How You Perform on a Treadmill Could Predict Mortality
A team of cardiologists at Johns Hopkins University has developed a formula to estimate an individual’s risk of dying over a decade based on their ability to exercise on a treadmill at increasing incline and speed. Their findings were published in the Mayo Clinic Proceedings in 2015.
While there are already several exercise-based risk scoring formulas in use, they are generally designed to measure short-term risk of death among patients who already exhibit symptoms of heart disease and combine exercise-based scoring with results from additional tests like electrocardiograms (EKGs).
The new formula, named the FIT Treadmill Score, is unique in that it analyses long-term risk of dying based exclusively on an individual’s performance on the treadmill. Researchers say this score could produce valuable information about an individual’s health, and they recommend that it be calculated for patients who undergo cardiac stress testing.
“The notion that being in good physical shape portends lower death risk is by no means new, but we wanted to quantify that risk precisely by age, gender and fitness level, and do so with an elegantly simple equation that requires no additional fancy testing beyond the standard stress test,” said lead investigator Haitham Ahmed, cardiology fellow at the Johns Hopkins University School of Medicine in a press release.
The FIT Treadmill Score takes into account factors like gender and age, as well as an individual’s ability to tolerate physical exertion. This last factor is measured by metabolic equivalents, or METs, which calculate how much energy the body expends during physical activity.
For the study, researchers analyzed the standard stress tests of 58,020 adults between the ages of 18 and 96, performed in Detroit from 1991 to 2009. They then tracked how many patients from each fitness level died from any cause over the next decade. The study found that fitness level (measured by peak heart rate during exercise and METs) was the greatest indicator of death risk among people of the same age and gender.
FIT Scores during the study ranged from negative 200 to positive 200. Researchers found that individuals who scored between 100 and 200 had a 2 percent risk of dying within the next decade, and those between 0 and 100 had a 3 percent risk of death. On the negative side, individuals scoring between 0 and negative 100 had an 11 percent risk of dying within the next decade, while those between negative 100 and negative 200 had a 38 percent chance of death.
The results of the study showed that “fitness level was the single most powerful predictor of death and survival.” This remained true even after researchers adjusted for influential factors like diabetes and family history of early death, underscoring the importance of heart and lung fitness.
“The FIT Treadmill Score is easy to calculate and costs nothing beyond the cost of the treadmill test itself,” said senior study author Michael Blaha, director of clinical research at the Johns Hopkins Ciccarone Center for the Prevention of Heart Disease. “We hope the score will become a mainstay in cardiologists and primary clinicians’ offices as a meaningful way to illustrate risk among those who undergo cardiac stress testing and propel people with poor results to become more physically active.”
Currently used exercise-based stress tests, which measure heart and lung performance while a person exercises on a treadmill, stop when a person reaches exhaustion or experiences dizziness, heart rhythm abnormalities or chest pain. Those who present abnormal EKGs or symptoms related to abnormal heart strain are referred for further testing, while those who present normal EKG readings and present no symptoms are not generally subjected for further testing.
According to the researchers, however, there is a lot that can be learned about cardiac and respiratory fitness from new data showing different degrees of fitness among patients with a “normal” stress test.
“Stress test results are currently interpreted as ‘either/or’ but we know that heart disease is a spectrum disorder,” said Ahmed. “We believe that our FIT score reflects the complex nature of cardiovascular health and can offer important insights to both clinicians and patients.”