A University of Texas report looked into VO2 max, lactate threshold, and running economy of runners as they aged. The first two measures seem to decline inevitably with aging; running economy stays about the same. VO2 max and lactate threshold might slide downhill as we age simply because we can't train as hard. Or there could be other reasons. Whatever the case, many masters runners hold onto a high degree of fitness as they age. Considering I’m only four years away from “masters” status, this is good news. I know many men and women of “masters” status who continue to improve, which is so inspiring to me. I would assume that a big part of their continued success comes from their willingness to do the work, among myriad other factors.