Volgenau School of Engineering
George Mason University
George Mason University Mason
George Mason University

Engineering Students’ Device Helps Athletes ‘Stay in the Game’

August 12, 2016   /   by Martha Bushong

Do you know someone with a torn anterior cruciate ligament (ACL)? If you answered yes, it’s not a surprise. According to NCAA statistics, 1 in 13 female athletes experience a torn ACL. It’s an epidemic that no one is talking about. No one that is, except an enterprising team of students in the Volgenau School of Engineering’s Systems Engineering Program. Even though each of these students is an athlete, the project tested their problem-solving abilities, not their physical prowess.  

Team members Amr Attyah, Maribeth Burns, Sam Miller, and Andrew Tesnow, all systems engineering majors, started by building a simulation model of the knee. They then introduced failure mechanisms—five noncontact and three contact ones. The ACL can be torn through contact (getting hit in the knee) or through noncontact means (turning weirdly or landing a jump incorrectly). This engineering team focused on ACL tears due to low knee flexion angle, theangle between the femur and the shin.

"Everyone thinks ACL tears are the result of contact, but 70 percent are the result noncontact movement, like landing from a jump, stopping short, or moving quickly from side-to-side," says Miller.

Based on the failure mechanisms, the students started to experiment with ways to prevent ACL tears. The whole idea was to reduce the force placed on the ACL from the shank, or shinbone.

"The ACL can only handle 2100 newtons. So anything over 2100 newtons will tear the ACL," says Attyah.

Before the students could solve the problem they had to explore other engineering fields.  

"We had to become fluent in biokinematics and knee anatomy to better understand the problem," Tesnow recalls.

At least six main factors impact the tibial shear force (TSF), so the students looked for ways to address each factor. For example, ground reaction force—the force between the ground and the foot—can be reduced by an energy-absorbing material.

"Even padding in the shoe is not enough," says Attyah.

The students found that form and position of the body while landing, stopping short, and cutting are also key factors. Flexion angle needs to be below a certain threshold. If there is too little, the quadriceps pull the shank forward and the hamstring and calf muscles cannot counteract it. Then the shank slides out from under the femur.

Finally the team proposed coupling angle and acceleration sensors in a knee sleeve with pressure sensors in the shoe. Based on data from the sensors, a tiny microcomputer calculates an estimate of the TSF. When the TSF exceeds a threshold, it beeps to alert the user of the danger approaching.

The goal is to provide athletes with real-time feedback of their body position and form while landing, stopping, and cutting in a game so they can adjust the way they play. This is more useful than gait analysis video in a controlled lab, for which athletes wear special clothing, or form training, in which they jump over cones in a sterile gym.

The simulation model of the biofeedback system seems to be working fine. The students are rapidly developing a prototype and have started their testing.

"This was the hardest thing I have ever done in my life," says Burns, the team leader. "We were so naive when we started. The project kept getting more complex. We ran into dead-ends everywhere we went. Thankfully, our systems engineering faculty provided guidance and encouragement that helped us use our knowledge and skills. I have so much more confidence in myself as an engineer and as a person. And hopefully we can help some athletes stay in the game."