Jason Kerestes co developed the AirLegs exoskeleton with the support from DARPA. The machine is pretty small and it is worn on the back. It also gives the wearer superhuman abilities - it decreases the metabolic cost of walking and running by about 10%.
"This device was tested at the Army Research Laboratories in September 2013 and demonstrated a 10% reduction in metabolic cost (compared to no device) for users running at high speeds. It is the only device known to the US Army to oficially augment the human running gait cycle."

Check it out below: