Seeing Inside the Human Machine

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. 

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