Washington, Mar 10 : A new study has explained why children with attention deficit hyperactivity disorder move around a lot - it helps them stay alert to complete challenging tasks.

Researchers from University of Central Florida have discovered that

children with ADHD need to move more to maintain the required level of alertness while performing tasks that challenge their working memory.

"We''ve known for years that children with ADHD are more active than their peers. What we haven''t known is why," said psychology Professor Mark D. Rapport.

"They use movement to keep themselves alert.

"They have a hard time sitting still unless they''re in a highly stimulating environment where they don''t need to use much working memory," he added.

During the study involving 8- to 12-year-old boys, those with and without ADHD sat relatively still while watching Star Wars and painting on a computer program.

While all of the children became more active when required to remember and manipulate computer-generated letters, numbers and shapes for a short time, kids with ADHD became significantly more active - moving their hands and feet and swivelling in their chairs.

The researchers suggest that parents and educators can use a variety of available methods and strategies to minimize working memory failures.

Providing written instructions, simplifying multi-step directions, and using poster checklists can help children with ADHD learn without overwhelming their working memories.

"When they are doing homework, let them fidget, stand up or chew gum," said Rapport

"Unless their behaviour is destructive, severely limiting their activity could be counterproductive," he added.

The study appears in the Journal of Abnormal Child Psychology. (ANI)