beneficial effects on many maternal health outcomes, including r
educed risks of preeclampsia15 and gestational diabetes.16 However, the impact of running during pregnancy on the health of the fetus is less clear.17 Running during pregnancy can potentially reduce placental blood flow because of redistribution of blood to the leg muscles and may make the fetus hyperthermic, release hormones that stimulate uterine contractility, and promote fetal hypoglycemia because the leg muscles rob the fetus of glucose during intense or prolonged runs.
Research in this area has been inconclusive. Three studies have found no link at all between exercise during pregnancy and miscarriage,18-20 and one inquiry actually found that regular exercise protected against miscarriage.21 However, a recent Danish investigation carried out with 92,671 pregnant women detected a stepwise, increasing relationship between exercise and the risk of miscarriage.22 For example, according to this study, women who exercised more than 7 hours per week had an almost fourfold increase in the risk of miscarriage. However, running and other exercise was not connected with an increased chance of miscarriage beyond 18 weeks of gestation. It is clear that female runners who are pregnant should consult closely with their physicians.
Running Science Page 58