Software Sees Individual Muscle Motions
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New muscle-modeling software could allow for more informed treatment of physical disabilities and provide insight about how humans and animals move, information that could also lead to more natural robots.
When muscles are activated, they generate forces that pull the bones they are connected to close together, said Jen Lee Hicks, a Stanford University bioengineer now leading the software's development.
You cannot tell what these forces are by just watching someone move or even recording motion-capture data [with cameras and reflective markers], since the human body is so complex. This is what simulation allows us to explore.
Previously, researchers interested in noninvasively observing muscles were limited to studying those near the skin, Hicks said. Another problem is that this method could only show when muscle is active, not the forces required to move it during an observed motion.
"These approaches [also] do not let us explore individual muscles forces and they make it more difficult to ask what if questions, like what happens when a muscle become stronger or weaker or we use an assistive device, Hicks explained.
The new software, called OpenSim, relies on multiple cameras to capture the location, velocity, and acceleration of reflectors pasted on a moving body. Using well-established rules from physiology and physics, the software then simulates that motion. Even though the reflectors are pasted on the outside of a body, their motions relative to each other in 3-D space, combined with the musculoskeletal model, provides enough information for OpenSim to create an accurate simulation of a person's movements and calculate the required muscle forces, Hicks said.
The software's ability to provide a dynamic, holistic view of muscle interactions could help in the diagnosis of muscle-related health problems and prevent unnecessary surgeries. For example, when OpenSim was used to analyze data from children with cerebral palsy a neurodisorder characterized by a crouched, irregular gait the software showed that in some cases, the deformity was due to a bone in the lower leg rather than the tibia bone in the upper leg, which is the usual culprit.
The bone in the lower leg had a big impact, because of the dynamics in the body, on what the muscles in the hip were doing. So that's something you wouldn't tease out, without this model, that incorporates the three dimensions of the human body, Hicks said.
First publicly released in August 2007, the free open-source software has been used by scientists for a variety of other purposes, as well. An Italian group designing robots that walk like humans uses the software to fine-tune the machine's musclelike actuators, while a researcher used it to model the running gait of a T-rex.