Genetic and Other Factors
Reviewed
The American College of Sports
Medicine recently published a study in its official monthly journal,
Medicine & Science in Sports & Exercise that assesses the
influence of competitive sports of prepubertal growth. Much of the recent
attention to the relative youth of participants in competitive sports
can be traced to international media attention to the manner of recruitment
used to find Olympic level athletes and train them early. The purpose
of this study was to assess not only pubertal status, but genetic factors,
birth weight, early childhood growth, the sport involved, hours spent
training and age as well.
The team of researchers,
led by Rasmus Damsgaard, University of Copenhagen, Denmark, realized
that previous studies had shown that growth is restricted and puberty
delayed in some sports and not in others. For this reason, it had been
suggested in some arenas that female gymnasts should decrease training
during puberty. "We know that hard training sometimes seems to have
an adverse effect on growth and puberty," said Damsgaard. "But constitutional
and nutritional factors play a role, and we designed a study that would
provide some indication of predisposition in assessing the effects of
sports participation on growth." The Danish Sports Association provided
contacts with sports clubs that sponsored well-regarded nationally or
regionally competitive training programs for children in swimming, tennis,
team handball and gymnastics.
Ten of the clubs selected
boys and girls between the ages of nine and 13 years, and 184 (96 girls,
88 boys) agreed to participate. They were asked to provide birth date,
birth weight, standing height and weight at age two to four, the height
of their parents and the number of training hours per week. To reduce
variation in reporting measurement, one examiner, using the Tanner scale,
assessed the girls' stage of puberty; likewise a single pediatrician
examined the boys, using the Prader measurement. The researchers then
used a linear regression model to assess the significance of age, target
height, birth weight, height and body mass index (BMI) at age two to
four, the sport, training hours and stage of puberty on actual height
and current BMI.
The analysis showed that target
height, height at two to four years and the current stage of puberty
were significant to actual height. In boys, BMI at two to four years
and stage of puberty were significant to actual BMI, and in girls only
BMI at two to four years was significant to actual BMI. The only difference
in target height relative to the specific sport occurred in tennis players,
where the target height for girls was significantly higher than in the
other three sports.
The researchers concluded
that in their relatively large sample, type of sport and number of training
hours had no impact on size attained, whereas genetic factors, size
attained before starting training and stages of puberty were important
factors.
They did find significant
differences in height among the nine-to-13-year old children, but those
differences also had existed at age two to four.
The female gymnasts were smaller
than the female swimmers at both stages. Growth in infancy, said Damsgaard,
depends on nutrition and prenatal factors, but from age two on, it is
constant except for adverse events. This suggests that training for
and participating in sport have no negative influence on growth. Similarly,
the number of hours spent training per week has little negative influence,
suggested by the fact that both boys and girls trained in gymnastics
significantly more than in the other sports. The results did not demonstrate
any decrease in height or change in BMI among the four sports, although
it must be noted that most of the children in the test trained less
than the 15-18 hour per week recommendation.
Prepubertal growth is not
adversely affected by sport at a competitive level, noted the researchers.
They indicated that their statistics point toward constitutional factors
greatly influencing a child's choice of sport, explaining in part the
selection of gymnastics by smaller girls and boys, and tennis for taller
girls. Children are influenced by parental choice as well, which also
bears out the theory of constitutional selection.
| The American College
of Sports Medicine is the largest sports medicine and exercise
science organization in the world. More than 17,000 members throughout
the U.S. and the world are dedicated to promoting and integrating
scientific research, education, and practical applications of
sports medicine and exercise science to maintain and enhance physical
performance, fitness, health and quality of life. For a complete
copy of the research paper (Medicine & Science in Sports
& Exercise, Vol. 32, No. 10, page 1698) or to speak with
a leading sports medicine expert on the topic, contact the Public
Information Department at 317-637-9200.
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