THE PHYSICIAN AND SPORTSMEDICINE - VOL 29 - NO. 2 - FEBRUARY 2001

Sports Training and Growth Delay

Is There a Connection?

Concern over possible growth-stunting effects of competitive sports has been heightened in recent years by the image of the pixieish female gymnast, who seems to be getting smaller with each Olympic Games. But interest extends to other sports settings, such as soccer and swimming, in which boys and girls seem to be practicing and competing at higher intensities.

New Evidence on Sports and Prepubertal Growth

Is childhood growth affected by sport? The question gets complex when examining the many factors such as nutrition and genetics that influence growth and the impact of training during different stages of childhood. Research has yet to provide clear answers, and controversy is brewing in the auxology (the study of growth) community, particularly regarding the effects of sport training on the growth of girls.

A report by Danish researchers (1) recently brought the controversies to the forefront with findings that prepubertal growth is not affected by training. Their report also explored the potential influences of genetics, birth weight, early childhood growth, and pubertal status on growth.

A total of 184 children (96 girls and 88 boys) who competed in swimming, tennis, team handball, and gymnastics were assessed for height, weight, pubertal development, and body mass index (BMI). Of the participants, 137 (76 girls and 61 boys) returned a questionnaire that allowed researchers to determine height and BMI between ages 2 and 4, birth weight, and parental heights.

Although no correlation was found between hours spent training and growth, several other patterns emerged suggesting that other factors—genetics, size attained before starting the sport, and pubertal status (in boys)—did relate to growth as reflected by the children's current height and BMI. Notable findings included:

• Prepubertal and early pubertal children who engage in moderate amounts of exercise (less than 10 hours per week) appear to be at minimal risk of attenuated growth and maturation.
• Female gymnasts were shorter than girls in other sports; however, they were shorter even before starting gymnastics, suggesting that children choose sports that are suitable to their size.
• Female tennis players, but not male tennis players, had taller parents than girls participating in other sports, suggesting that a different set of factors may govern selection and sorting in girls and boys sports.
• Male gymnasts trained significantly more than participants in other sports.

The researchers note that their study does not rule out a negative effect of training at later stages of development and that most of their athletes trained less than the 15- to 18-hour-per-week limit suggested to avoid possible growth stunting in gymnasts (2).

Findings Stir Controversy

Dennis Caine, PhD, professor in the Department of Physical Education, Health, and Recreation at Western Washington University in Bellingham, says that two camps appear to be forming among growth researchers: those who maintain that no viable evidence supports an adverse effect of sports training on growth and those who argue that observations of catch-up growth observed after reducing or stopping training provides compelling evidence that growth is affected. Shona Bass, PhD, senior lecturer in the School of Health Sciences at Deakin University in Melbourne, Australia, adds that the controversy is fueled by the difficulty discerning normal temporal growth patterns from exercise or other factors that might influence growth.

When readers analyze reports that assess the influence of sports activity on growth, Caine advises them to keep in mind that a host of other factors associated with sports participation may adversely affect growth and maturation. These include training volume and intensity, nutritional state, energy expenditure, psychological and emotional stress, and physeal injury. Bass adds that determining the effects of sports training on growth is further complicated by varied training and competition across sports and individual responses to those demands.

The strength of the Danish study, Caine says, is that it highlights the importance of constitutional factors that influence selection and sorting in sports such as gymnastics. The report confirms previous findings (3,4) that top-level gymnasts are shorter than young athletes in other sports long before selection.

Caine says that one shortcoming of the current study, as with previous studies on growth and sports, is that the incidence of inadequate growth was not determined. He believes that the researchers' evidence suggesting no adverse effect on growth is weak because comparing data from two age periods may obscure growth patterns of individual athletes.

As the researchers acknowledge, Caine agrees that the risk of reduced growth would be greater during the peripubertal period, "given the increased energy requirements associated with accelerated growth and increased levels of training, as well as perhaps the increased tendency to restrict diet."

Clinical Implications

Bass and Caine have several practical tips for physicians that are based on current research findings:

• Monitor growth and maturation in children who are in elite sports programs, particularly those who restrict their diets and/or are involved in sports in which leanness is important. Before puberty, start plotting the growth of these children regularly on a standard growth chart.
• Perform a complete physical evaluation if height or weight deviate from the predicted growth curve.
• Be aware of a child's training intensity as well as the training volume (hours). There is little evidence in the medical literature to use a 15- to 18-hour threshold.
• Consider a child's individual response to training and competition.

Future Research Directions

Bass led a research team that in 2000 published a report (5) showing delayed growth in peripubertal gymnasts. Bass says that the direction of future research on growth and maturation should answer evolving questions such as the effect of exercise on trunk growth versus leg growth. "The absence of the adolescent growth spurt in my study was due to reduced growth in the trunk, not the legs," she says.

Also, researchers should try to clarify the effects of exercise on bone age versus sexual maturation. "Each reflects different endocrine regulation," she notes. Another research goal is to determine the role of catch-up growth after a young athlete reduces or stops training.

Lisa Schnirring
Minneapolis

REFERENCES

1. Damsgaard R, Bencke J, Matthiesen G, et al: Is prepubertal growth adversely affected by sport? Med Sci Sports Exerc 2000;32(10):1698-1703
2. Theintz GE, Howard H, Weiss U, et al: Evidence for a reduction of growth potential in adolescent female gymnasts. J Pediatr 1993;122(2):306-313
3. Peltenburg AL, Erich WB, Zonderland ML, et al: A retrospective growth study of female gymnasts and girl swimmers. Int J Sports Med 1984;5(5):262-267
4. Daly RM, Rich PA, Klein R, et al: Short stature in competitive prepubertal and early pubertal male gymnasts: the result of selection bias or intense training? J Pediatr 2000;137(4):510-516
5. 5. Bass S, Bradney M, Pearce G, et al: Short stature and delayed puberty in gymnasts: influence of selection bias on leg length and the duration of training on trunk length. J Pediatr 2000;136(2):149-155

Field Notes

Shovel, Shovel, Toil and Trouble...
This winter promises to be one of the coldest and snowiest on record in many parts of the country. Shoveling often leads to back, neck, shoulder, and wrist injuries. The American Academy of Orthopaedic Surgeons has issued snow safety recommendations for inexperienced shovelers and those who have grown complacent over the years.

• Be aware that shoveling snow is an aerobic activity. Do 10 minutes of warm-up exercise, pace yourself, take frequent breaks, and drink fluids to prevent dehydration.
• Push the snow instead of lifting it. If you must lift, keep your feet apart, knees bent, and back straight. Lift with your legs. Walk to where you will dump it. Don't twist your spine by throwing snow over your shoulder or to the side.
• Watch out for ice patches and uneven surfaces. Wear slip-resistant soles. Don't let clothing obscure vision.
• Shovel early and often, before the snow gets packed down. Attack deep snow in 1- or 2-in. layers, rest, then repeat.
• Hire someone to remove snow if you have a medical condition or do not exercise regularly.

Back Belts and Workplace Injuries
Does wearing a back-support belt provide a measure of safety for workers who consistently handle heavy materials? A study in the December 6 issue of The Journal of the American Medical Association concludes that wearing a back belt does not significantly decrease the rate of reported back pain or workers compensation claims for back injuries. A history of back injury was the strongest risk factor for both outcomes.

The prospective cohort study involved 6,311 workers (who completed both baseline and follow-up interviews) at 160 supermarket-merchandise stores. Belt use was required at 89 stores, and belt use was voluntary at 71 stores.

The authors note that when compared with past studies of back belt use, their study more closely measures use because individual surveys were done rather than depending on implied use based on store belt-use policy. The study also differs from past belt-use reports because it adjusted for multiple risk factors such as history of back injury and lifting frequency.

Adding an Exercise Brick to the Food Pyramid
There's no such thing as a Mayo Clinic diet but scientists at the clinic have a new food pyramid that is designed to help overweight people lose and maintain a healthy weight. The food pyramid appears in a new book titled Mayo Clinic on Healthy Weight (Kensington Publishing Corp, New York City).

Unlike the more familiar food pyramid, physical activity—rather than food—is at the center of the Mayo pyramid to emphasize the importance of regular activity. Unlimited amounts of fruits and vegetables, unlike the carbohydrate base of other food pyramids, form the base of the Mayo Clinic pyramid. The next levels are whole-grain products (four to eight servings per day), protein-dairy (three to seven servings), heart-healthy fats (three to five serving), and sweets (75 calories per day). The strategy is to feel fuller and avoid hunger by consuming larger amounts of foods that have fewer calories.

Get Fit by Skipping
Your favorite childhood activity may be the next fitness craze if Kim Corbin of San Francisco has her way. She maintains that skipping can burn as many calories as running, is less stressful on the joints, can be done at varying intensities, and offers a joyful workout as opposed to running, which comes from our flight-or-fight reflex. Corbin has lost 25 lb since she began skipping in 1999. She also hopes to persuade thousands of parents and children to exercise together.

Corbin claims that skipping is also a tremendous mood lifter. Initial research shows that as few as 10 steps can increase positive affect, which may have useful clinical applications. Corbin notes that it takes courage to turn off your inner critic and not worry about what others will think when they see you skipping.

Corbin has a Web site that lists cities with skipping contacts, skip tips, and other inspiring information (http://www.iskip.com).