The study of 1,314 children from the Quebec Longitudinal Study of Child Development Parents were asked, “How much time per day does your child spend watching TV?” at 29 months and then again at 53 months. A two-part follow-up test of muscular fitness was conducted on these children when they reached the second grade. First, the children were asked to do a standing long jump test. Second, the children’s waist circumference was measured.

By the numbers: One hour of TV at 29 months led to a 3.61 millimeter decrease in standing long jump results in the second grade. Every hour of TV from 29 months to 53 months led to a 5 percent increase of being in the bottom percentile of the standing long jump test.

One hour of TV from 29 months to 53 months led to a .42 millimeter increase in waste measurement and 18-plus hours per week of TV led to a 7.6 millimeter increase in waste measurement in the second grade.