How does an exoskeleton work?
Hydrolic pistons and servo motors act in conjunction with your own bodies movements (muscles) to 'enhance' your abilities (strength primarily at the moment).
I haven't seen any practical, real life examples (as in used by the military) but I have seen them in action (albeit in videos) in a crude form.
As you move your arm, the 'suit' detects this and moves with you, giving you extra strength.
So far as running goes, I'm not sure. I think the challenge there would be the same as with robots walking. I don't know if they've got them to 'enhance' running speeds or jumping. From memory, I can't recall seeing one work in such a fashion.