What they did in the first year is a good idea -- if you want to know how much something changes when you intervene in some way, measure it before and after the intervention, and compare. This is called a pre-post or before-after design. Here they just forgot to take a "pre" measurement on the second year people. There is no reason to believe that the second-year people would be starting from the same fitness level as the first-year people, and lots of reasons to believe that in fact the second-year people would be different: in its experimental first year, the program probably attracted a lot of fitness freaks, and then when it was so successful all the couch potatoes came out of the woodwork to sign up. Relative to where they started, the people in the second year may well have improved at least as much as those in the first year.