The path to better heart health might just run through your wrist.
Scientists at Northwestern University’s Feinberg School of Medicine have developed a new way to assess cardiovascular fitness using data from your smartwatch. All it takes is a little math.
“The metric we developed looks at how the heart responds to exercise, rather than exercise itself,” said Zhanlin Chen, the study’s lead author. “It’s a more meaningful metric because it gets at the core issue of capturing the heart’s capacity to adjust under stress as physical activity fluctuates throughout the day.”
Heart disease: The silent killer
Nearly half of American adults are estimated to have some form of heart disease. It remains the leading cause of death for men and women in the US, claiming a life every 33 seconds.
While simple medical tests can catch heart problems early and pave the way for life-saving interventions, studies show that many Americans are skipping their routine checkups and screenings.
The key to bridging this gap may lie in health tracking devices, which surveys suggest 44% of Americans own.
By harnessing the data your smartwatch is already collecting — like step counts and daily heart rate — researchers believe we can identify people at higher risk for heart disease and motivate them to take proactive steps toward better health.
A new way to measure heart health
For the study, scientists sifted through Fitbit data and electronic health records from nearly 7,000 U.S. adults involved in a research program supported by the National Institutes of Health.
Next, the team crunched some simple numbers, dividing each participant’s average daily resting heart rate by their daily step count. The result? A metric called average daily heart rate per step (DHRPS).
Researchers then compared this ratio with participants’ cardiovascular health data.
They found that people with a higher DHRPS — meaning their hearts have to work harder to keep up with daily activity — were 1.7 times more likely to have heart failure and 1.4 times more likely to have coronary atherosclerosis, or plaque buildup in your arteries.
Participants with a higher DHRPS were also twice as likely to develop type 2 diabetes and 1.6 times more likely to have high blood pressure compared to those with a lower DHRPS.
Researchers noted that the DHRPS metric proved to be a better predictor of heart disease risk than daily heart rate or step count alone. However, they found no link between DHRPS and the risk of stroke or heart attack.
“It’s a measure of inefficiency. It looks at how badly your heart is doing,” Chen told The New York Times.
“You’re just going to have to do a tiny bit of math,” he added.
What DHRPS ratio should you aim for?
For most adults, a normal resting heart rate falls between 60 and 100 beats per minute, according to the American Heart Association.
“If someone takes 10,000 steps a day and their heart rate was 147 beats per minute throughout the day, that could potentially signal their heart is working harder than it should,” Chen told Women’s Health.
In that case, their DHRPS would be 0.0147, which is considered high.
Now, compare that to someone else who also takes 10,000 steps but has an average heart rate of 80 beats per minute. That person would have a lower DHRPS of 0.008.
“That is in the range of what we would consider physiologically normal,” Chen said.
In short, the higher the ratio, the greater the cardiac risk.
Straightforward and user friendly
One of the biggest advantages of the DHRPS metric is its simplicity. The research team designed it with accessibility in mind, allowing people to calculate it on their own using quick math and data that’s already collected by their smartwatch.
Looking ahead, researchers plan to test whether tracking heart rate per step over minutes — rather than days — could be even more useful for doctors and patients.
With further refinement and validation from additional studies, Chen believes DHRPS could eventually be integrated into standard heart disease risk assessments used by clinicians. It could also make its way into smartwatch apps.
“Wearables are welcomed by the consumer and worn throughout the day, so they actually have minute-to-minute information about the heart function,” Chen said.
“That is a lot of information that can tell us about a lot of things, and there’s a need to further study how this detailed information correlates with patient outcomes,” he added.
