The human body is accompanied by a mind and many would say a soul, but it is fundamentally a machine. And so, bioengineering and mechanical engineering Professor Scott Delp reasoned several years ago, it should be simulated on a computer, yielding new insights that doctors and researchers could use to help the disabled, the elderly and even healthy athletes move better.

“We wouldn’t think about designing a helicopter or an airplane without first simulating it, but we design surgeries and medical devices without simulation tools,” he said. “The reason we haven’t had them is they are hard to develop. But just in the last few years we have been able to understand the physics of biology well enough to implement simulations in computers and use them to study the form and function of biological systems.”

Almost exactly a year ago, Delp and his team of postdocs and students realized the goal of creating software that can faithfully simulate the biomechanics of human motion. He released a freely available program called OpenSim, creating a community of about 1,000 registered users. They employ the program as a research platform, a clinical tool, and even to teach principles of biomechanics to high school students.

OpenSim is both intuitively visual and scientifically precise, giving users an easy but powerful tool for determining the forces that muscles and bones exert and endure during most any kind of motion. Users can specify a wide variety of initial conditions, such as the position and orientation of bones and muscles, and the software will animate them according to carefully modeled physics tuned by real measurements. Like any physically validated simulation, the software allows researchers to run useful experiments that would be difficult and costly, if not impossible, to conduct with real patients. But the value to real patients is as clear as the value of having a healthy body.

“OpenSim is designed to examine the dynamics of human movement,” Delp said. “We care about mobility because if you lose your mobility, you lose your health.”

Widely used

For biomechanics researcher Frank Buczek, Senior Investigator at Shriners Hospitals for Children, OpenSim is playing an important role in his effort to develop a mathematically optimized model of the gait of children. The research, funded by the Shriners, aims to replace a gait model that was developed in the 1960s using what would now be considered antiquated technology and correspondingly inadequate mathematical detail. A better model, Buczek says, would give doctors the ability to predict the outcome of different treatment approaches for children with cerebral palsy, orthopedic problems and other disabilities.

After years of developing his model at the Shriners hospital in Erie, Pa., Buczek is now collaborating with Darryl Thelen, an OpenSim developer now at the University of Wisconsin, to test whether the new model is indeed more accurate than the conventional gait model. In these tests, OpenSim acts as a third-party, objective source of biomechanics data to measure each model against. The data comes in the form of the angles of the joints as well as the forces and powers one observes in those joints during a particular motion.

“We look at the same set of data coming out of our model and the old model and see how often ours comes closest to [OpenSim’s] simulated truth,” Buczek says.

Word of OpenSim continues to spread and the number of users continues to increase. An Aug. 5 seminar on OpenSim at the North American Congress on Biomechanics in Ann Arbor, Mich., drew over 100 people. A late August user “jamboree” marking the software’s first anniversary at the end of August was filled to capacity.

Delp, of course, uses the software in his own biomechanics research and he’s made some interesting findings regarding the muscles that contribute most to walking speed, and how that changes as people age. The National Institutes of Health have funded a study of the subject with an eye on preserving the mobility of an aging U.S. population.

“We’ve discovered that the main muscles that propel you forward and help you maintain speed are your calf muscles,” Delp says. “Even in healthy elderly subjects those muscles may be substantially weakened. It’s a simple exercise paradigm to maintain the strength of your calf muscles and by doing so you can maintain the normal mechanism for propelling yourself forward.”

NIH was instrumental in OpenSim's creation. The software is a project within Simbios, an NIH funded center at Stanford dedicated to applying computation to biology and medicine.

Teaching tool

While researchers were hard at work with OpenSim in the lab this summer, a younger crowd was boning up on the basics of anatomy and physics using OpenSim as part of Stanford’s Educational Program for Gifted Youth. The biology class of about a dozen 10th and 11th graders, taught by mechanical engineering graduate student Sanjay Dastoor, focused on the dynamics of the body. Students, for example, used the software to see how the relocation of a tendon, such as a surgeon might attempt, affected the range of motion of the wrist.

"I could explain the concept in class, but they understood it much better when they were interacting with the simulation," Dastoor said. "The students could insert the tendon in a variety of locations and see where the surgery would be beneficial and where it wouldn't."

Delp now has a new grant from Stanford’s K-12 education initiative to bring the software to other high schools. In that case, OpenSim’s mission will be to turn kids onto physics by making it virtually come alive. And why confine it just to humans when OpenSim has a Tyrannosaurus model built in?
It’s been a successful first year, which Delp considers but a running start. From here he hopes the software and its community will continue to grow so that the simulation can have a greater impact.