But now, he adds, "DARPA is taking the technological excuse off the table." The goal of the DARPA program was to show that it was possible to build a specific kind of exoskeleton: a wearable robotic system to help soldiers carry heavier loads—possibly double the 50 kilograms an unaided soldier is expected to be able to carry—and march faster and longer. It was important to DARPA that the strength not come at the expense of agility: while wearing an exoskeleton, soldiers would still have to be able to crawl under barbed wire, hide in trenches, and go over steep obstacles. But with the suits, they could also carry more weapons, armor, and supplies, as well as go places not accessible to trucks or even tanks.

Main says the new systems by Berkeley and Sarcos showed that it was possible to meet DARPA's requirements. The two teams, he adds, will now have the chance to collaborate with Army research groups to transform their prototypes into real military tools, which could be in field trials within five years.

That's not to say the civilian applications aren't already tantalizing U.S. and Japanese researchers. There are no reliable projections of the commercial potential for exoskeletons, but a 2004 study by the International Federation of Robotics and the U.N. Economic Commission for Europe estimated that accumulated sales of service robots from 2004 to 2007 could reach nearly $10 billion. Service robots, unlike industrial robots used in factories, are designed to interact with people and help them accomplish certain tasks. They include vacuum-cleaning bots, entertainment humanoids, bomb-disarming rovers, and other systems, which soon may well include exoskeletons.

Japan, with almost half the world's nearly 1 million industrial robots, is likely to be the place where adoption of exoskeletons will first take hold. The country's rapidly aging population—one in four Japanese will be 65 or older by 2015—and its ambivalence toward admitting foreign laborers have created a shortage of caregivers, and some believe robotic-aided nursing care could be the solution.

Over the last couple of years, Japanese companies have demonstrated a number of exoskeleton-type systems for a variety of applications, some serious, some almost whimsical. For instance, Toyota Motor Corp.'s 200-kg i-foot, which looks like a futuristic chair supported by a pair of legs, walks and climbs stairs, but the wearer has to weigh less than 60 kg. The 3.5-meter-high, two-armed bulldozerlike Enryu, from the small robotics company Tmsuk Co., was built to rescue people from burning or collapsed buildings. More fanciful than functional, the 3.4-meter-high, 1000-kg Land Walker, from Sakakibara Kikai Co., shuffles about at 0.4 meter per second and shoots rubber balls from guns mounted on either side.

But those machines aren't true exoskeletons. They carry passengers inside enclosed structures and don't map directly onto a person's anatomy. In other words, they aren't the kind of thing you would expect to see in a nursing home helping the elderly get around.

The development of a truly wearable anthropomorphic exoskeleton was the goal of Yoshiyuki Sankai when 10 years ago he started working on HAL, the Japanese system that will be available in November. Sankai, a professor at the University of Tsukuba, 60 km northeast of Tokyo, says HAL (short for Hybrid Assistive Limb) is a full-body suit designed to aid people who have degenerated muscles or those paralyzed by brain or spinal injuries. HAL-5, the system's fifth generation, made its debut this past June at the 2005 World Expo, held in Aichi, in western Japan.

HAL-5's structure consists of a frame made of nickel molybdenum and extra-super-duralumin, an aluminum alloy used in the wings of Japan's famous World War II Zero fighter planes. Further strengthened by plastic casing, the metal frame is strapped to the body and supports the wearer externally, its several electric motors acting as the suit's muscles to provide powered assistance to the wearer's limbs [see photo, "Bionic Body"].

This newest model improves on earlier versions of the exoskeleton in several ways. Previous prototypes helped ailing humans to stand up, walk, climb stairs, and perform a range of other leg movements—one user was able to leg-press 180 kg (almost 400 pounds)! HAL-5 goes a step further by incorporating an additional upper- body system that helps users lift up to 40 kg more than they normally could. Wearing the suit, a healthy adult male can lift 80 kg, roughly double his typical 30- to 40-kg capability.

"But a human would quickly become tired holding a heavy load," Sankai points out. "This machine can continue holding a heavy weight for 5 or 10 minutes, no problem," he adds, speaking from his office at Cyberdyne, which he set up as a venture company on the Tsukuba campus to commercialize the suit.

Another major improvement is the elimination of the bulky backpack used in HAL-3, which contained the Linux-based control computer and a Wi-Fi communications system. Those components were shrunk to fit into a small pouch that is now attached to the belt. The suit is powered by both nickel-metal hydride and lithium battery packs. Currently, a full charge lasts for 2 hours and 40 minutes, with both the upper- and lower-body parts in action. HAL-5 weighs about 21 kg, but Sankai says wearers don't notice the suit's weight, because it supports itself.