The U.S. military has been attempting to design futuristic, performance-enhancing exoskeletons for combat soldiers since the late 1990s, but the technology often interferes with the way humans move.

"The human-exoskeleton interface raises a number of potential issues. Most exoskeletons contain rigid elements that can restrict natural movement," according to a recent request for information solicitation posted on www.sibr.gov, a government website for the Small Business Innovation Research (SBIR) program, which is designed to encourage small business to engage in federal research and development.

"The objective of this effort is to demonstrate an interface that can safely join an exoskeleton (which is potentially rigid and/or heavy) to a human being (which is fleshy and load-limited) while simultaneously optimizing the mobility of and minimizing the injury to a dismounted soldier," it states.