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, The Daily Item reports.

Lockheed Martin and Parker Hannifin are joining a handful of startups in finding uses and customers for bionic suits inspired by novelist Robert Heinlein’s 1959 “Starship Troopers” and Stan Lee’s Iron Man comic-book character.

The field may produce $400 million in annual revenue by 2020, according to technology consultant ABI Research.

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, managing director of foresight at investment advisory firm Discern in San Francisco.

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, to supply motive power. Computers and sensors help provide balance and guidance.

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 52,000-euro ($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.

“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, who is also a consulting associate professor at Stanford University’s engineering school.

The other limitation is battery life. Batteries can be made only so powerful before turning into a bomb, Saffo said.

Lockheed envisions a leap forward in battlefield mobility with its Human Universal Load Carrier — whose HULC acronym evokes images of Marvel Comics’ Incredible Hulk, a green, super- strong mutant and sometime-ally of Iron Man. HULC is intended to let a soldier lug a 200-pound pack with minimal effort over a 20-kilometer (12.4-mile) hike, Maxwell said.