When the Military Advanced Training Center (MATC) at Walter Reed Army Medical Center in Washington, D.C., opened last September, it met a long-standing clinical need that has become increasingly urgent: the need for an integrated facility to rehabilitate returning soldiers who had lost limbs, suffered impaired limb function, or sustained brain injuries in Iraq and Afghanistan. The two-story, 31,000-square-foot center includes offices for counselors; a family lounge and kitchen; prosthetics fitting rooms; a climbing wall; and a ceiling-mounted exercise track that lets patients, wearing a harness, walk or run without being tethered to a therapist. The MATC even has an immersive virtual environment where patients, standing on an interactive platform, can test their reflexes.

Besides showcasing the latest technology, the MATC gathers into one place treatment areas that previously had been scattered around the hospital. One of these areas was the Center for Performance and Clinical Research, known as the Gait Lab, where physical therapists and biomechanical engineers study patients' motions as they walk to gauge how rehab could help them and ensure they're using the right prosthetic device with a good fit.

The old Gait Lab was a retrofitted square room, 28 feet by 28 feet, with eight special motion-capture cameras mounted on the walls and staff desks in the corners. There, the actual walkway for patients was about 25 feet long “at best,” says Brian Baum, a Gait Lab biomechanist. Patients in the later stages of rehab, able to take fairly large, quick steps, had to stop short. There were other drawbacks, says Baum: “We did struggle with vibration problems … we were next to prosthetics, where they use their big machines to fabricate prostheses. There was tons of sawing.”

So when Congress approved $10 million for the project in 2004 and—after a false start by another firm, whose design came in over budget—the project was awarded the following year as a design/build to Turner Construction Co. and Ellerbe Becket, Baum and his colleagues had the chance to draw up a wish list for their new lab. They wanted the lab to sit on an isolated slab of concrete, so that vibrations from surrounding rooms wouldn't affect their patients' motions (or how they calibrated them). They wanted more space, so patients could walk briskly, even run. They wanted a higher ceiling, so cameras could be mounted higher up to give a bird's-eye view. And, last but not least, they wanted better equipment.

Pouring the isolated slab was the crucial first step. “We designed a special floating slab for the [virtual environment] area and the Gait Lab, dropped down about 6 feet,” says Tom Anglim, director of government services at Ellerbe Becket, who served as its project director on MATC. The extra space was needed for the six force plates that were installed in the floor to register how patients carry their weight as they walk, as well as for a treadmill with two more plates (the old lab had only two in total). This floating slab “does have a soft gasket material around the edge to keep it from contacting the rest of the concrete,” Anglim notes. The dimensions of the new room were set at 48 feet 10 inches by 34 feet 5 inches, with an 18-foot ceiling, says Baum. “Size and ceiling height are, from an architectural standpoint, basic things, but they afford us so much more flexibility,” he says.

The new Gait Lab takes the 19th century stop-motion photographic analysis of Edward Muybridge into the 21st century.
Corbis The new Gait Lab takes the 19th century stop-motion photographic analysis of Edward Muybridge into the 21st century.

When it came to specifying the new cameras, computer hardware and software, and force plates, the Gait Lab technicians were in the driver's seat from the beginning, says Elihu Hirsch, who was the project manager for the U.S. Army Corps of Engineers, which partnered with Turner and Ellerbe Becket on the center. “Brian and Barri Schnall [a Gait Lab physical therapist] would sit in on our design reviews and comment on what they needed,” Hirsch recalls. “[They] had been shopping around for cameras and technical equipment. They told us what the requirements would be as far as control wiring and wiring to cameras and computer monitors—they were able to communicate that to us with a sketch.” It was not just desirable that the Gait Lab be planned around the equipment, says Hirsch; it was essential, or it wouldn't perform effectively: “It was very, very critical that when the equipment was set in place, we didn't have any change in elevation. If someone is running to where the force plates are, it's very important they don't experience any tactile difference. We had to make sure the equipment would be integrated into the final construction.” The 23 cameras in the new lab are, unlike their eight predecessors in the old lab, mounted to an aluminum truss system that can be adjusted up or down (though “moving them is not the easiest thing in the world,” admits Baum). Baum and his colleagues chose motion-capture cameras of a type commonly used in medical applications and also in the movie industry for animation. The model used in the Gait Lab is the Vicon MX-F40. “Each camera has a strobe of LED lights around it that flash a particular frequency,” explains Baum. “Every time they flash out, the flash hits a marker [on the patient's body] that's covered in special reflective tape. If the strobe flashes out 120 times per second, we can get the position of a marker in that camera view every 120th of a second.” With 4-megapixel as opposed to 1.3-megapixel resolution, the new cameras are a big upgrade from those they replaced. “They allow us to see the same-sized marker farther away or use much smaller markers at the same distance—we can model motion in a lot more detail,” Baum says.

Each camera has a cable that leads to an area with three hardware boxes where the cameras plug in, eight per box. (The 24th plug is the one that connects the force plates.) Those boxes share one connection to the control computer. That computer uses a software program, also made by Vicon and called Nexus, to capture the 2-D views from the 23 cameras and turn them into a single, composite, 3-D image of where all the markers are in space. Did the technical requirements for such detailed motion capture make it an especially difficult project? Not really, says Anglim. “There did have to be inserts in the walls and structural supports” for the truss system, he says, and there was a lot of cabling. But it didn't drive up costs very much, and besides, he says, “Our staff really enjoyed working on it because of some of the complexities.”

Baum is excited about the new lab's research potential. “We're in the process right now of collecting both our patients' data and uninjured control [group] data,” he says. With the longer walkway, people walk faster, Baum has found: “We get a better sense of what a truly comfortable pace is.”


Cameras: 23 Vicon high-speed digital motion-capture cameras, model MX-F40, vicon.com
Software: Nexus, manufactured by Vicon and touted as “the first Life Science–specific motion capture software on the market,” vicon.com
Hardware: The Gait Lab staff use two PCs. The primary PC runs the Nexus 1.3 software that controls the motion-capture system. This PC has two Intel Xeon 5130 processors running at 2.0 GHz, with 2.5 GB of RAM and an NVIDIA GeForce 7600 GT graphics card with 256 MB RAM. The other PC is dedicated to the lab's two high-speed digital video cameras (different from the motion-capture cameras). It has an Intel Core2Duo processor running at 2.4 GHz with 2 GB of RAM and an NVIDIA GeForce 7600 GT graphics card with 256 MB of RAM.
Aluminum truss system provided by LA ProPoint:lapropoint.com
Force plates and treadmill provided by AMTI Engineering Services:amti-es.biz

Project Credits

Owner Walter Reed Army Medical Center, Washington, D.C.
Owner's rep U.S. Army Corps of Engineers Department of the Army
Architect Ellerbe Becket
Engineering services Dynamic Corp.
Geotechnical engineer Haley & Aldrich
Structural engineer Weidlinger Associates
General contractor Turner Construction Co.