The trick, according the Maxwell, is having the assistance come at just the right time, in order to prevent the wearer from falling out of sync with the device, or "fighting" it. "It takes 75 milliseconds for the human body to go from thought to action," he said, referring to the time it takes for electrical impulses from the brain to initiate muscle movement in the body. As a result, the exoskeleton quickly becomes second-nature, ultimately reducing the metabolic "cost" of transport--the wearer's VO2max--by nine percent. In other words, soldiers don't have to consume as much oxygen to perform a given task, Maxwell says. Taking that edge off has associated benefits.