It was never really explained to me how the Spartans of the Halo series were so strong and resilient to attack. Well, I’m still not too sure on the resilience front but if they are humans inside some suits, it might not be as science fiction as some may think.
Introducing the Sarcos XOS exoskeleton, a suit that has a working prototype (see here: http://gizmodo.com/gadgets/humanoids/sarcoss-exoskeleton-is-more-amazing-than-we-thought-326128.php). A normal person can jump into the suit and as they move the exoskeleton will move with them, except for the fact that the endurance of metal is far above a human’s. That and the suit is far stronger than a human. Planned for use in the military, the XOS could be the next step in one on one combat. All that is required now for the “combat evolved” that the original halo spoke of is some ability to take a large amount of bullets without getting any bigger or cumbersome (check out the video, I personally want to see what it can do to a punching bag with full force).
