Resting heart rate
How hard does your heart have to work—and how fast does it have to pump—to get oxygen-rich blood throughout your body? A lower number suggests your cardiovascular system is more efficient at doing this. Thus, a highly trained athlete can have a resting heart rate in the 40s, says Whiteson.
And while the research is still emerging on what one's resting heart rate predicts about heart disease risk, a picture is beginning to take shape. "There is certain evidence to support [the idea that] a higher resting heart rate is associated with heart disease," especially ischemic heart disease, he says, which involves reduced blood flow (and oxygen) getting to heart arteries and the heart muscle. This effect seems to be more pronounced in women than in men, but a study in the Journal of Epidemiology and Community Health suggested that in women up to the age of 70, every 10-beats-per-minute increase in resting heart rate boosted the risk of dying from ischemic heart disease by 18 percent. In men, the risk was increased by 10 percent for every extra 10 beats per minute, and age didn't have an impact. The study also found that women who got high levels of physical activity were able to reduce their risk of death considerably, compared with those who did little or no activity. The same effect was not found in men, but the researchers suggest the results may have been skewed because men tend to overestimate how much exercise they get.