WASHINGTON (AP) — After hearing from brain trauma researchers who said playing football at a young age is unsafe even for kids who don't suffer obvious injuries, members of Congress on Tuesday asked the governing body for the sport's amateurs to detail efforts to make the game safer for children.

Democrats on the Energy and Commerce Committee sent a letter to USA Football seeking details on how it evaluates the safety of tackle football programs for kids. USA Football recently launched a pilot program called Rookie Tackle for younger kids that uses smaller teams and fields plus rules intended to reduce contact.

Researchers at Boston University found in a study published last month that playing tackle football before age 12 can more than double the risk of behavioral problems and depression later in life.

A senior author of that study, Robert Stern, told the committee at a forum last week that researchers have not yet determined at what age it may be safe, or at least safer, to start playing football. He recommended young kids avoid the sport because routine collisions can cause brain damage.

"There is not necessarily a safe time for the head to be hit and for the brain to be moved around ... over and over again. It's just not made to do that," Stern said. "To do whatever can be done to reduce the overall number of hits is critical."

The letter seeks details on what USA Football is doing to determine whether Rookie Tackle is any safer than conventional tackle football. It also asks whether USA Football believes there is an age where tackle football is inappropriate.

A previous study commissioned by USA Football about its Heads Up Football program made claims about safety that were later found to be misleading. The program was ultimately found to have no effect on the number of concussions or head injuries.

USA Football executive director Scott Hallenbeck told AP the organization is focused on developmental aspects of Rookie Tackle and is not necessarily claiming it is safer.

"I don't have any information that otherwise would say this form of football is safer than another form," Hallenbeck said. "We sort of learned that's a very, very challenging space. You need a lot of research. It takes a long time."

Melinda Whitemarsh, a spokeswoman for the organization, said it will respond to the letter.

"We welcome the members' interest in our Rookie Tackle pilot program," she said, "and look forward to providing them with the information requested."

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