For teens to be fit, they shouldn’t sit

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It’s no secret that for young people, the lure of the television and the computer can take time away from playing and other forms of physical activity.

A new study suggests that for some, more time spent in front of a screen means poorer aerobic fitness, and that two hours may be the cutoff time before it adversely affects kids’ cardiovascular endurance levels.

Researchers looked at recreational time spent in front of a screen and aerobic capacity of 2,750 adolescent students in grades six, eight and 10 in New South Wales, Australia. The teens were asked to log how much time they spent in sedentary activities such as watching TV or playing on the computer, and were also given a cardiovascular endurance test in which they had to run at a certain pace; their scores were then converted into laps. The participants were categorized by grade, gender, and whether they were spending less or more than two hours a day in sedentary activities.

Among boys in grades six and 10 and and girls in grade six, there was little statistical difference in the number of laps completed, regardless of how much screen time they racked up. However, eighth-grade boys who spent more than two hours a day in front of the computer or TV ran 16% fewer laps than those who registered less than two hours. And among girls in grades eight and 10, that gap widened even more — those logging more than two hours a day of screen time finished 34% (eighth grade) and 26% (10th grade) fewer laps than their less-sedentary counterparts.

The study authors believe that a growth spurt that older teen boys experience might account for their performance; they write, ‘(They) may have developed sufficient muscle mass to enable them to maintain fitness in parallel with large amounts of sedentary behaviors: they can ‘sit but be fit.’ ‘

The authors say more research is needed to understand how being sedentary affects youth health, but they do believe there are enough data to suggest that young people should spend less than two hours a day being still while sitting in front of a screen. The study was published in the February issue of the American Journal of Preventive Medicine.

-Jeannine Stein

Photo credit: Lori Shepler / L.A. Times