Children will meet activity goals to earn rewards, but the extra effort doesn't necessarily affect their weight and health, according to a new study.
The findings reinforce earlier research showing that incentives work to get kids more physically active, but the goal might need to be more challenging to show any health benefits.
"If I had to do it again I would do it at a higher level. It was too easy," said Eric Finkelstein at the Duke-National University of Singapore, who led the new study.
Inactivity among kids is a pressing concern in the U.S. and abroad.
"Kids are known to be inactive, getting five hours a day of screen time," said Gary Goldfield, a scientist with the Healthy Active Living and Obesity research group at the Children's Hospital of Eastern Ontario, who was not involved in the study.
Finkelstein and his colleagues designed a program meant to encourage more physical activity among elementary school-age kids.
All of the children in the study wore a pedometer for an average of nine months to measure how many steps they took each day.
One group of 138 kids was told to aim for a minimum of 8,000 steps per day (for an adult that's about four miles).
Each month, the kids who met this goal for at least half of the days received a Toys-R-Us gift card worth about $24.
In addition, this group was encouraged to attend outdoor events with enticements to win theme park or zoo tickets.
The researchers compared this group of children to another group of 113 kids who wore a pedometer, but were not given any incentives or offers to participate in outdoor activities.
At the beginning and the end of the study the researchers collected the kids' height and weight, heart rate and other physical and mental health measures.
They found that the kids who were offered incentives were more active, logging an average of 8,660 steps per day, compared to 7,767 steps per day in the other group.
"The results are not whopping," Goldfield said.
The modest difference in activity between the groups might explain why the researchers didn't see any differences in body mass index (BMI) - a measure of weight relative to height - or in their overall health at the end of the study.
"I don't think that's enough to see differences in BMI and other health indicators," Goldfield told Reuters Health.
Despite the lack of health benefits, the findings demonstrate that incentives can work to get kids more active, he added.
"If you look at the percentage of people who met the 8,000 steps per day goal, then you get larger effects," Goldfield said.
Just two percent of the kids in the no-rewards group reached 8,000 steps each day, compared to 24 percent in the rewards group, the researchers report in The Journal of Pediatrics.
"Incentives are important for the adoption of behaviors," and starting out with easily-attainable goals is not a bad idea, Goldfield said.
Finkelstein said his group is planning to do a study with a more challenging goal.
Finkelstein attributes the increased activity to the rewards the children were given, and not to the outdoor activities they were offered.
That's because far fewer families attended the outdoor activities by the end of the study, but many kids continued to meet their steps-per-day goals.
He also said that it's possible even modestly increasing the levels of activity could have longer term benefits - such as a slowing of weight gain - that would not be picked up in a study that lasted nine months.
"There are benefits to getting them active while they're young, they just won't accrue until they're older," he told Reuters Health.
Although there is a cost to implementing such a program, Finkelstein and his colleagues argue that it's worthwhile if it could curb obesity rates.
"To me, $25 to keep kids active is a small price to pay. If you can do it and it works, I think this is the sort of thing that should be fostered," he said.