Developed by cardiologists from Johns Hopkins, the FIT Treadmill Score is based on basic treadmill performance measures taken from nearly 60,000 adults from Michigan between the ages of 18 and 96 years who completed a standard cardiac exercise stress test.
A stress test typically consists of a brisk walk on a treadmill, following a standardized procedure for increasing speed and elevation, while electrocardiographic monitoring detects any abnormal heart rhythms and other indicators that your heart is under stress from lack of oxygen during exercise.
To calculate a patient’s FIT Treadmill Score, doctors use a formula that factors in four key variables: age, gender, peak heart rate during intense exercise, and ability to tolerate physical exertion as measured by metabolic equivalents, or METs.
“METs are a measure of your heart’s workload based on the amount of oxygen it takes in and how much energy you use during exercise,” said David Langholz, MD, co-director, Spectrum Health Frederick Meijer Heart and Vascular Institute. “The higher the number, the more work your heart can do.”
While the link between how fit your heart is and your risk of death is nothing new, this formula is. For the first time, a simple equation, based solely on treadmill exercise performance, can gauge longer-term death risk.
Your score, the research team says, could yield valuable clues about your health and should be calculated for the millions of patients who undergo cardiac stress testing in the United States each year.
“This really is great news. How often do you get a chance to peer into your future and influence your own destiny?” Dr. Langholz asked. “People can see how they score now, and then take steps to improve their cardiovascular health and fitness level if they need to. A tool like this empowers people with the knowledge–and often the motivation–they need to actually change a predicted outcome. You can’t do that with a lot of diseases.”
How hard your heart works during your stress test, and your maximum heart rate as compared to what doctors might expect of someone your age and gender, are the most highly predictive of 10-year survival. Neither of these measures can be obtained from a home treadmill, Dr. Langholz noted.
Here’s how it works (caution: math ahead!)
FIT Treadmill Scores range from −200 to +200 and are stratified into three groups, each with a predictive 10-year survival rate. Those above 0 having lower mortality risk and those in the negative range facing highest risk of dying.
Patients 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. In other words, two of 100 people of the same age and gender with a score of 100 or higher would die over the next decade, compared with three out of 100 for those with a fitness score between 0 and 100.
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.
For example, a 45-year-old woman with a fitness score in the bottom fifth percentile is estimated to have a 38 percent risk of dying over the next decade, compared with 2 percent for a 45-year-old woman with a top fitness score.
- For men, the FIT Treadmill Score = PMHR (percentage of maximal heart rate) + (12 x MET) – (4 x Age)
- For women, the FIT Treadmill Score = PMHR + (12 x MET) – (4 x Age) + 43
If Score >= 100, 2% risk of death
If 100 > Score >= 0, 3% risk of death
If 0 > Score >= -100, 11% risk of death
If -100 > Score >= -200, 38% risk of death
A man with PMHR (%): percentage of maximal heart rate = 70.52228552, MET: metabolic equivalent of task = 6.64, Age (yrs): 48.45 has an 11% risk of death in 10 years.
Published along with the study is a chart depicting death risk by age, gender and fitness level, which can be printed on placards for use in physician’s offices to guide clinical advice.
Dr. Langholz said other stress test scoring systems measure shorter-term risk of death as well as risk of an impending cardiac event, such as a heart attack. These are used for patients with established heart disease or signs of cardiovascular trouble and also factor in other test results such as electrocardiograms.