Walking 'not enough to get fit'

From an article of the same title on BBCNews.com:

A team from Canada's University of Alberta compared a 10,000-step exercise programme with a more traditional fitness regime of moderate intensity. Researchers found improvements in fitness levels were significantly higher in the second group. They told an American College of Sports Medicine meeting that gentle exercise was not enough to get fit... "You've got to do more than light exercise and move towards the inclusion of regular moderate activity, and don't be shy to interject an occasional period of time at the vigorous level."