Seeing Inside the Human Machine

UNC-Charlotte researchers apply motion analysis to study how the body responds after injuries, surgeries and rehab programs.

CHARLOTTE — It’s a pretty simple act: stepping up and onto a block, stepping down and then stepping up again. The block is only about one foot high. Dr. Nigel Zheng is demonstrating to a student what he wants to see.

“Step up, then on one leg squat just a bit, then step down,” Zheng says, and he goes through the motion. “It’s not high, but just balance slowly.” 

Dr. Zheng is an associate professor of mechanical engineering and engineering science at the University of North Carolina at Charlotte. And in the University’s Motion Analysis Lab, the professor has an entirely different view of this simple act of stepping. He’s developed a way to look at the body as a collection of simple machines, which are defined as mechanical devices that change the direction or magnitude of a force. Simple machines include levers, pulleys, incline planes, wedges and screws. By viewing them this way, researchers can study the forces acting on, through and around the parts of the body. 

“Our computer models capture and calculate different exercises, so we can see which exercise has high force and high stress on the joints,” says Dr. Zheng. 

To see inside the human machine and better understand how it works, requires dozens of tiny sensors on the body: 10 cameras recording images at 240 frames per-second in a real-time motion capture system, force plates on the floor, a body scanner and lots of computing power. 

That technology translates into an image of a tiny stick figure on a computer screen. But as the screen figure mimics the motions of the real subject in the lab, red arrows highlight where the greatest forces are showing up on the body. That includes the strain on the knees, the impact of a foot striking the ground or the torque on a hip joint, just to name a few. 

The data is being used to evaluate patients before and after injuries, before and after surgery, and before and after a specific training or rehab program. 

“The human body has biofeedback, and everybody is different, and they heal in different ways," explains Dr. Zheng. “Something that works for one person may not work for another person, and that holds true for different surgical techniques, different exercise and different rehab programs.” 

Take running for example. 90 percent of all running injuries aren’t caused by running. They are caused by a biomechanical error between heel-contact, shock absorption, adaptation, mid-stance and propulsion. 

The analysis of forces, balance, impacts, stresses on joints and power in muscles helps runners develop sound mechanics to avoid injury.  The analysis is also used to develop exercises to strengthen weaker areas of the body. 

“We bring a person in the lab and have them run just a bit, and we can see how much they are leaning in one direction,” says Dr. Zheng. “We can also see the angles, the angle velocity, how much time they spend on one leg or the other." 

The goal of the analysis is to quantify things that you can’t see in the clinic or even on video. The runner’s gate may visually look fine, but an analysis of the inner workings of the body can provide a lot more data. 

The same holds true after an injury. Technicians in the lab are working with surgeons to study the effectiveness of surgical procedures, including the fixation of implants and the strength of repairs. Researchers can also better understand how well therapies are working. By studying the body’s movements, a technician can determine what is the best exercise for training and/or recovery after injury. 

The lab performs 20 different tests on subjects, ranging from walking and standing to climbing and getting out of a chair. Those simple moves produce volumes of data and answers that are meaningful. 

“We collect a massive amount of data through those exercises and so we then try, using our algorythyms, to find new knowledge from massive medical data,” says Zheng.

With this technology, researchers and students can look beneath the surface. As students at UNC-Charlotte learn to use the computer modeling system, they're empowered to better find health problems, and therefore solutions.

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