Web Extras: Movie

Walking the Line
By Emily Carlson
Posted August 27, 2008

Quads, glutes, hamstrings, calves—these are all leg muscles that we try to slim down or bulk up by running, biking, squatting, and lunging for hours at the gym.

While we’re busy pumping iron to perfect these muscles, people like Chand John at Stanford University are computationally modeling them to understand their role in walking disorders.

This simulation, developed by John and his colleague Eran Guendelman, shows the activity of different leg muscles during a casual stroll. Red indicates that the muscle has received a signal from the nervous system to contract and generate force while blue indicates that the muscle is receiving no signal.

"With the simulation, you can tell what muscles are 'on' at certain times," says John, currently a graduate student. "This is something that is not well understood—and even less understood in walking disorders."

Injuries or impairments that affect the nervous system can disrupt the signals sent to muscles, sometimes causing abnormalities in one’s step. Knowing how muscles are involved in normal walking could aid the development of treatments to improve speed, balance, and posture.

The movement of this animated skeleton is actually based on measurements taken from a real person. John and others invited a healthy adult man about 6 feet tall to a motion lab for experimental studies. They measured his walking movements by attaching reflective markers all over his body and asking him to walk on a treadmill that recorded the forces exerted by his feet. Video cameras captured all the action.

Use computer modeling to decide the best treatment for a person with a walking abnormality. Download OpenSim, free software for simulating movement and understanding muscle forces, and follow tutorial #1.

John and Guendelman entered this force and motion data into a customized software program that calculated when the muscles "turn on." The end result was this simulation. The project took about a year to complete.

The work is an example of computational modeling that uses concepts from physics—force, acceleration, and energy—to simulate human movement in a particular way. The software behind it is freely available to others studying movement disorders and one day may be used by coaches to improve athletic training.

John, who studied computer graphics in college and is working toward a Ph.D., says he will continue to apply his knowledge in computer sciences and mathematics to investigate the biomechanics of humans, develop more realistic animations, and even create robots that can assist with different physical tasks.

"In computer graphics, the end goal is to make nice pictures," John says. "Biomechanics enables me to have the end goal be scientific discovery and results that are important to humanity."