Young girls may not be getting the exercise they need to remain healthy because a time-honored standard for measuring their physical activity levels may not be as accurate as originally thought, research at Michigan State University has shown.
Until now, exercise that raises a girl's heart rate from between 140 to 160 beats a minute was considered sufficient. However, research by James Pivarnik, professor of kinesiology and osteopathic surgical specialties, and Karin Allor, a graduate student in kinesiology, found that even at 160 most girls were not using as much energy as previously thought.
The research is published in the August issue of the journal Pediatric Exercise Science.
"If you use these heart rate levels, the intensity level is not as high as it should be," Pivarnik said. "They are not getting the workout they should be getting."
To reach this conclusion, Allor and Pivarnik measured the energy output levels of 49 middle-school girls while the girls ran on a treadmill. The girls would start off slowly and eventually speed up. At each level, heart rates and energy output levels were measured.
It was determined that girls who reached a heart rate of 140 were using only 46 percent of their maximum energy output. Girls whose heart rate was 160 were using only about 63 percent of their maximum energy output.
"I would say the heart rate numbers we currently use are off by about 20 beats per minute," Pivarnik said. "The 160 heart beats a minute should probably be more toward the lower end. The traditional cut points for exercise levels need to be adjusted upward."
While it is important that kids be active at any intensity level, it also is important for researchers to develop standards based on scientific research.
"If we're going to come up with standards, if we're going to try to intervene and tell kids they need to be this active, then we've got to give them the right numbers," he said.
The girls who took part in the project were "typical" sixth-grade students, Pivarnik said, running the gamut from athletes to those not in the best physical condition.
Middle school is a particularly crucial time in an adolescent girl's life, especially when it comes to exercise and fitness.
"It's critical because this is the age that many girls tend to lose interest in staying active," Pivarnik said. "They start asking themselves, 'Is it cool to be in sports or to exercise?'"
An MSU faculty member since 1994, Pivarnik, also is director of the Human Energy Research Laboratory.
The lab provides testing and evaluation for MSU and the surrounding community. It works with MSU Sports Medicine to perform cardiopulmonary and body composition analyses for various varsity athletic teams. It also receives referrals from MSU Sports Medicine, other clinics, and health clubs.
Contact: James Pivarnik, Kinesiology, (517) 353-3520 orTom Oswald, University Relations, (517) 355-2281
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