Just Moving Along

Researchers at East Carolina University’s biomechanics lab use motion capture technology to study the how and why of how we move.

GREENVILLE — Sidney Chadwick is a senior at East Carolina University who likes to run. It’s fun, she says, and it’s also good exercise.

This day finds her running, but only from one end of a room to another. It’s a distance of about 30 feet. Not much exercise, she admits, but it’s still running for good health.

“It’s interesting how we can change the way we move and we do it to move better," Chadwick admits, as she laces up her running shoes. “That’s a lot of what we are doing in the lab, looking into ways to improve performance and prevent injuries.”

The lab Chadwick refers to is the biomechanics lab at East Carolina University in Greenville, North Carolina. Biomechanics applies the principles of mechanics to understanding living organisms. In other words, to study the structure and function of a biological system through the methods applied to a machine. To do that, Chadwick is transformed from a runner to a human sensor.

"The body is pretty amazing and that’s why we’re here, because we love human movement,” says Dr. Paul DeVita, director of the biomechanics lab. “And applying physics to human movement is challenging, fascinating, and ultimately, we hope, it will produce information that will improve quality of life.”

The centerpiece of the lab is the testing platform, which is surrounded by eight high-definition cameras. The cameras are arranged to record the test subject from every possible angle. Chadwick has 38 infrared sensors attached to her arms, legs, upper and lower torso and her feet. Three-dimensional motion capture technologies will record her as she runs across the platform.

“Three-dimension movement and 3-D recording more accurately capture what we do because we move in three dimensions,” explains Dr. DeVita. "In addition, the forces that affect our bodies come to us from all directions, so if we are studying those forces, we need to get the most accurate assessment of human movement.”

Once Chadwick is outfitted with sensors, she is told to run across the platform multiple times. She is also told that one foot needs to land squarely on a gray box in the middle of the platform. It’s a sensor plate, which measures the amount of force with which Chadwick’s foot strikes the plate.

The result of the experiment is a dotted figure that runs across the computer screen. There is no body outline. The location of the dots resembles the rough outline of a body. If you triangulate the dots you can estimate the location of limbs and joints.

As the dotted body strikes the force plate, arrows extend upward from the plate showing the amount of force the body feels when the foot strikes the plate. The force grows even stronger as the runner’s foot pushes off to continue the stride.

“The really exciting part comes next, when we use biomechanical calculations to understand the forces,” says Dr. DeVita, as he watches the dotted runner moving across the bank of screens facing the testing platform. "For instance, we can calculate the forces in the ankle, knee and hip joints, the forces in ligaments in those joints, and the muscles surrounding those joints. To do that, we need to measure the force outside, but what’s really important for health are the forces on the inside.”

The information from those force calculations is used to create more effective training programs for athletes to prevent injuries as well as better rehabilitation programs to help patients recover from injuries.

Take, for example, if researchers are working to understand an injury mechanism related to cartilage. Force calculations might be performed to understand the stresses that are acting on the tibia and femur, or the patella and the femur. To make those calculations, researchers would use the 3-D position data during running as well as study the ground forces under the feet.

Here’s the another example. If researchers wanted to analyze the stress or strain on a bone in the leg, they would use the 3-D modeling to look at the geometry of the bone from images as well as the forces under the feet.

“With our models, we can calculate the strain on muscles, the pull on bones and the multiple tensions pulled from all sides of a particulate joint in the body,” says Dr. John Wilson, associate professor in the Department of Physical Therapy. "The three-dimensional motion capture technology is the foundation for all of this math.”

Dr. DeVita puts it this way, "Each view provides different information and we use the total of all views to get the total understanding." 

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