Too much TV may do more than interfere with a child's grades. It also might affect his or her athletic development - a potential problem for those parents who dream of raising the next Michael Phelps or Serena Williams.
A study published in the International Journal of Behavioral Nutrition and Physical Activity is believed to be the first to document the relationship between how much TV screen time a child logs and later explosive leg strength, a key indicator of athletic prowess.
The other key finding, while significant, is perhaps less surprising: Kids who watch more TV early in life were likely to have wider waist measurements down the road, an indication that lack of activity put young children on a path toward obesity.
"Watching more television in early childhood forecasted lesser performance on a test of explosive muscular strength in later childhood. ... This suggests that for some children, excessive television exposure was associated with the experience of a substantial level of impairment," the study found.
Lead researcher Caroline Fitzpatrick, a post-doctoral researcher at New York University, joined researchers at the University of Montreal to study 1,314 children in Quebec. Parents participating in the study were asked how much time their children spent watching television at ages 29 months and 53 months.
As second-graders, the children were tested using a standing long jump as an indicator of explosive leg strength, speed and power. As fourth-graders, their waists were measured with a tape measure.
The study is the latest to suggest that parents who want to raise healthy kids need to slash their screen time.
"Children who watch more television are more likely to develop poor dietary habits, sleep disturbances, and become obese," the study said. "Because it represents a sedentary activity which takes time away from other more physically demanding pursuits, the amount of time children spend watching television in early childhood raises concerns over potential consequences for later physical fitness during the school years."
But how much TV is too much? The study doesn't say, specifically. But it does say that each hour of TV per week at 29 months corresponds to a diminished performance in the standing long jump. Further, the increase of an hour per week between 29 months and 53 months was linked to an even worse performance in the standing long jump — and measurable increase in waist size.
But the study concluded: "Early interventions aimed at modifying toddler viewing habits may contribute to subsequent physical health and athletic performance."