Athlete’s Cap Sends Out Alerts About Head Injuries

Signals let coaches know when an injury occurs on the field

22 November 2013

Research shows that repeated hard knocks to the head during impact sports can cause long-term brain injury. But it can be hard for coaches watching from the sidelines to tell how hard a blow really was.

That’s why IEEE Member Roozbeh Ghaffari helped develop a skullcap to be worn alone or underneath a helmet that detects how hard a player’s skull is hit. Depending on the severity of the impact, different colored LEDs light up on the back of the cap for all to see.

Ghaffari, a biomedical engineer by training, is a cofounder of the five-year-old MC10 (Materials Company 10), in Cambridge, Mass., which designs wearable health-monitoring devices, including sensors on the skin for physiological monitoring. MC10 worked with professional athletes to help develop the cap, which it calls CheckLight. It’s now sold by Reebok—the athletic apparel maker—for US $150.

CheckLight was launched in July, when sports-related brain injuries coincidentally were making headlines. In the United States, retired National Football League players reached a $765 million settlement with the league over head injuries. Some had been diagnosed with conditions such as Lou Gehrig’s disease, a progressive neurodegenerative disease that affects nerve cells in the brain and spine, leading to an early death. They are to receive up to $5 million each, as did the families of athletes who had committed suicide and who were found on autopsy to have had early onset Alzheimer’s and other brain disorders.

Despite the recent awareness, “there’s still a stigma around monitoring head impact in the sporting world because an injury means the player has to come off the field,” Ghaffari says. “This product is about changing the mentality of players, especially at a young age, by introducing an easy way to screen for a potential brain injury early on.” 


An estimated 2 million to 4 million sports-related brain injuries occur around the world each year, according to the Brain Trauma Foundation, in New York City, which conducts clinical research on traumatic brain injury, more popularly known as a concussion. Children alone make more than 500 000 hospital visits in the United States each year for TBI, largely because of sports play, according to the U.S. Centers for Disease Control and Prevention.

As part of its research, MC10 created a sports advisory board that includes Isaiah J. Kacyvenski, former NFL linebacker and MC10’s head of sports, as the board chair and Indianapolis Colts quarterback Andrew Luck, who was the number one draft pick this season. The product has also garnered support and media attention from other athletes, including Chris Nowinski, a former professional wrestler for World Wrestling Entertainment. The cap can be used for all high-impact sports, including boxing, hockey, lacrosse, wrestling, and even snowboarding because of falls, as well as football.

“By the time I got to the NFL, I became a master at masking pain,” says Kacyvenski. “I continued saying I can tough through it, but not so with a head injury. The cap makes monitoring head injuries objective and measurable, and takes away the decision from players to stick it out in a game no matter what the consequence.” He is now lobbying the NFL to have players wear the CheckLight during games.


MC10’s earlier research in neuroscience and wearable technology led it to conclude that a cap worn close to the head would be better for monitoring hard hits than a helmet embedded with sensors. “The helmet absorbs a lot of the impact,” Ghaffari says. “You don’t actually get a sense of what the skull is experiencing unless the sensors are on the surface of the head.”

But for athletes to wear the cap, MC10 had to make it comfortable as well as practical. Collaborating with Reebok, MC10 modeled its cap after the beanie, or skullcap, made with elastic that many athletes wear alone or under their helmets to keep hair and sweat from their faces.

The researchers then developed an electronic monitor packed with sensors that fits inside the cap. The device incorporates a semiconductor tri-axial accelerometer to measure acceleration of the skull, which occurs when the head is hit hard. There is also a semiconductor gyroscope to measure rotational acceleration when an athlete’s head snaps back or hits the ground after a fall. These sensors are integrated with a microprocessor that calculates the impact using an algorithm similar to the head injury criterion used to assess the intensity of impact in sports.


The cap has three LEDs that appear below the helmet line on the back of the neck. When the player’s head is hit, the LEDs light up in perpetuity until reset. A green light, which is always on, means the cap is on and working, yellow signifies that the player experienced a moderate impact, while a red light indicates that the head has received a severe jolt. Such a hit may require the athlete to leave the game. The user can also remove the cap to check if an impact was serious.  

The monitor can be removed, charged, and reinserted from a flap opening underneath the cap. A single charge can last six to eight hours, enough for about two or three games.

The researchers fitted the CheckLight caps on the heads of test dummies. Dropping them headfirst from different heights simulated impacts athletes would experience during a game. After the accelerometer outputs were calibrated to distinguish minor from serious force, the team recruited athletes of all ages across contact sports to test the cap in their practice games.

“One thing that we weren’t expecting is that players, particularly kids, would modify their tackling techniques on purpose—moving their head out of the way in moments of impact—to avoid getting that red or yellow light,” Ghaffari says. “That alone will make the game safer.”


The CheckLight also can help athletes monitor how often their heads are jolted. When charging the monitor, the LEDs will blink green for every 100 minor impacts received since the cap was first used, yellow for every moderate one, and red for every severe hit.

“The small hits add up over time, and tracking them could be the difference between longevity in a sport versus having to retire early because of injury,” Ghaffari says.

While CheckLight is not a diagnostic tool, he says, “it is an extra set of eyes on the field.”

To watch the cap in action, visit our multimedia page.

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