NEW YORK, April 2: Many people use smartwatches to track their cardiovascular health, often by counting daily steps or monitoring their average heart rate. Researchers, however, are now proposing an improved metric that combines both of these measurements through simple math: divide your average daily resting heart rate by the average number of steps you take each day.

The result — the daily heart rate per step (DHRPS) — provides insight into the efficiency of your heart's function, according to a study from the Feinberg School of Medicine at Northwestern University, published today in the Journal of the American Heart Association.

The study revealed that individuals with a less efficient heart, as indicated by this metric, were at a higher risk for various diseases, including Type II diabetes, hypertension, heart failure, stroke, coronary atherosclerosis, and myocardial infarction.

“It reflects inefficiency,” said Zhanlin Chen, a third-year medical student at Feinberg School of Medicine and lead author of the study, which also involved several faculty physicians from the university. “It shows how well your heart is performing,” he added. “All it takes is a little bit of math.”

Some experts see value in the DHRPS as a metric. Dr. Peter Aziz, a pediatric cardiologist at the Cleveland Clinic, believes it offers more meaningful insight than daily steps or average heart rate alone. “What’s probably more important for cardiovascular fitness is how your heart handles the work it’s given,” he said. “This seems like a reasonable way to measure that.”

Although the metric doesn’t account for heart rate during exercise, Dr. Aziz noted that it still provides a general sense of heart efficiency, which, importantly, has been shown to correlate with disease risk.

The large sample size of the study adds credibility to its findings, according to Dr. Aziz. Researchers analyzed Fitbit data from nearly 7,000 smartwatch users, comparing it to their electronic medical records.

Chen explained that the new metric can be easily understood by comparing two hypothetical individuals. Both take 10,000 steps a day, but one has an average resting heart rate of 80 — a healthy range — while the other’s is 120. The first person’s DHRPS would be 0.008, while the second would be 0.012. A higher ratio indicates greater potential cardiac risk.

The study divided the 6,947 participants into three groups based on their DHRPS ratios, with those in the highest group showing a stronger association with disease. The DHRPS metric proved more effective in predicting disease risk than step counts or heart rates alone.

“We created this metric to be low-cost and based on data people already collect,” Chen said. “It’s something anyone can easily calculate to take charge of their own health.”