New technique gets under people’s skin

Amanda D. Francoeur, amanda.francoeur@laurin.com

Researchers have designed a real-time imaging system that could advance physical rehabilitation for soldiers, athletes and others who need to retrain their muscles. The passive optical motion capture system, using reflective markers positioned at key points on the body, collects data on muscle movements, while HBM (human body model) software integrates it into an existing skeleton prototype and analyzes the forces that the muscles generate. The result is a real-time virtual body double showing the musculoskeletal system in motion.

A digital representation of a human model is shown, with muscles at rest depicted in red and muscle force activity in green. The graphs indicate which muscles of which leg (right or left) are moving and the force generated. Courtesy of Motek Medical BV.

It’s the “beginning of a road to the future,” said Michiel Westermann, CEO of Motek Medical BV, which designed the system. Westermann believes that the technology is as effective for real-time viewing of muscle forces and joint torques as MRI is for tissue density and that, in the future, it may replace electromyography, which measures the electrical activity of muscle movement.

Seeing double

During the movement analysis study, the subject walks or runs on a self-paced, interactive instrumented treadmill called the V-Gait system, which includes sensors measuring muscle output and joint load. “When walking, you can measure each ground reaction force of each foot separately,” Westermann said.

The individual wears a suit with 47 reflective markers, each at a joint’s center of rotation. A minimum of eight high-resolution infrared cameras operating at 120 Hz surround the treadmill setup, and infrared lights illuminate the markers.

Previously, muscle forces generated were invisible to the eye, but the HBM software incorporates known external movement and forces with internal forces and displays the transference of force as it occurs. An inverse kinematics function determines joint position and orientation; accelerations and forward dynamics are calculated, also.

The HBM software integrates data from the reflective sensors onto a human skeleton prototype. Courtesy of Motek Medical BV.

The individual can see how his muscles respond to a motion he makes, so he can either repeat the movement or correct it, as well as adjust imperfections in his posture.

Currently, the imaging system is used primarily to analyze motion of the knees and lower back, sports-induced fatigue and balance, but researchers are in the process of adding an upper-body analysis function. Motek is developing the system so that it can be customized to the individual, allowing patients and doctors to focus on a specific muscle without having to visualize the entire body. Specifically male, female and child models are being created, too. The company hopes to prove that the HBM technique equals or surpasses electromyography. The system may be available in the US at the end of 2009.