Prepubescent boys involved in a sport or organized physical activity appear to spontaneously boost their overall physical activity without getting more rest, researchers report.

However, this was not seen among boys who had reached puberty, Dr. Udo Meinhardt, at the Center for Pediatric Endocrinology Zurich, Switzerland, and colleagues report in the Journal of Pediatrics.

"There may be a window of opportunity to induce or trigger more spontaneous physical activity in children," Meinhardt told Reuters Health. If confirmed, this "window" might be tapped to enhance obesity prevention programs.

Over a 4-day period, the investigators measured daily energy expenditures during training and spontaneous physical activity among 66 ice-hockey players, 5 to 15 years old. They also measured sleep duration of the 46 prepubescent players who had an average chronologic and biologic age of about 9 years, and the 20 pubescent players who had an average chronologic and biologic age of nearly 14 years.

"We were able to show that prepubertal healthy boys had higher spontaneous daily physical activity the more intense they were training," said Meinhardt, and they did not compensate for their high-intensity physical activity with more rest.

The investigators did not find a similar association among the athletes who had reached puberty, leading Meinhardt and colleagues to surmise that pubertal boys may be taking on an adult pattern in which more intense training leads to more rest.

The investigators are completing similar research to see if similar associations exist in general school children. They also suggest further studies to determine if associations between regulated and spontaneous physical activity and if the need to rest is an age-associated biological response or if it is a result of other external factors.

Nonetheless, these findings provide additional evidence of a child-specific control of physical activity that may converge to a more adult-type pattern after puberty.