NEW YORK, (Reuters Health) -- Contrary to popular opinion, girls
may be as aerobically fit as boys, according to a report published in the
British Journal of Sports Medicine.
The belief that girls' aerobic fitness is not on a par with boys' fitness
may have come from inappropriate methods used to measure fitness without
properly accounting for changes in body size during growth, writes study author
Dr. Joanne Welsman, deputy director of the Children's Health and Exercise
Research Centre at the University of Exeter, UK.
"Girls' fitness increases from prepuberty into adolescence and then
stabilizes into young adulthood," Professor Neil Armstrong, director of the
Children's Health and Exercise Research Centre, told Reuters Health.
The "gold standard criterion" for measuring aerobic fitness is the peak
amount of oxygen used during progressive exercise until the point of exhaustion.
This oxygen level is usually associated with body size values, and expressed as
ratios to body mass. These ratios typically show a decline in the level of
oxygen used by girls between the ages of 8 and 16. This declining ratio seems to
contradict the potential for improved oxygen use and delivery that arises during
adolescence, notes Welsman in her report. She suggests the supposed decline in
fitness may be solely based in statistics as opposed to physiology.
When the correct measures are used to assess aerobic fitness --
controlling for body mass -- "girls' fitness can be seen to increase
significantly," Welsman writes. The increase, however, is still below the
aerobic fitness level of boys.
"Girls are less active than boys from as young as 5 years of age,"
Armstrong told Reuters Health. For example, 85% of 5-year-old girls are active
for 30 minutes a day, but only 20% of 14-year-old girls have similar levels of
activity. "Sustained physical activity (in girls) is rare," Welsman adds, with
45% of teenage girls not even managing a brisk 10-minute walk during a monitored
3-day period. However, Welsman's research shows that these low activity levels
"do not appear to influence" aerobic fitness.
"These findings are very positive," Welsman concludes, "but present no
grounds for complacency. The inactive lifestyle of the average girl remains a
serious concern, particularly given the importance of activity during
adolescence for optimizing skeletal health."
