This technical information has been contributed by
Reebok's Advanced Concepts Group

Did I Just Hit My Head? How Hard Did I Hit My Head?

Mark Shortt
Editorial Director
Design-2-Part Magazine

By embedding MC10's conformal electronics into the skullcap in a way that's not distracting to the athlete, CheckLight can provide information on the severity of head impacts that hadn't been available previously
Photo courtesy of Reebok

Wearable, high-performance electronics offer a new tool for real-time assessment of head injuries

Paul Litchfield, vice president of Reebok's Advanced Concepts Group, is on a roll as he leans into the conversation at a small, circular table in Booth 26718 of the Las Vegas Convention Center's South Hall. It's nearing 11:30 on a Thursday morning in early January, the 2014 International CES is in full swing, and Advanced Concepts' booth is teeming with visitors eager to learn more about Reebok's CheckLightTM impact indicator, winner of the 2014 International CES "Best of Innovations" Design and Engineering Award in the Health and Fitness category. Suddenly, Litchfield stops in mid-sentence. His colleague, CheckLight Program Director Paul Davis, is telling him that they need to catch a ride to The Venetian—where the CheckLight's been on display since Tuesday—in a few minutes.

"This is pretty interesting for us," Litchfield says afterward, referring to Reebok's beehive of a booth in this, their debut as an exhibitor at CES. "We're the Advanced Concepts Group; we're not booth people, and so this is a whole new kind of endeavor for us." 

People are eager to talk with Litchfield because Reebok, the iconic sports and fitness brand, and MC10 Inc., a bold, venture capital-backed startup seeking to change the way we think about electronics, have brought to market a product that could help spur the development of an entirely new class of wearable electronics. The two companies began collaborating four years ago with the intention of combining Reebok's design capability with MC10's leading edge conformal electronics platform, a trove of intellectual property that makes high-performance electronics more wearable by reshaping what have traditionally been rigid, boxy structures into extremely thin systems that can stretch, bend, and flex with the natural contours and movements of the human body.

Their partnership led to the release last July of CheckLight, a soft, flexible skullcap with integrated motion sensors that measure the force of impacts to the head with a high degree of accuracy. The sensors are embedded in a stretchable plastic material and work in conjunction with an array of electronic componentry, including flexible metallic interconnects that are linked to a microprocessor as part of a system that analyzes, stores, and communicates crucial information about the severity of head impacts. CheckLight uses sophisticated algorithms to analyze and interpret the impact data, indicating the severity of a blow to the head via the activation of a green, yellow, or red LED light. 

"CheckLight takes the guesswork out of identifying how hard you just hit your head," said Litchfield in an interview at CES. "And that's super important because if you and I were downhill skiing right now, and you come across me and I'm flat out in the snow, and you're like, 'Hey, Paul, you fell—are you OK?' And I'm like, 'Yeah, my knee is OK, my ankle and my shoulder are OK. Did I hit my head? How hard did I hit my head? Am I OK?' And so what CheckLight does is it takes the guesswork out of trying to assign a force value to the impact that just occurred to your head. That might seem like a simple statement, but it's incredibly powerful, and it was the missing part that we focused on when we began to really explore the notion of this CheckLight product."

It's important to eliminate the guesswork, Litchfield said, because when people sustain blows to the head, they're often not aware of the severity of the hit and, therefore, may not seek treatment. Many choose not to talk about symptoms, believing that they will eventually subside without any ill effects. Although it's not a diagnostic tool, CheckLight communicates an objective measure of the force of impact to let people know whether or not they need to be assessed by a physician. The goal is to get people on a quicker path to assessment, diagnosis, and medical support or treatment.

The product launch coincides with a growing conversation in the national media today about the health consequences of concussions and traumatic brain injury, including those resulting from sports-related activities. When Litchfield was growing up, the idea of "getting your bell rung" was viewed as no big deal; it was just a matter of shaking it off and getting back in the game.

"That was the standard operating model," he said. "These days, we're finding out that that's not the right way to go. So, as the medical community is learning more and more about head injury and its acute and chronic long-term ramifications, we're saying that, with CheckLight, any time you get a yellow light, or any time you get a red light, just get yourself checked. It can be really informal, but just make sure you get checked. You shouldn't ignore impacts to your head at a moderate or a severe level. For as tough as these young athletes are, there are certain parts of our body that you don't want to get injured, and I think your brain is one of them. So it's really important to be informed."

How CheckLight Works

CheckLightTM, designed for athletes of all ages and skill levels, is described by Reebok officials as the first impact indicator that comfortably fits wearable electronics directly on the athlete, rather than on the athlete's protective equipment. The key to it all is MC10's conformal electronics platform, which accomplishes what flat, inflexible circuit boards cannot—conform to the curves of the human body in a way that doesn't distract the wearer.

The skullcap is made of a typical apparel knit material, "a polyester material that's got some Lycra in it," said Litchfield. "It stretches, it's comfortable, it's low profile."
Photo courtesy of Reebok

The skullcap is made of a typical apparel knit material, "a polyester material that's got some Lycra in it," said Litchfield. "It stretches, it's comfortable, it's low profile." The electronics are packaged up with a thermoplastic urethane (TPU) material with a rubber-like feel. "It stretches, it moves, it's compliant, it's waterproof," he said. "So the outer shell is a very, very soft and supple plastic that creates a waterproof environment, but also creates a low-profile, very comfortable overall product."

Litchfield described CheckLight as "a kind of New Age skullcap" that's intended for both contact and non-contact sports and activities, including those in which participants traditionally don't wear helmets. The product has been tested on athletes participating in a wide range of sports, including football, boxing, ice hockey, lacrosse, and rugby. "It's used in everything from professional team sports all the way through to individual sports, from cycling and skateboarding to snow sports and motor sports," he said.

Embedded in the skullcap is a piece of electronics that has a little tip and a tail. The tip goes inside a little sleeve on the skullcap, and the tail fits into a little pocket that hangs down the back of the wearer's head. "When you put the skullcap on, the tail of the product hangs down beneath the helmet right in the back of your neck, and the tip goes right up, with the accelerator and gyroscope on it, right behind your left ear," said Litchfield.

A system of green, yellow, and red LED lights alerts the wearer and those around them to the severity of head impacts. When the green light is on, it means that the device is on and functioning; you have not sustained a moderate or severe hit. The yellow light activates when you incur a moderate level hit, and the red light indicates a severe hit. Litchfield said that the hit criteria used by CheckLight are based on the same head injury criteria from Wright State University that are used by the National Transportation Safety Board. 

"Much like a traffic signal, if it's green, it's go; you're all set. If it's yellow or red, it's caution and stop," he explained. "And so the yellow and red lights are intended to make sure that you get assessed—get yourself on a pathway, whether you're with friends doing something casually, or whether you're in a formal, organized sport. Make sure you have the coach, your parents, the trainers, or whoever, just check you out. More often than not, you're going to be fine, but if you're not fine, you really should get on the pathway to assessment and recovery as quickly as possible."

CheckLight measures more than straight-on impact, according to Litchfield. Inside the device are an accelerometer, which measures acceleration and deceleration that occurs linearly, and a gyroscope, which measures acceleration and deceleration rotationally. Both are needed, Litchfield said, because a linear force of impact—a straight-on hit to the forehead, for example—causes a different type of injury from that caused by a rotational force of impact, such as a glancing blow to the temple.

 "By putting both of these devices in there and by having them activate at the same time, it makes this a much smarter device because it will consider, electronically, both the linear aspects and the rotational aspects of an injury and 'bucket' that output in the appropriate value," he said.

Once the gyroscope and accelerometer are activated, the device looks at the peak activation, it looks at the time of activation, and then it then calculates where—based on nine locations around the head—the hit has come from. CheckLight employs sophisticated algorithms that account for the fact that head impacts are absorbed differently in different locations: A person's neck and supporting musculature, for example, may allow them to absorb more impact in a straight-on hit to the head than they'd be able to absorb in a blow to the temple, which would likely involve a rotational force. "The device is super smart and the algorithms are super sophisticated," said Litchfield.

Innovative Design Features

MC10 (, a Cambridge, Mass.-based startup whose investors include North Bridge Venture Partners, Braemar Energy Partners, and Medtronic, among others, is on a mission to "extend human capabilities by making high-performance electronics virtually invisible, conformal, and wearable." The company's handiwork, based on the stretchable electronics platform of technical co-founder John Rogers, a professor of engineering at the University of Illinois, Urbana-Champaign, is evident in CheckLight's unobtrusive form and fit.

"What's really innovative about the product is that we designed it to be, essentially, transparent when you use it," said Litchfield. "When you put this on, all you feel is your traditional skullcap underneath your helmet. You can't feel the device; it just essentially becomes invisible when you use it. And what's really cool about it is that it's very apparent and very evident when it works. So there's a transparency in its fit and form, but its effectiveness is absolutely apparent."

CheckLight's electronics are packaged in a thermoplastic urethane (TPU) material with a rubber-like feel
Photo courtesy of Reebok

Another important aspect of the design is that CheckLight is not intended solely for football or for ice hockey, or for lacrosse or baseball, he said. It's not a device just for bicycling, or snowboarding, or for skateboarding or equestrian events, or for motorsport events like motocross. "It's really a device for all of them," he said. "What's great about it is that it's designed in a way to be universally available to any sport or activity you're doing.

"The other thing that's really cool about this device is that it will retain, in its memory, the number of  yellow and red hits that you've incurred," he continued. "And in the growing body of knowledge in the medical community, it seems there's a direction heading towards being concerned about the number of hits you take over a long period of time. So this device will actually measure those outputs and keep a record of those outputs."

The genesis of what is now CheckLight goes back about four years, when Litchfield and CheckLight Program Director Paul Davis were aware of a small and growing conversation about head trauma and were determined to get involved. They were interested in finding ways to help reduce the incidence of concussions. 

"We quickly found out that the only way [to stop them from occurring] is to have people stop playing anything and stop moving around, and that's not realistic and it's kind of silly," he remembered. "So then we started talking about how we could get at more information about impacts."

That question got Davis, Litchfield, and their Advanced Concepts team off and running, leading to what Litchfield called "a colossal education" along the way. It's been a profound learning experience, he said, not only in the "absolute aspects" of head impacts, devices, and electronics, but also in some of the "less than clear issues" that currently exist in the medical community and elsewhere. "It's been an evolving process, both from the background of the head trauma issue and from the device," he said.

Litchfield is on the board of directors of some companies that were helping with a particular product that benefited from conformal electronics. Through networking, he was able to hook Reebok up with MC10.

"The collaboration with MC10 has been great," he noted. "MC10 does flexible conformal electronics, and they do it really well. It's a super talented group that came to the table with us; we kind of forged this integrated team and we rolled forward as one group. MC10 provided the electronics backbone and we provided the form factor, the design of the device. It's a great relationship. The MC10 crew is a very, very talented group.

"One of the things that we strive to do in Advanced Concepts at Reebok ( is we strive to make sure we continually look out in the world at people who are doing cool things that can help educate us and challenge us in our thinking," he said. "I've been working at Reebok for about 28 years, and you can get pretty set in your ways. And what's super important is you've got to keep on challenging yourself to kind of think differently."

A Potential Teaching Tool

Having been in development with CheckLight for about four years, Reebok has tested the device on "hundreds of athletes in a number of different test cycles," and in a variety of sports, according to Litchfield, who said that it's been gratifying to know that the product has already helped people.  

"In our testing methodology, some people have gotten yellow or red hits—not the big, open field, 'knock 'em out' kind of hits, but just regular, in-play hits and contact," he said. "And they've been assessed and diagnosed and, most times, put right back in the field of play. But a couple of times, people were injured and they got the appropriate medical support right away. And that allowed them to recover and get back on the field of play sooner."

Litchfield sees CheckLight as a potential teaching tool that's changing the way people participate in some of the high-impact contact sports. The device is actually helping to reinforce safer contact techniques by encouraging athletes to keep their heads up and out of impacts. Because athletes will know that they'll have to come off the field if their yellow or red light goes on, they're finding ways to make sure their head doesn't absorb the biggest hits on the field. 

"This is anecdotal; this is not the principal use of the device, but, anecdotally, throughout our testing and throughout the use, the people using CheckLight have been using it in a way that they've taken their head out of their first contact because they don't want the red light to go off," he said. "So what it's doing is it's kind of changing the way people participate in some of the high impact, contact sports, because you can still play well and do a great job, and if your yellow or red light doesn't go off, you're going to stay on the field. So it's been kind of cool. Hopefully, this will ultimately be considered as a potential teaching tool on how to teach people to participate in these high velocity, high impact, high contact sports, and for finding ways to make sure your head stays out of the principal hits."

An Extra Set of Eyes for Coaches

CheckLight, designed  to be worn by people participating in all types of sports and activities, is nevertheless a natural for high-impact contact sports, such as football and boxing. We sat down with Paul Litchfield, vice president of Reebok's Advanced Concepts Group (RAC), earlier this year at CES in Las Vegas, and asked him about the company's plans for CheckLight.

Q: Do Reebok's target markets for CheckLight include college football, the NFL, and professional boxing?

A: Yes, they sure do, and I suspect that those will be people who endorse and support it, but I'm not sure that they will be the first users of it. I actually think it's going to be people like you and me, with our families, with our kids, as we are living our life. Professional sports are an interesting perspective because these folks are getting paid to stay on the field. Their careers, their income depends on it. They also have multitudes of people looking at them at every play. And so do college athletes. They're being evaluated all the time by the coaching staff, by the medical staff, by the training staff. So they certainly could benefit from using CheckLight, but I'm probably more concerned with helping out the youth, the kids, the Dad doing soccer practice, or a Mom doing hockey practice. The coaches can't see all the plays, and they're not there to be diagnostic of what kind of physical maladies are occurring; they're just trying to help the young kids out.

And so CheckLight is a great tool to give them an extra set of eyes, and to put a value to the impacts that may occur that are going to occur anyways. That way, you can be just a little bit more confident, and you can focus on the play, as opposed to worrying about the health of the kid.

Q: What do you see as the company's biggest challenge in achieving broader market adoption of CheckLight?

A:  We're going to need, at the consumer level, just a mind shift, and I'll give you a couple of examples. When you and I were growing up, did you ever wear a bicycle helmet or a seat belt? No. I never did, either. They were available, and yet nobody used them. But people have used bicycle helmets more and more, and now, when you see somebody riding a bicycle without a helmet, you're like, 'That's kind of strange.' And seat belts, everybody wears them now. The most recent kind of example I can give is in snow sports—downhill skiing and snowboarding. Five years ago, you would see a couple of helmets on some people, and you'd assume they were ski racers. Nowadays, I bet on any ski hill, there are probably 90 percent of the people wearing helmets. So it's basically a mind shift to people understanding what the value of being informed about head impact can provide. And we're working real hard at that.

This technical information has been contributed by
Reebok's Advanced Concepts Group

Home |  About Us |  Back To Technical Library |  Contact Us
Copyright © 1996-2010 All Rights Reserved.
General or Technical Questions? E-mail