Most parents have heard the news: The current crop of American children is overweight and less fit than previous generations. Health conditions that used to be seen only in adults — Type II diabetes, abnormal lipids, and elevated blood pressure — now more often appear among children and teens.

Research shows that fitness is declining because children exercise less, partly because they spend too much time in front of a computer or phone screen. There are also fewer outdoor spaces available for play; and an increased emphasis on academic achievement has meant that school systems have reduced recess and gym time in an effort to increase teaching time.

More exposure to active peers may be one way to get inactive children and adolescents moving.

Luckily, there is a way to increase children's activity levels: Friends.

Canadian researchers found that friends often have a large and positive influence on children's activity levels. If their friends are active, it's more likely a child will also be active. And when children and teens have friends who are less active, they tend to be less active.

The researchers did not find a connection between friends and sedentary behaviors such as watching TV or playing video games.

Their review of published studies on kids' activity levels suggests that increased contact with active peers may be one way to get inactive children and adolescents to become more active.

When peer groups increased their level of physical activity over time, individuals followed. Unsurprisingly, boys were more influenced by their peer group’s level of activity than girls and were more likely to join teams when their friends were on teams.

There are several possible explanations for their findings, according to the researchers. Children and teens with similar interests do tend to seek each other’s company, so more physically active kids form friendships with like-minded peers. This is certainly true of the friendships forged through organized sports.

But it is also true that peer pressure within a group, and the desire to be part of a group, can inspire a child or teen to take on a behavior that they might not naturally adopt. When a group of peers models a behavior, a child or teen is far more likely to become interested in the activity and feel more comfortable trying it.

Neighborhoods or schools that have an active community of bicyclists, for example, are likely to inspire other children to give cycling a try. Seeing classmates or friends who are already participating in an activity —whether it's Tae Kwon Do or yoga or handball — provides support for the novice who is uncertain about undertaking a new behavior alone.

The study confirms that there is a relationship between friends’ physical activity level and an individual’s activity level and suggests that this finding can be used to promote better exercise habits.

The researchers, all at the University of Calgary, conclude that, “Harnessing the influence of friendship to increase physical activity levels and decrease sedentary leisure-time activity would have a beneficial impact on reducing the current prevalence of overweight an obese youth through an increase in energy expenditure,”

The study is open access and published in The International Journal of Behavioral Nutrition and Physical Activity.