Calculating your own score.So how exactly is it done? The test consists of three-minute segments that increase in speed and incline. In the study, people exercised until they were fatigued, felt chest discomfort, or until a clinician saw something suggesting lack of blood flow to the heart, says Ahmed. Below is an example of the stages of incline and speed from the Bruce Protocol: Stage 1 1.7 mph/10% grade/5 METs Stage 2 2.5 mph/12% grade/7 METs Stage 3 3.4 mph/14% grade/10 METs Stage 4 4.2 mph/16% grade/13 METs Stage 5 5.0 mph/18% grade/15 METs Stage 6 5.5 mph/20% grade/18 METs Stage 7 5.5 mph/22% grade/20 METsIn addition to accounting for age and sex, the formula used in the study factored in how well you tolerate exercise measured in metabolic equivalents or METs, says Ahmed. This tells you how much energy youre expending while working out. (More vigorous exercise means higher METs.) The longer you can stay on, the more METs you accrue, he says, noting that the median MET score was 10. More than 10 METs was associated with a higher fitness level and good survival rate.Then, researchers used the following formula:(12 x METs) + (% of maximum predicted heart rate) (4 x age) + 43 if female.*Maximum predicted heart rate is calculated as 220 age. Heart rate achieved during exercise should be divided by maximum predicted. For example, if youre 20 years old, your maximum predicted heart rate is 200 (220 20). If you achieve 180, you achieved 90 percent of maximum.You want a positive score. If you have at least zero, your survival rate is 97 percent in the next decade, says Ahmed. In the study, scores ranged from negative 200 to positive 200. People who scored 100 or higher had a 2 percent risk of dying over the next 10 years, while those with scores between 0 and 100 faced a 3 percent death risk over the next decade, researchers noted. People with scores between negative 100 and 0 had an 11 percent risk of dying in the next 10 years, while those with scores lower than negative 100 had a 38 percent risk of dying. Why fitness matters.Of all the parameters measured, METs and fitness levels were the strongest predictor of whether a person would live or die, even after accounting for family history, disease, and health habits, says Ahmed. After fitness, age, and gender, almost nothing else mattered or improved survival. How come? The answer lies in what we know to be true: the vast power of exercise, he says. We understand a lot about fitness. And while there is still a lot to learn, we know that usually, those who exercise more often have lower obesity rates, lower blood pressure, lower risk of diabetes, a reduced risk of blood clotting, reduced inflammation, and lower levels of bad cholesterol.The good news: In a pricey world of medical testing, medications, and gym memberships, cardio is a free way to add years to your life. We have come into an age where medical testing is expensive, says Ahmed. This is a score that costs nothingit is virtually free besides the treadmill.And if youre not happy with your fitness levels, theres room to grow: Today, we think of standard stress tests in terms of pass and fail, but thats an outdated way to think of risk.