FRIDAY, June 1 (HealthDay News) -- Spending too much time in front of computers and other electronic screens may cause American children's heart and lung fitness levels, or "cardiorespiratory" fitness, to decline, a new study suggests.

Cardiorespiratory fitness involves the body's ability to transport oxygen to muscles during exercise.

The study included more than 2,000 children who were followed from ages 11 to 13. Each child reported their screen time and completed shuttle run laps to assess their fitness level.

Children who reported more screen time completed fewer shuttle run laps, the investigators found. This association was strongest in children with mid-to-high cardiorespiratory fitness levels, and was independent of physical activity levels.

The study was published in the June issue of the journal Medicine & Science in Sports & Exercise.

"The results are interesting and add to the evidence that spending too much time sitting is hazardous to children's health," study lead author Jonathan Mitchell, who conducted the research while at the Arnold School of Public Health, University of South Carolina, said in a news release from the American College of Sports Medicine.

"If children limit the amount of time spent sitting in front of a screen, then this could help to combat declining levels of cardiorespiratory fitness in youth," he added.

While the study uncovered an association between more screen time and less cardiorespiratory fitness, it did not prove a cause-and-effect relationship.

-- Robert Preidt

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Too Much Screen Time May Harm Kids' Fitness