DALLAS

Wearable machines that enhance human muscle power are poised to leave the realm of science fiction and help factory workers hoist heavier tools, lighten soldiers' loads and enable spinal patients to walk.

Lockheed Martin and Parker Hannifin are joining a handful of start-ups in finding practical uses and, more important, paying customers for bionic suits inspired by novelist Robert Heinlein's 1959 "Starship Troopers" and Stan Lee's Iron Man comic-book character.

Sales of mechanical exoskeletons cap decades of scientific ­tinkering that included a 1,500-pound General Electric clunker in the 1960s. Strapped to users' bodies and powered by lithium-ion batteries, the emerging technology has led to some models that sell for about $70,000, weigh fewer than 50 pounds and are nimble enough to dance the Macarena.

"We're now seeing a golden age in which we can produce this technology and derive benefit from it," said Keith Maxwell, the business development manager for Lockheed's program. "There's a host of ­industries where this works."

The first commercial sale of a medical unit — not for lab or hospital tests — came in September, pioneering a field that may produce $400 million in annual revenue by 2020, according to technology ­consultant ABI Research. Lockheed says it hasn't estimated the value of any contracts for its underdevelopment military version, known by the acronym HULC, or for the nascent industrial market its Mantis device will enter this year.

The machines may follow a ­classic arc from Pentagon research project to fixture on an assembly line, similar to the development of lasers, said Paul Saffo, a managing director at investment advisory firm Discern in San Francisco.

"The medical devices get the most attention, the military funds it and the first mass application is industrial," Saffo said.

Developing technology for both civilian and military use would be a boost for Lockheed, the world's largest defense contractor, as it confronts reductions in U.S. arms spending. Parker Hannifin, the biggest manufacturer of motion and control devices, is seeking to expand into the medical industry.

Ekso Bionics' device for spinal patients looks like the lower half of a black metal skeleton able to stand by itself on foot pads. Parker ­Hannifin's medical model breaks into five pieces and resembles elongated plastic football thigh pads worn on the sides of users' legs.

Electric motors amplify the strength in their wearers' limbs or, in the case of the wheelchair-bound, supply motive power. Computers and sensors help provide balance and guidance.

"There's a huge wave of human augmentation coming," said Ekso Bionics CEO Nathan Harding, whose Richmond, Calif.-based company has devices in operation at New York's Mount Sinai Hospital, the Kessler Institute for ­Rehabilitation in New Jersey and other spinal-cord injury centers. "It's in its infancy."

Argo Medical Technologies entered the market last year, with an exoskeleton to assist patients who have lost the use of their legs. Parker Hannifin's Indego model also targets those users, and will go on sale in 2014 at a price the company says is competitive with Argo's $67,230 unit.

In between those introductions will come Lockheed's Mantis, which the Bethesda, Md.-based company envisions as finding a home in any industry in which workers must hold heavy equipment that can cause fatigue and back injuries.

Mantis has a mechanical extension for a wearer's arm and absorbs the strain from hefting a grinder or sander, Maxwell said. Tests found productivity gains of more than 30 percent, he said, and wearers showed their Macarena footwork to demonstrate the suits' flexibility.

"It turns workers away from being a weightlifter and into a craftsman," Maxwell said.

While Ekso Bionics' Harding sees exoskeletons on an evolutionary path toward ever-greater sophistication — much as large portable phones of the early 1990s morphed into today's smartphones — it may not be that easy to cut costs, simplify the technology and ensure widespread adoption.

"Even though there are processors and sensors, there's still a lot of physical matter that has to be machined and built," said Discern's Saffo.

The other limitation is battery life. Batteries can be made only so powerful before turning into a bomb, Saffo said. Boeing knows the risks in working with larger versions of the lithium-ion cells found in mobile phones: It's still trying to figure out the cause of electrical faults that grounded its 787 Dreamliner.