Treadmill performance predicts risk of death, researchers say

Cardiologists at Johns Hopkins University School of Medicine have devised a formula that estimates an individual’s risk of dying based on their ability to exercise on a treadmill.

In a new study published in the journal Mayo Clinic Proceedings, researchers analyzed data from 58,000 heart stress tests and created an algorithm to gauge mortality risk over a decade based solely on treadmill exercise performance. While exercise-based risk scoring systems for short-term mortality exist, they are only used for patients with established heart disease or overt signs of cardiovascular trouble. This new algorithm, the FIT Treadmill Score, is applicable to anyone.

“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,” lead investigator Dr. Haitham Ahmed, a cardiology fellow at the Johns Hopkins University School of Medicine, said in a news release.

The FIT Treadmill Score factors in age, gender, peak heart rate reached during intense exercise and the ability to tolerate physical exertion. The last factor is measured by metabolic equivalents (METs), a gauge of how much energy the body expends during exercise. More vigorous activity requires higher energy output (higher METs), better exercise tolerance and higher fitness level, according to the news release. For example, slow walking equals two METs, but running is eight METs.

One benefit of the test is that it’s easy to calculate and costs nothing beyond the cost of the treadmill test itself, researchers said.

“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, senior study author Dr. Michael Blaha,  director of clinical research at the Johns Hopkins Ciccarone Center for the Prevention of Heart Disease, said in the news release.

According to researchers, the new data shows that varying degrees of fitness among those with “normal” exercise stress test results reveal telling clues about cardiac and respiratory fitness— and therefore overall death risk over time.

Researchers analyzed data on 58,020 people, ages 18 to 96, who underwent standard exercise stress tests between 1991 and 2009 in Detroit, Michigan. They then tracked how many participants within each fitness level died from any cause over the next decade.

Among people of the same age and gender, fitness level as measured by METs and peak heart rate reached during exercise were the greatest indicators of death risk. Additionally, fitness level was the single most powerful predictor of death and survival, even after accounting for important variables such as diabetes and family history of premature death.

An example of their analysis found that 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 to a 2 percent risk for a 45-year-old woman with a top fitness score.

“We hope that illustrating risk that way could become a catalyst for patients to increase exercise and improve cardiovascular fitness,” Blaha said.