man walking with smartwatch
man walking with smartwatch
That fitness tracker on your wrist might be capable of much more than counting steps or monitoring your sleep. A new study suggests that a simple mathematical relationship between your heart rate and daily steps could offer a more meaningful glimpse into your cardiovascular health than conventional metrics—potentially flagging heart problems before they become serious.
Researchers at Northwestern University have developed what they call “daily heart rate per step” (DHRPS), a calculation that divides a person’s average daily heart rate by their total daily steps. This novel approach, presented at the American College of Cardiology’s Annual Scientific Session this March, could transform how we use the data already being collected by millions of smartwatches worldwide.
“The metric we developed looks at how the heart responds to exercise, rather than exercise itself,” explained Zhanlin Chen, a medical student at Northwestern University Feinberg School of Medicine in Chicago and 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. Our metric is a first attempt at capturing that with a wearable device.”
The concept addresses a fundamental limitation in conventional fitness tracking. While step counts can indicate activity levels, they reveal little about how efficiently your cardiovascular system handles that activity. Similarly, resting heart rate alone doesn’t capture your heart’s responsiveness during varying levels of exertion.
Data From Thousands Reveals Clear Patterns
To validate their approach, researchers analyzed an impressive data set from the National Institutes of Health’s All of Us research program, which included Fitbit data and electronic health records from nearly 7,000 U.S. adults. The scale is striking: 5.8 million person-days of monitoring and a staggering 51 billion total steps.
What they found suggests the DHRPS calculation might indeed provide valuable health insights. People with elevated DHRPS scores—those in the top 25th percentile—faced substantially higher odds of having several cardiovascular conditions compared to those with lower scores. The numbers tell a concerning story: approximately twice the likelihood of Type 2 diabetes, 1.7 times higher odds of heart failure, 1.6 times greater chance of having hypertension, and 1.4 times increased risk of coronary atherosclerosis.
Notably, the study found DHRPS was more strongly associated with these cardiovascular diagnoses than either daily heart rate or step count when considered individually. This pattern held true in a smaller subset of 21 participants who underwent treadmill stress testing, where DHRPS showed a stronger correlation with maximum metabolic equivalents (METs) achieved during the test.
Heart disease remains America’s leading killer, claiming more lives each year than any other condition. While screening tests exist, many people don’t undergo recommended evaluations. The potential for a passive, continuous monitoring system built into devices millions already wear daily could represent a significant public health opportunity.
From Research to Real-World Application
The concept’s simplicity is perhaps its greatest strength. As Chen points out, individuals could calculate this metric themselves using data their smartwatches already collect, or the calculation could be integrated into fitness 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 noted. “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.”
However, the researchers emphasize this study represents only initial validation. Its cross-sectional design means they couldn’t determine when the Fitbit measurements were taken relative to when cardiovascular conditions were diagnosed—an important limitation. Interestingly, the study found no relationship between DHRPS and the risk of stroke or heart attack, suggesting the metric may be better at identifying certain cardiovascular issues than others.
Looking ahead, the team hopes to conduct more prospective studies with higher temporal resolution, tracking DHRPS at minute-by-minute intervals rather than using data aggregated across days. Such refinements could potentially strengthen the metric’s predictive value.
The Future of Wearable Health Monitoring
This research comes at a time when wearable health technology is evolving rapidly. Major smartwatch manufacturers continue adding advanced sensors to their devices, from ECG capability to blood oxygen monitoring. The DHRPS approach is distinctive in that it doesn’t require new sensors—just a smarter way of analyzing data already being collected.
If further validated, Chen suggests DHRPS or similar metrics could eventually be incorporated into standard heart disease risk assessments used by clinicians. This integration would represent a significant step toward bridging the gap between consumer fitness tracking and clinical health monitoring.
For the millions of Americans who wear fitness trackers daily, this research suggests their devices might already be capturing valuable health insights hiding in plain sight—insights that could one day provide early warning of cardiovascular issues before traditional symptoms appear.
The question now is whether this mathematical relationship between heart rate and steps will prove robust enough across larger populations and longer timeframes to become a standard tool in preventive cardiology. If so, that fitness tracker on your wrist might deserve more credit than simply counting your daily steps—it could be quietly calculating a number that provides meaningful insight into how well your heart is performing when you need it most.
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