Wednesday, May 26, 2010
For the body and the mind.
At Jungle Miami, we like to share articles that we think are key to being fit and healthy. Today, we are posting two pieces on the benefits of exercising. They are not just for the body but also for the mind. They are also not just for adults but for kids, too. We hope you will enjoy them and can learn something new that serves you well.
-"Lobes of Steel".
Gretchen Reynolds, August, 19, 2007. New York Times.
The Morris water maze is the rodent equivalent of an I.Q. test: mice are placed in a tank filled with water dyed an opaque color. Beneath a small area of the surface is a platform, which the mice can’t see. Despite what you’ve heard about rodents and sinking ships, mice hate water; those that blunder upon the platform climb onto it immediately. Scientists have long agreed that a mouse’s spatial memory can be inferred by how quickly the animal finds its way in subsequent dunkings. A “smart” mouse remembers the platform and swims right to it.
In the late 1990s, one group of mice at the Salk Institute for Biological Studies, near San Diego, blew away the others in the Morris maze. The difference between the smart mice and those that floundered? Exercise. The brainy mice had running wheels in their cages, and the others didn’t.
Scientists have suspected for decades that exercise, particularly regular aerobic exercise, can affect the brain. But they could only speculate as to how. Now an expanding body of research shows that exercise can improve the performance of the brain by boosting memory and cognitive processing speed. Exercise can, in fact, create a stronger, faster brain.
This theory emerged from those mouse studies at the Salk Institute. After conducting maze tests, the neuroscientist Fred H. Gage and his colleagues examined brain samples from the mice. Conventional wisdom had long held that animal (and human) brains weren’t malleable: after a brief window early in life, the brain could no longer grow or renew itself. The supply of neurons — the brain cells that enable us to think — was believed to be fixed almost from birth. As the cells died through aging, mental function declined. The damage couldn’t be staved off or repaired.
Gage’s mice proved otherwise. Before being euthanized, the animals had been injected with a chemical compound that incorporates itself into actively dividing cells. During autopsy, those cells could be identified by using a dye. Gage and his team presumed they wouldn’t find such cells in the mice’s brain tissue, but to their astonishment, they did. Up until the point of death, the mice were creating fresh neurons. Their brains were regenerating themselves.
All of the mice showed this vivid proof of what’s known as “neurogenesis,” or the creation of new neurons. But the brains of the athletic mice in particular showed many more. These mice, the ones that scampered on running wheels, were producing two to three times as many new neurons as the mice that didn’t exercise.
But did neurogenesis also happen in the human brain? To find out, Gage and his colleagues had obtained brain tissue from deceased cancer patients who had donated their bodies to research. While still living, these people were injected with the same type of compound used on Gage’s mice. (Pathologists were hoping to learn more about how quickly the patients’ tumor cells were growing.) When Gage dyed their brain samples, he again saw new neurons. Like the mice, the humans showed evidence of neurogenesis.
Gage’s discovery hit the world of neurological research like a thunderclap. Since then, scientists have been finding more evidence that the human brain is not only capable of renewing itself but that exercise speeds the process.
“We’ve always known that our brains control our behavior,” Gage says, “but not that our behavior could control and change the structure of our brains.”
The human brain is extremely difficult to study, especially when a person is still alive. Without euthanizing their subjects, the closest that researchers can get to seeing what goes on in there is through a functional M.R.I. machine, which measures the size and shape of the brain and, unlike a standard M.R.I. machine, tracks blood flow and electrical activity.
This spring, neuroscientists at Columbia University in New York City published a study in which a group of men and women, ranging in age from 21 to 45, began working out for one hour four times a week. After 12 weeks, the test subjects, predictably, became more fit. Their VO2 max, the standard measure of how much oxygen a person takes in while exercising, rose significantly.
But something else happened as a result of all those workouts: blood flowed at a much higher volume to a part of the brain responsible for neurogenesis. Functional M.R.I.’s showed that a portion of each person’s hippocampus received almost twice the blood volume as it did before. Scientists suspect that the blood pumping into that part of the brain was helping to produce fresh neurons.
The hippocampus plays a large role in how mammals create and process memories; it also plays a role in cognition. If your hippocampus is damaged, you most likely have trouble learning facts and forming new memories. Age plays a factor, too. As you get older, your brain gets smaller, and one of the areas most prone to this shrinkage is the hippocampus. (This can start depressingly early, in your 30’s.) Many neurologists believe that the loss of neurons in the hippocampus may be a primary cause of the cognitive decay associated with aging. A number of studies have shown that people with Alzheimer’s and other forms of dementia tend to have smaller-than-normal hippocampi.
The Columbia study suggests that shrinkage to parts of the hippocampus can be slowed via exercise. The subjects showed significant improvements in memory, as measured by a word-recall test. Those with the biggest increases in VO2 max had the best scores of all.
“It’s reasonable to infer, though we’re not yet certain, that neurogenesis was happening in the people’s hippocampi,” says Scott A. Small, an associate professor of neurology at Columbia and the senior author of the study, “and that working out was driving the neurogenesis.”
Other recent studies support this theory. At the University of Illinois at Urbana- Champaign, a group of elderly sedentary people were assigned to either an aerobic exercise program or a regimen of stretching. (The aerobic group walked for at least one hour three times a week.) After six months, their brains were scanned using an M.R.I. Those who had been doing aerobic exercise showed significant growth in several areas of the brain. These results raise the hope that the human brain has the capacity not only to produce new cells but also to add new blood vessels and strengthen neural connections, allowing young neurons to integrate themselves into the wider neural network. “The current findings are the first, to our knowledge, to confirm the benefits of exercise training on brain volume in aging humans,” the authors concluded.
And the benefits aren’t limited to adults. Other University of Illinois scientists have studied school-age children and found that those who have a higher level of aerobic fitness processed information more efficiently; they were quicker on a battery of computerized flashcard tests. The researchers also found that higher levels of aerobic fitness corresponded to better standardized test scores among a set of Illinois public school students. The scientists next plan to study how students’ scores change as their fitness improves.
What is it about exercise that prompts the brain to remake itself? Different scientists have pet theories. One popular hypothesis credits insulin-like growth factor 1, a protein that circulates in the blood and is produced in greater amounts in response to exercise. IGF-1 has trouble entering the brain — it stops at what’s called the “blood-brain barrier” — but exercise is thought to help it to do so, possibly sparking neurogenesis.
Other researchers are looking at the role of serotonin, a hormone that influences mood. Exercise speeds the brain’s production of serotonin, which could, in turn, prompt new neurons to grow. Abnormally low levels of serotonin have been associated with clinical depression, as has a strikingly shrunken hippocampus. Many antidepressant medications, like Prozac, increase the effectiveness of serotonin. Interestingly, these drugs take three to four weeks to begin working — about the same time required for new neurons to form and mature. Part of the reason these drugs are effective, then, could be that they’re increasing neurogenesis. “Just as exercise does,”Gage says.
Gage, by the way, exercises just about every day, as do most colleagues in his field. Scott Small at Columbia, for instance , likes nothing better than a strenuous game of tennis. “As a neurologist,” he explains, “I constantly get asked at cocktail parties what someone can do to protect their mental functioning. I tell them, ‘Put down that glass and go for a run.
"This Is Your Brain on Something Other Than Exercise" The human brain undergoes neurogenesis — the creation of new cells — throughout a person’s life, although the amount depends on a variety of factors, not just exercise.
MARIJUANA: We just report the data; we don’t endorse it. A 2005 study on rats found that stimulation of the brain’s receptors for marijuana increased neurogenesis.
ALCOHOL: A 2005 study found that mice that swallowed a moderate amount of ethanol showed more neurogenesis than teetotalers. Other studies on mice have suggested that heavier drinking can be damaging to the brain.
SOCIABILITY: One study suggests that rats that live alone and have access to a run ning wheel experience less neurogenesis than those that have access to a running wheel and live in group housing. So go ahead and join that singles running club you’ve been avoiding.
DIET: A diet high in saturated fat and sugar sharply diminishes the brain’s production of the proteins and nerve-growth factors necessary for neurogenesis. Exercise may mitigate that effect somewhat.
STRESS: Mice that are subjected to uncontrollable stress (like electric shock) suffer substantial deterioration in their ability to produce new neurons.
CHOCOLATE: In a study published this year, an ingredient in cocoa, epicatechin, was shown to improve spatial memory in mice, especially among those that exercised. Epicatechin can also be found in grapes, blueberries and black tea. “I plan to start ingesting more epicatechin,” says Henriette van Praag, a neuroscientist at the Salk Institute, “as soon as I can’t find my car keys anymore.” G.R.
"A Little Counseling Can Pay Lasting Dividends"
Theodore Ganley, MD, with Carl Sherman
Exercise Is Medicine series editor: Nicholas A. DiNubile, MD
THE PHYSICIAN AND SPORTSMEDICINE - VOL 28 - NO. 2 - FEBRUARY 2000
In Brief: Regular exercise is an important health maintenance strategy for children and adolescents: It facilitates weight control, helps strengthen bones, and can improve cardiovascular risk factors. Mental health may also benefit. An active childhood may also lay the groundwork for a lifetime of fitness. Physicians are in an important position to assess children's weight status and activity levels during a routine physical exam. And, with some simple recommendations to children and parents, they can play a key role in helping young patients find and maintain activities they enjoy, while keeping the risk of injury to a minimum.
Every child and adolescent needs exercise. It is a sound and largely risk-free investment in their present and future health. Physicians who care for young patients should take an active role in helping them choose and maintain activities appropriate to their age, physical condition, stage of development, and interests.
Ignoring health promotion in young people may reflect two beliefs: (1) that though inactivity is widespread in adults, children are naturally and spontaneously active, and (2) that the health risks associated with a sedentary lifestyle such as diabetes and heart disease are far more pressing in adults.
Ample evidence, however, documents that young people are not the dependably kinetic creatures of popular imagination. Fewer than half of US children engage in activity sufficient for cardiovascular benefit and long-term health promotion (1). According to the surgeon general's report on physical activity and health (2), activity levels decline as grade levels advance--dramatically so as children enter adolescence. Nearly half of US young people ages 12 to 21 are not regularly vigorously active. One-fourth engage in no vigorous activity, and 14% report no recent activity at even the light-to-moderate level. Girls are at greater risk of inactivity than boys, particularly during and after puberty.
These trends have not been reversed with physical education. Just over one third of elementary and secondary schools offer daily physical education classes (1). High school enrollment in such classes has declined in recent years, from 42% in 1991 to 25% in 1995 (2).
How Exercise Improves Kids' Health.
This decline is not without cost: A sedentary lifestyle in young people can have negative health consequences both now and later.
Weight control. According to a recent statistical analysis (3), nearly one fourth of American children were overweight in 1991, up 20% from 1981. The relationship between physical activity and adiposity in children is complex, especially at earlier ages, and studies have been inconsistent (4). But increasing physical activity while restricting calorie intake has been documented as an effective weight loss strategy (5). The need for obesity interventions is clear. Overweight children are at increased risk of many health problems, including hypertension, hyperlipidemia, type 2 diabetes, growth hormone dysregulation, and respiratory and orthopedic problems. Self-esteem and socialization frequently suffer (6). And that is just the beginning. Not only does obesity follow children into adulthood--40% of overweight children and 70% of overweight adolescents become obese adults--obesity in adolescence is independently associated with chronic diseases that develop in adulthood (7). For information on evaluating children for obesity, see "Weight Assessment in Children and Adolescents," below.
Bone building. Physical activity in childhood may have lasting effects on bone development. Exercise may lower osteoporosis risk by increasing bone mineral density. Though most attention has focused on exercise in later years to reduce or restore bone loss, the skeleton appears to be most responsive to the effects of activity during growth (see "Osteoporosis: Understanding Key Risk Factors and Therapeutic Options") (8). Evidence for a positive effect of childhood activity on bone density, either immediately or later in life, is mixed, but a number of studies have this implication. One followed 40 prepubertal boys (mean age, 10.4 years), half of whom participated in 30 minutes of weight-bearing exercise three times a week for 32 weeks (9). The increase in lumbar spine, leg, and total body bone mineral density was twice as great in the exercise group as in controls.
Another study (10) that involved 45 prepubertal female gymnasts (mean age, 10.4 years), 36 retired gymnasts (mean age, 25 years), and 50 matched controls found significantly greater bone mineral density in the young and retired gymnasts. The researchers observed that bone density did not diminish during retirement, despite the lower frequency and intensity of exercise. They concluded that exercise before puberty may reduce fracture risk after menopause.
Cardiovascular protection. While cardiovascular disease is primarily manifested in adulthood, risk factors appear much earlier in life and typically persist. Evidence links lipid and lipoprotein profiles in childhood and adolescence with the development of atherosclerotic lesions (11) and high-normal blood pressure in young people. These conditions significantly increase the risk of essential hypertension in adulthood (12). A substantial body of research documents the positive effect of physical activity, particularly at aerobic levels, on cardiovascular risk factors in adults, but the evidence for children is more limited and equivocal (4). Nevertheless, some well-designed studies (13,14) suggest that aerobic exercise is beneficial in this age-group, particularly for individuals at high risk. One trial (13) compared 28 prepubertal children who took part in a 12-week exercise program (stationary cycling for 30 minutes, three times per week) with 20 controls who did not. The exercise groups had significant improvement in low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, and the total cholesterol/HDL and LDL/HDL ratios.
Another study (14) found positive effects on blood pressure. Ninety-nine ninth-grade girls whose systolic or diastolic blood pressure was in the top third for their grade were randomized to a semester of aerobic exercise or standard physical education (PE) classes. Among the 88 who completed the study, systolic blood pressure dropped significantly more in the aerobic exercise group than in the standard PE group (6 mm Hg versus 3.7 mm Hg). Though decreases were modest, the blood pressure reduction was notable, considering that the girls were not hypertensive. The authors concluded that changes of this magnitude, if widely achieved, could have important public health benefits and observed that similar reductions have been seen in other trials of physical training in adolescents.
Mental health benefits. That exercise has a beneficial effect on mental health for children as well as adults is an attractive, intuitive, and widely held notion. For example, one review (15) states that most studies, which have primarily involved adults, have documented improvements in depressive and anxiety symptoms. However, in areas such as self-concept, hard data are scarce. Some studies suggest that the positive effect of exercise is limited and that exercise improves children's physical self-image but not academic or general self-worth (16). Sports participation has not been shown to foster moral development, which appears to depend on the specific context and conditions such as role models and leadership(17). Exercise may improve the ability of young people to cope with stress. A study (18) of 220 adolescent girls during a high-stress period found that those who adhered to a rigorous exercise program reported less physical and emotional distress than those who exercised less.
Does Activity Follow Into Adulthood?
It would be gratifying to report that early exercise patterns continue into adulthood. While this seems intuitively so, supporting data have been limited and reflect the fallibility of recall and the difficulty of following individuals from preteen years to adulthood.
One recent study (19) compared 174 men and women who had five PE sessions per week in the 6 years of elementary school (in the early 1970s) with a control group of 720 who had less frequent PE. When surveyed in the mid 1990s, women, but not men, in the high-frequency PE group reported more frequent physical activity than controls. Men who had more frequent PE as children, however, were significantly less likely to smoke than controls (11.3% vs 30.8%).
Another study (20) suggested that childhood exercise, if promoted unwisely, can impede adult physical activity. An analysis of the preteen and teenage experience of 105 middle-age men found that coercion to exercise in youth had a weak but statistically significant negative effect on physical activity in adulthood. The authors noted that the results seem to emphasize the need to give children a voice in their physical activity and sports participation.
Tailoring the Program
In sum, the lesson for physicians seems to be: Promote exercise in young patients, but do it positively and realize that activities must be individualized for each child (See the Patient Adviser, "Channel Kids' Energy Toward Exercise"). In light of the prevalence of sedentary behavior and its potential health consequences, a discussion of physical activity should be part of every exam. The issue deserves the same kind of attention as counseling on smoking and other aspects of health maintenance.
Exercise promotion is particularly important when working with girls or minority or low-income youth (21), who, for many reasons, have been shown to have more sedentary lifestyles. Children who have disabilities are generally less fit than those who are able-bodied; ironically, they probably need higher fitness levels to improve their function later in life. Except for that promoted by organizations such as the Special Olympics, exercise opportunities are few for children who have disabilities, and individuals, schools, and communities should do more to foster sports and recreation programs for them.
Obtaining an activity inventory can help physicians more fully understand patients' activities and energy expenditure. It can also help physicians suggest activities that are most appropriate for children's age, size, abilities, interests, and medical conditions.
Questions may be asked about:
• Physical education, including the frequency of classes and types of activities;
• Aerobic activities such as running and soccer versus relatively nonaerobic activities such as baseball;
• Sedentary activity, including time spent with computers, video games, and television; and
• Recreational and other physical activities such as snowboarding, in-line skating, hiking, and working at a physically demanding job.
No single sport or exercise regimen is uniquely beneficial for the physical or emotional well-being of children. It is far more important to find, with the help of parents, activities that will be interesting and enjoyable for the child and are appropriate to his or her age and physical abilities (see "Which Sports When?" below).
Though it is not necessary to exercise at anything approaching maximum capacity, aerobic activities are ideal. A reasonable goal, as suggested by the recent surgeon general's report on health and physical activity (2), is 30 minutes of moderate activity on most days of the week. Greater daily activity such as walking or climbing stairs also contributes to overall fitness and well-being. Strength training has grown in popularity, and even prepubescent children can achieve measurable gains with little risk of injury and no adverse effect on bone, muscle, or joint development (22). Adequate supervision is essential, however, with emphasis placed on correct form and technique. Children should not lift maximum weights and should avoid ballistic movements until skeletal growth is completed.
In some cases, physicians may steer children toward exercises that are appropriate to their strengths and vulnerabilities. Patients with ligamentous laxity, for example, might be encouraged to swim or bicycle rather than play sports such as basketball that involve pivoting and twisting. Times of rapid growth often increase vulnerability to certain injuries, and a temporary switch to low-impact activities can prevent injury during these times.
Minimizing Injury Risk
Safety is paramount. Though exercise-related mishaps are common--one study (23) found that 22% of school-aged children sustained injury during physical education class or in outside sports each year--most injuries are minor. A prudent approach will minimize overuse injuries and more serious trauma.
For example, parents should assess whether organized sports are conducted with appropriate attention to safety and injury prevention. Little League, for example, uses pitch counts to avoid overuse injuries; Pop Warner football divides players into leagues based on age and weight. While there is nothing wrong with competition, children should not be encouraged to push themselves to the point at which injuries are more likely.
Children should not play when in pain or take painkillers to participate. Coaches and parents should be alert to signs that an overuse injury may be developing, such as limping on the field or rubbing of the arm after throwing.
In general, sensible precautions will minimize risk. Children should use appropriate equipment for each sport, including footwear that provides appropriate support and traction. Bicycle helmets are a must. Play areas should be free of debris, ruts, and divots.
Stretching and warm-up to minimize hamstring pulls and similar injuries should become habitual preludes to strenuous exercise. Children's bones often grow at a faster rate than adjacent muscles and tendons. Physes also grow at different rates. Seventy percent of the growth of the lower extremities occurs at the physes at the knees. These factors predispose children and adolescents to muscle tightness, especially at the hamstrings and quadriceps.
Don't overlook the obvious. The most common, severe, recreation-related injuries to children are caused by motor vehicles. Play areas should be away from traffic, and safe practices emphasized for walking and biking. The risk of injury when traveling to or from organized or casual play areas is far higher than the risk of play itself.
Counsel about sun and heat protection. Children, like adults, should wear sunscreen when exercising outside. To avoid dehydration, to which children's smaller size makes them more vulnerable, they should be taught to drink fluids before and after exercise and during activity that lasts longer than 20 to 30 minutes--without waiting until they are thirsty. Though carbohydrate-electrolyte sports drinks may have no special merit, they may enhance voluntary drinking because of their taste or ability to induce thirst (24).
The goal--safe, enjoyable exercise--is readily attainable by virtually all youngsters. In children's exercise, a relatively modest amount of physician counseling will likely pay lasting dividends.
1. DiNubile NA: Youth fitness: problems and solutions. Prev Med 1993;22(4):589-594
2. US Department of Health and Human Services: Physical Activity and Health: A Report of the Surgeon General. Atlanta, DHHS, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, 1996
3. Troiano RP, Felgal KM, Kuczmarski RJ, et al: Overweight prevalence and trends for children and adolescents: the National Health and Nutrition Examination Surveys, 1963 to 1991. Arch Pediatr Adolesc Med 1995;149(10):1085-1091
4. Caspersen CJ, Nixon PA, DuRant RH: Physical activity epidemiology applied to children and adolescents. Exerc Sport Sci Rev 1998;26:341-403
5. Bar-Or O, Baranowski T: Physical activity, adiposity, and obesity among adolescents. Pediatr Ex Sci 1994;6:348-360
6. Bar-Or O, Foreyt J, Bouchard C, et al: Physical activity, genetic, and nutritional considerations in childhood weight management. Med Sci Sport Exerc 1998;30(1):2-10
7. Must A, Jacques PF, Dallal GE, et al: Long-term morbidity and mortality of overweight adolescents: a follow-up of the Harvard Growth Study. N Engl J Med 1992;327(19):1350-1355
8. Welten DC, Kemper HC, Post GB, et al: Weight-bearing activity during youth is a more important factor for peak bone mass than calcium intake. J Bone Miner Res 1994;9(7):1089-1096
9. Bradney M, Pearce G, Naughton G, et al: Moderate exercise during growth in prepubertal boys: changes in bone mass, size, volumetric density and bone strength: a controlled prospective study. J Bone Miner Res 1998;13(12):1814-1821
10. Bass S, Pearce G, Bradney M, et al: Exercise before puberty may confer residual benefits in bone density in adulthood: studies in active prepubertal and retired female gymnasts. J Bone Miner Res 1998;13(3):500-507
11. Newman WP III, Wattigney W, Berenson GS: Autopsy studies of United States children and adolescents: relationships of risk factors to arteriosclerotic lesions. Ann NY Acad Sci 1991;623:16-25
12. The fifth report of the Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure. Arch Intern Med 1993;153(2):154-183
13. Tolfrey K, Campbell IG, Batterham AM: Exercise training induced alterations in prepubertal children's lipid-lipoprotein profile. Med Sci Sports Exerc 1998;30(12):1684-1692
14. Ewart CK, Young DR, Hagberg JM: Effects of school-based aerobic exercise on blood pressure in adolescent girls at risk for hypertension. Am J Public Health 1998;88(6):949-951
15. Byrne A, Byrne DG: The effect of exercise on depression, anxiety and other mood states: a review. J Psychosom Res 1993;37(6):565-574
16. Biddle S: Children, exercise and mental health. Int J Sports Psychol 1993;24:200-216
17. President's Council on Physical Fitness and Sport: Physical Activity & Sport in the Lives of Girls. Washington, DC, US Department of Human Services, 1998
18. Brown JD, Lawton M: Stress and well-being in adolescence: the moderating role of physical exercise. J Hum Stress 1986;12(3):125-131
19. Trudeau F, Laurencelle L, Tremblay J, et al: Daily primary school physical education: effects on physical activity during adult life. Med Sci Sports Exerc 1999;31(1):111-117
20. Taylor WC, Blair SN, Cummings SS, et al: Childhood and adolescent physical activity patterns and adult physical activity. Med Sci Sports Exerc 1999;31(1):118-123
21. Taylor WC, Baranowski T, Young DR: Physical activity interventions in low-income, ethnic minority, and populations with disability. Am J Preventive Med 1998;14(4):334-343
22. Rians CB, Weltman A, Cahill BR, et al: Strength training for prepubescent males: is it safe? Am J Sports Med 1987;15(5):483-489
23. Maffulli N, Baxter-Jones AD: Common skeletal injuries in young athletes. Sports Med 1995;19(2):137-149
24. Rivera-Brown AM, Gutierrez R, Gutierrez JC, et al: Drink composition, voluntary drinking, and fluid balance in exercising, trained, heat-acclimatized boys. J Appl Physiol 1999;86(1):78-84
Weight Assessment in Children and Adolescents
Physical activity can help patients of all ages achieve body proportions that are suited to their height and frame. Being overweight is not a normal part of child physical development. However, it is important for patients to understand that there is a wide range of body types and that some body types are genetically determined.
Obesity definitions or standards have not been clearly established for children and adolescents (1). However, body mass index (BMI, measured in kg/m2) can be used to evaluate obesity in this age-group. In adolescents, BMI has been found to be highly specific but variably sensitive (2). Suggested thresholds for obesity vary between the 85th and 95th BMI percentiles.
Though the BMI is a noninvasive and general estimate of a patient's percent body fat, it is important to consider factors such as race, sex, sexual maturation, and body-fat distribution when interpreting the results. BMI should be considered a screening tool, and patients identified as obese or at risk of becoming obese should be referred for counseling (2).
BMI in athletic patients can be misleading. Elite athletes may have a higher BMI because they have a greater lean body mass or bone mass that skews the results. In these patients, skinfold testing should be used with the BMI to assess their body fat.
The US national growth charts for infants and children up to age 18 were drafted in 1977. Since then, the charts are being revised to reflect demographic changes and the increased prevalence of obesity (3). The use of BMI for age, instead of a strict height-for-weight measurement, has also been incorporated into the revised growth charts.
How Much Weight to Put on Weight?
Though it is important to assess weight in young patients, physicians should not dwell on body habitus. Weight evaluation is primarily useful for diet and exercise counseling and screening for underlying medical conditions such as hypothyroidism, Prader-Willi syndrome, and the effects of medications such as corticosteroids.
Just as obesity has its own set of health risks, being significantly underweight and obsessed with one's body habitus can be equally, if not more, detrimental to health and well being: Dangerous eating disorders such as anorexia nervosa may be the result (4). These patients may most benefit by hearing reassurance of their self-worth. When discussing exercise with these young people, it is helpful to emphasize fitness benefits rather than appearance benefits.
1. Berkowitz RI: Obesity in childhood and adolescence, in Walker WA, Watkins JB (eds): Nutrition in Pediatrics: Basic Science and Clinical Applications, ed 2. Malden, MA, Blackwell Science, 1997, pp 716-723
2. Malina RM, Katzmarzyk PT: Validity of the body mass index as an indicator of the risk and presence of overweight in adolescents. Am J Clin Nutr 1999;70(suppl):131S-136S
3. Guo SS, Roche AF, Moore WM: The revised US National Growth Charts. Nutrition & the MD 1999;25:1-4
4. Yeager KK, Agostini R, Nattiv A, et al: The female athlete triad: disordered eating, amenorrhea, osteoporosis. Med Sci Sports Exerc 1993;25(7): 775-777
Which Sports When?
Though exercise is good for all children, every activity isn't suitable for every child. One question that often comes up in discussions with parents is age: When is the child ready for distance running (or skiing, or weight training)?
"It's a matching game," says Steven J. Anderson, MD, clinical professor in the Department of Pediatrics at the University of Washington in Seattle and chair of the American Academy of Pediatrics (AAP) Committee on Sports Medicine and Fitness. "The idea is to match the demands of the sport or exercise activity to the developmental maturity of the child."
Motor and Cognitive Readiness
Readiness issues are clearest in motor development, according to Sally Harris, MD, MPH, a pediatrician in the Department of Sports Medicine at the Palo Alto Medical Foundation in Palo Alto, California, and pediatric chair of the AAP Section on Sports Medicine and Fitness. Skills relevant to sports, such as throwing and kicking, can't be rushed any more than developmental milestones like rolling over or sitting up. "If the child doesn't have them, the sport will be a frustrating experience."
Less obvious but also important are the cognitive and social capacities that enable the child to interact with teammates, visualize their place on a team, and understand strategy. "In these areas, adults forget that children are not as mature as they are," Harris says.
Because the pace of development varies widely, it's impossible to specify sports-readiness ages with precision. "We go mostly by common sense and experience," Harris says. But she does suggest some general guidelines for the following age-groups:
• 2 to 5 years. Children are just learning fundamental skills like throwing, catching, running, and jumping. It's best to stick with activities that use these skills but don't combine them in a complicated way.
• 6 to 9 years. Children put the fundamentals together in moves related to actual sports: throwing for distance or accuracy; rearing back to kick a ball. Better memory and decision-making enable them to deal with basic strategies of simplified forms of baseball or soccer.
• 10 to 12 years. Youngsters can master the complex motor skills they need and have the cognitive ability to learn strategies for "adult" forms of most sports, including football and basketball.
Readiness for competition is controversial (1). "Competitive sports for preschool-age kids is frowned upon," Anderson says. "Even in early elementary school, the emphasis should be on learning basic skills and rules, without the added pressure of competition." Equal participation rather than winning should be the goal at this age.
Injury prevention is a legitimate concern but rarely an age-limiting factor. "People worry about intensive training for young children, but that's not the time of highest risk," Harris says. Overuse and traumatic injuries are actually more common during and after puberty, as size, strength, and growth rate increase. The AAP discourages headfirst sliding in baseball for children under age 10 (2), for example. The risk of injury may actually be greater for adolescents, however, because they are heavier and faster than their younger counterparts.
In general, rule modifications and special equipment have widened the sports activity options for children, and "readiness" often comes down to motivation: the point at which participation reflects the child's real interest, as opposed to adult or peer pressure. In conversations with children and parents, questions often arise about the demands of specific sports.
Soccer. Children can kick the ball by age 6 or 8 but can't fully grasp concepts of player positioning, passing, and making plays until several years later. The result: "beehive soccer," a popular adaptation in which they swarm around the ball without much concern for adult rules.
Baseball. Most 6-year-old children lack the eye-hand coordination to hit a pitched ball but can play "tee-ball," swinging at the ball on a tee. Bigger bats and balls, smaller fields, and more fielders also make the game more fun at this age. For children under 12 in organized leagues, "pitch count" guidelines (eg, limiting pitchers to 6 innings per week, or 2 days rest for every 30 pitches thrown) reduce the risk of overuse injury.
Running. Distance running doesn't seem to harm young joints or growth plates, and there's no reason to preclude even marathoning for prepubertal children (3). Children do, however, have less tolerance for heat stress, so adequate hydration before, during, and after running is essential. The same applies to triathlons if they are specifically designed for the age-group. However, the emphasis should be on fun and fitness rather than competition (4).
Strength training. Using free weights and machines to increase strength appears to pose no great risk of injury, even to prepubertal youngsters (5). However, the activity should be well supervised, and children should not attempt maximal weight--the most they can lift just one time--before skeletal maturity (Tanner stage 5--typically at age 15 in girls and age 17 in boys). Before that point, they should likewise avoid ballistic maneuvers such as Olympic-style weight lifting (a single-repetition maximum lift in two stages: the snatch and the clean and jerk) power lifting (three separate maximum lifts), and bodybuilding (6).
Skiing. Cross-country skiing of reasonable distances is adaptable for children who are adept at walking and running. Downhill skiing can similarly be enjoyed by those as young as age 3 or 4, particularly with modifications and special equipment such as connectors to keep the skis in a permanent snowplow position, and harnesses and tethers to let parents control the young skier.
1. Passer MW: Psychological issues in determining children's age-readiness for competition, in Smoll FL, Magill RA, Ash MJ (eds): Children In Sport, ed 3. Champaign, IL, Human Kinetics, 1988, pp 67-77
2. American Academy of Pediatrics: Risk of injury from baseball and softball in children 5 to 14 years of age. Pediatrics 1994;93(4):690-692
3. American Academy of Pediatrics: Risks in distance running for children. Pediatrics 1990;86(5):799-800
4. American Academy of Pediatrics: Triathlon competition by children and adolescents. Pediatrics 1996;98(3):511-512
5. Blimkie CJR: Benefits and risks of resistance training in children, in Cahill BR, Pearl AJ (eds): Intensive Participation in Children's Sports. Champaign IL, Human Kinetics, 1993, pp 133-165
6. American Academy of Pediatrics: Strength training, weight and power lifting, and body building by children and adolescents. Pediatrics 1990;86(5):801-803
Dr Ganley is orthopedic director of sports medicine at the Children's Hospital of Philadelphia. Mr Sherman is a freelance writer in New York City. Address correspondence to Theodore Ganley, MD, Children's Hospital of Philadelphia, Dept of Orthopedic Surgery, 2nd Floor, Wood Bldg, 34th St and Civic Center Blvd, Philadelphia, PA 19104.