Double points are given if more than two departments are working out together.
Dr Laura Joyce, one of the organisers, said last year's inaugural challenge was a big success, especially in getting people to better know one another.
"We work in really big departments and because you work shifts, you don't actually see everyone that often, and it's quite easy to forget, or not know, the names of some of the staff because you don't see them frequently," Dr Joyce said.
"Say someone comes in from a car crash, there'll be 10 or 15 people working as a team, and knowing everyone's names is really helpful. This challenge has been great to get people to sit in the tearoom and talk to each other."
The challenge started on Monday and runs until April 18.
Although all 600 members of the two departments have been signed up to the challenge, taking part is optional.
Dr Joyce said there was some "healthy peer pressure" for people to get involved.
Families and children are also encouraged, and around 100 people turned out to the first of a series of 5km runs at Hagley park in central Christchurch last night.
The winning team secured "bragging rights", Dr Joyce said, but also a trophy which sits in pride of place in the ED.
Dr Jan Bone, another of the main organisers, said the challenge has already shown its benefits in the workplace.
"It's amazing when you provide a platform for people to interact with each other, get fitter and healthier and make it fun - the spin offs are wonderful. The buzz at work has really improved people's sense of belonging and contributing to the department."