Physical inactivity is a major risk factor for diseases such as obesity, diabetes and hypertension. LSU AgCenter nutritionist Dr. Heli Roy says declining levels of physical activity may help explain why childhood metabolic diseases are becoming more common.
Current studies confirm that children are becoming less physically active. Some investigators have proposed that the behavior of physical activity is primarily determined by genetic factors.
But, Dr. Eric Ravussin from the Pennington Biomedical Research Center, together with other researchers from Alabama and Arizona, studied 100 6- to 7-year-old twin pairs to determine whether it is the genes or the environment that determines a child’s physical activity level.
Roy says they assessed physical activity by various laboratory methods to determine accurately the daily energy expenditure from physical activity versus sleep and rest.
Most twin pairs were European-American, but Hispanic, American-Indian and African-American twins also were included. A physical activity questionnaire, completed by the parent, was used to assess average hours per week over the past year in which the child was typically engaged in sports and recreational activities requiring a greater expenditure of energy than that normally needed for daily grooming, bathing and eating.
Additional questions assessed the number of hours children engaged in sedentary activities such as napping, sleeping, watching television and playing computer and video games. The children had their heights and weights and body composition assessed as well.
The results show that shared environmental factors accounted for majority of energy expended by children (almost 60 percent), whereas genetic factors explained only about one-fifth of the energy expended in a day (19 percent of total energy expenditure).
The children participated in about six different types of activities over a year’s time, and the average time spent in activities per week was 11 hours. This was true for male and female sets of twins at different ages.
Roy says this study shows that the shared environment is an important factor in physical activity, determining almost 70 percent of the activity level. Genes play a much smaller role in determining physical activity level – only about one-fifth of the activity level in children.
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