Black Girls Are Less Fit Than Whites, Researchers Say : Health: Participants in study of aerobic abilities were average teenagers. Results surprise experts.

WASHINGTON —  Researchers who found that young black teenage girls are less aerobically fit than their white counterparts now wonder what to make of their discovery.

“It surprises us too,” said William W. Wong, a professor in the pediatrics department at Baylor College of Medicine in Houston. “If you look at Olympic competition, most of the very good runners are African American.”

The teenagers studied by Wong and his colleagues were not elite athletes; he described them as average kids. “The basic requirement is healthy, not overweight, not underweight,” Wong said. While they were not in poor shape, they were not athletes either, he said.

The study was intended to get baseline data on the aerobic abilities of blacks and females, because scientists have tended to do most studies on whites and males, Wong said. The researchers looked at 40 blacks and 53 whites, ranging in age from 11 to 16 but averaging 13 1/2 years.

The researchers checked to see whether one group was fatter than the other--extra weight can reduce fitness. They also checked social status; poorer people tend to have less access to workout facilities or even safe neighborhoods to run in. And they checked the girls’ physical maturity.

The two groups had about the same percent body fat, and most were daughters of medical center employees, whose socioeconomic backgrounds were similar, the study said. But the black girls were larger and more physically mature, it said.

The researchers looked at aerobic capacity, the body’s efficiency in using oxygen, by measuring oxygen consumption and carbon dioxide production while the girls ran on a treadmill until they were no longer able to continue.

The black girls reached exhaustion in 8.5 minutes, compared with 9.4 minutes for the white girls, the study found. Similarly, the black girls were less efficient in using oxygen, using 17% less than the white girls, said the study in the American College of Sports Medicine’s journal, Medicine and Science in Sports and Exercise.

Blood tests showed that the black girls had 6% less hemoglobin--the oxygen-carrying red blood cells--than did the white girls, the researchers found. But this difference might be another sign of the overall aerobic gap, not its cause, Wong said. Wong and his colleagues are still looking for causes.

One possibility is that the black girls were ordinarily less active than the whites, the study said. A 1990 federal survey found that black females in grades 9-12 were least likely to be vigorously active at least three times a week, it said. The researchers are developing a questionnaire that focuses on teenage activities, Wong said.

Another possibility is that the black girls had less muscle and more bone than did the white girls, the study said. The additional weight of bone, coupled with less muscle, could help to explain the differences in aerobic potential, it said.

The findings fit other studies on aerobic differences in blacks and whites, said Jerome Brandon, an associate professor in the Department of Kinesiology and Health at Georgia State University in Atlanta.

Earlier studies have found that black women were less aerobically fit than whites, Brandon said. The Wong study indicates that the difference may develop earlier than adulthood, he said.

“To me, the question is not whether there is a division, but what is causing it,” Brandon said. “I wonder if it’s lifestyle or some other characteristic. I choose to believe it’s probably lifestyle, but I can’t verify that.”