Fitbit Research Findings Show that Users Who Meet Physical Activity Recommendations Are Able to Improve Their Resting Heart Rate, Sleep, and More

Did you know that the famous 10K steps per day target wasn’t originally based in science? Manpo-kei, translated as “10,000-steps-meter,” was introduced by a Japanese pedometer manufacturer in 1965. As we know at Fitbit, a wide range of research has occurred since then, indeed suggesting that hitting this daily target can improve sleep duration and quality, have a positive impact on self-reported mental health, boost blood oxygen levels, and decrease resting heart rate. 

Research shows that it’s not only step count, but also intensity that matters. Since 2020, Fitbit has inspired Fitbit users to push up their physical activity levels with the introduction of personalized Active Zone Minutes (AZMs) minutes of high-intensity activity that are based on heart rate targets achieved for each minute spent on any workout that gets your heart pumping.

For this analysis, we investigated whether hitting the American Heart Association’s recommended physical activity target of 150 minutes per week of moderate intensity aerobic activity leads to measurable improvements in Fitbit users. We also took a look at approximately how long users should meet these physical activity targets to get the highest return on investment on these aspects of their health.

We analyzed 471 million AZMs and 106 billion steps of anonymous and consenting users who met the physical activity targets in February 2022, but not in January 2022, and assessed whether they saw corresponding improvements in their health compared with users who did not meet the targets in the same period. The results show positive health impacts across resting heart rate, HRV, sleep and stress management scores so long as at least one threshold is reached. Health benefits are even further pronounced when users achieve multiple recommendations.

Users who met both 10K steps per day and the 150 AZMs per week target saw improvements in multiple metrics compared to those who did not meet those thresholds. Specific improvements were as follows: 

• Heart rate variability improved by 20 percent (6.1 millisecond or ms. difference)
• Resting heart rate lowered by 8.1 percent (4 bpm difference)
• Stress management scores lowered by 7.3 percent (5.4 difference)¹ 

In addition, users that met or exceeded only the 10K steps per day recommendation still showed a 3.44 millisecond higher heart rate variability (higher is better), 3.05 beats per minute lower resting heart rate, and 3.97 improvement in their stress management score than comparable users. 

Users that met or exceeded only the 150 AZMs per week recommendation showed a 3.08 ms higher heart rate variability, 1.35 beats per minute lower resting heart rate, and 5.08 higher stress management score than comparable users. These findings suggest that meeting even one of the targets may still yield improvements in your health.

Next, we looked at how long the same user who initially does not meet the physical activity targets needs to be active to start reaping the health benefits:

• Reaching the 150 AZMs per week and 10K steps per day targets for as little as two weeks increased heart rate variability by 20 percent, decreased RHR by 4.3 percent, and increased sleep scores by 4.2 percent compared to remaining at below-target physical activity levels
• Users that managed to hit the physical activity targets for an additional two weeks (6 weeks total) also saw a 4.9 percent decrease in their resting heart rate²
• Importantly, these positive effects on health lasted for over 4 weeks even if activity later dropped!

Key recommendation: Shoot for 150 AZMs per week in addition to 10K steps per day for the biggest benefit. If that’s too much, aim for activity consistency balanced with some higher intensity workouts for measurable benefits. Use Fitbit’s Activity goals to set daily targets for steps and AZMs and remember to turn on those reminders to move! By enabling these features, Fitbit can help you set targets and achieve your health goals. 

¹ This analysis was not designed to directly compare the AZM and step count physical activity targets as these distinct workouts are subject to different variables that affect health, such as measurement error. So it is possible that the associations we found with health are attributable to some other unobserved characteristic of the workout.

² As these analyses were observational in nature, we were unable to control for all confounding variables, so it is possible that the associations we found with physical activity and health are attributable to other, unobserved characteristics in the groups. However, other studies, including prospective randomized controlled trials, have shown comparable changes in RHR and HRV over a similar time period.