In a recent study, children were observed as they played with weighted and unweighted cardboard blocks during sessions that averaged 10 minutes. By monitoring a metabolic measuring device the kids wore, the investigators learned that they burned more calories and had higher respiration and heart rates when hauling around the heavier blocks.

Professor John Ozmun and graduate student Lee Robbins of Indiana State University conducted the research with children 7 and 8 years old.

"This study provides one intervention to the current trend of declining fitness in America's youth," the study authors wrote.

Worrying Trends

There has been increasing alarm over obesity rates among American children and adolescents. Studies indicate they have tripled in the last four decades, and that problems associated with overweight and obesity, such as diabetes, are on the rise among the young.

More than one-third of US children are overweight, while approximately 17 percent are obese, according to government statistics. As children grow older, they exercise less, studies have indicated, which compounds the problem.

Encouraging increased physical activity is one way to help children achieve or maintain a healthy body composition. Studies have shown that exercise can strengthen kids' cardiovascular and skeletal systems, and positively impact heart rate, blood pressure and cholesterol levels.

If children can be subtlely influenced to engage in more beneficial physical activity by the simple introduction of heavier toys into their play routines, the researchers suggest, the benefits could be significant.

Caution Advised

On the other hand, some experts are cautioning that heavy toys could be harmful to children -- or playmates who might be on the receiving end of a flying block. One solution might be to place the weights in large stuffed toys. For example, Dr. Ozmun is developing a heavy teddy bear for physiotherapists to use with kids.

Ozmun does not view the use of heavier toys as a solution for childhood obesity, but rather as a small contribution toward reducing it. His goal is to alter attitudes by encouraging acceptance of more intense, physically active play.

The toys might also be useful for children with cerebral palsy, Down's syndrome or other conditions that compromise their strength, Ozmun suggested.

The researchers are not recommending that parents add weights to their children's toys, in light of as yet unresolved safety concerns.