The days of coaches telling kids to “walk it off” or “skate through it” after getting their “bell rung” from a blow to the head appear to be numbered in Minnesota.

Instead, the mantra is becoming, “When in doubt, sit them out.”

And it might become law.

Bipartisan support has emerged at the Legislature for a proposal that would require young athletes, including in school-sponsored sports and most community and independent leagues, to stop playing if they have a concussion or are suspected of having one. The athletes would have to remain benched and potentially not attend practice, until all symptoms are gone and an expert has cleared them to play again.

The strong stance, which has been adopted by 13 states and is under consideration in 28 others, is the result of significant advances in the last decade in understanding brain injuries and the prevalence of them among athletes.

From pee-wee hockey to the National Football League, virtually every level of high-contact sports is rethinking rules, equipment and how the game is taught with an eye toward protecting the most vital body part, yet the one often overlooked because it’s out of sight: the brain.

A concussion — which is nothing short of a traumatic brain injury — doesn’t show up on an X-ray or MRI like a broken bone or torn ligament, but its effects can be far more serious, several doctors and sports medicine experts testified at a public hearing Wednesday.

“You don’t die from a torn ACL, but you can die from this,” said Dr. Michael Bergeron, director of the National Institute for Athletic Health and Performance and a pediatrics professor at the University of South Dakota’s Sanford School of Medicine.

Bergeron told members of the House Health and Human Services Reform Committee that a concussion, in which back-and-forth or twisting forces damage the brain on a cellular level, leave the organ in an “energy crisis.”

Dr. mark Carlson, who practices sports and occupational medicine at a Bemidji, Minn., clinic, said the only treatment is rest — both physical and mental.

“I tell my patients you need to sleep, or if you can’t sleep, pretend to sleep,” Carlson testified, noting that in many cases, a youth with a concussion should remain home from school, confined to bed. Even playing a video game can be too much stimulation, he said.

Failure to do that can lead to long-term problems, including headaches, an inability to concentrate and nausea.

The brain that’s healing from a concussion is more vulnerable to long-term or permanent damage if the player receives a second concussion.

That’s what happened to Kayla Mayer, a freshman at new Prague (Minn.) High School whose hockey career was cut short after suffering a concussion in 2009. her career, which began at age 3 playing on a pond near her house, might have lasted longer had her participation been cut short after her first concussion.

Kayla and her doctors believe she suffered the concussion while playing and then, because neither she nor her coaches were aware of the symptoms, continued practicing and playing for another 10 days. then during a practice drill, she was upended and smacked the back and top of her helmeted head on the ice. The next day she was dealing with a horrible headache and couldn’t figure out why. she asked her friends.

“They said, ‘Don’t you remember falling and hitting your head?’ ” she told lawmakers Wednesday. “As soon as they said that, then I remembered.”

She still tried to return to play, but her head was so sensitive she couldn’t put on her helmet. she was diagnosed with a mild traumatic brain injury, but don’t let the “mild” fool you. She’s given up hockey for good, and she said she’s given up a lot more than just the game.

“I have a headache every second of every minute of every hour of every day,” she said. “Sitting here testifying to you, I have a headache.”

She’s especially sensitive to sounds — even a car blinker’s click can cause trouble — and a compromised attention span has led her to spend no more than three hours in class a day. because of the noise in the school cafeteria, she said, she eats lunch in a school office, usually with a few friends.

“But sometimes they forget, and I eat alone,” she said.

Kayla’s travails — and the lack of awareness she said she and her coaches had about concussions — prompted her to become the poster child and lead spokesperson for what’s become known as “the concussion bill.”

In addition to requiring that athletes suspected of suffering concussions be pulled out of play until cleared by a qualified person, such as a trainer or physician, the bill would require coaches and referees to review concussion-awareness materials and take a free online training course offered by the U.S. Centers for Disease Control and Prevention.

“This bill does not prevent sports concussions,” Bergeron said. “But it puts the right processes into place.”

He said the awareness of how concussions happen and how serious they are will probably prompt many coaches to reconsider drills and techniques that put their players at risk.

Perhaps the most obvious example is football tacklers who lead with their helmet — a technique that was considered unsound decades ago but has become more common as helmets have improved and weight training has allowed boys to strengthen their neck muscles.

Rep. Rod Hamilton, R-Mountain Lake, the bill’s chief sponsor, said he’s planning on modifying several aspects of the proposal to clarify that coaches, referees and school and sports officials can’t be held liable if they fail to follow the law.

“This is all about protecting our youth athletes by raising awareness,” Hamilton said.

The bill passed on a unanimous voice vote and is headed to the Committee on Government Operations and Elections. A companion bill has been introduced in the Senate.