In a novel new study, researchers have shown that aerobic fitness is directly related to lifespan. Researchers studied a database of 122,007 middle-aged or older men and women who underwent treadmill stress tests. Then they examined death records in the decade after the tests. The results show that people with high aerobic endurance live longer and are 80 percent less likely to die prematurely than people with the lowest endurance. And the research suggests that there is no upper limit to fitness, meaning you cannot become too fit. Instead the more fit you become, the longer you live. This is still a correlation study and does not prove causation. But the novelty of this study is that it used quantitative data from exercise tests, determined aerobic fitness and then looked at longevity, rather than using surveys that depend on people’s recollection of their exercise routine. Also of note is that the data show that being out of shape, with low endurance on treadmill tests, has the same effect on premature death as does smoking. So focus on endurance and don’t stop pushing for further improvement, because every bit counts.