What this means is that they used statistical methods to effectively "equalize" everyone's weight, blood pressure, cholesterol, and so on. But this is absurd when you think about it. Why do we think running is good for health? In part because it plays a role in reducing weight, blood pressure, cholesterol, and so on (...)
They're effectively saying, "If we ignore the known health benefits of greater amounts of aerobic exercise, then greater amounts of aerobic exercise don't have any health benefits."