We saw the electromagnetic shock portion in Captain America: The Winter Soldier, but what we didnt see was the fact that much like The Manchurian Candidate, Bucky was conditioned to respond to a special trigger that primed him to accept orders.
This trigger word doesnt really have a huge significance to Bucky, but it does seem to speak to the events of Captain America: Civil War, both in and outside of its cinematic universe.
Warning: Spoilers for Captain America: Civil War are in play.
Both men acknowledge that, technically, theyre 100 years old though in both of their cases, its more of an approximation, as Bucky was born in 1917, and Steve was born in 1918 according to Captain America: The Winter Soldier.