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Heart rate, steps & VO2 Max: What smartwatch data reveals

A new study published in the Journal of Medical Internet Research (JMIR) has shed light on how smartwatch data can help monitor cardiorespiratory fitness (CRF). By examining heart rate and step counts, this study uncovers a significant correlation between smartwatch-derived metrics and peak oxygen uptake (VO₂ Max).

This cohort study involved a total of 662 participants. All of them used a Samsung Galaxy Watch Active or Active 2 devices. During the observation period which lasted 3 years, researchers collected data on heart rate and step counts. Participants also performed CPET to measure VO2 peak, a key indicator of cardiorespiratory fitness.

Key findings

The study reported mean VO2 peak values of 34.4 mL/kg/min for men and 27.6 mL/kg/min for women. As you’d expect, those who engaged in higher levels of physical activity demonstrated VO2 peak values up to 5 mL/kg/min higher than their less active counterparts.

The study found that men generally had higher VO2 peak values compared to women. However, both genders showed significant improvements in VO2 peak with increased physical activity.

Here are some other findings:

Heart rate correlations: The study found a significant inverse correlation between resting heart rate (RHR) and VO₂ peak. A 0.27 ml/kg/min decrease was observed in VO₂ peak for every one-beat-per-minute increase in RHR. In practical terms, a participant with a RHR of 60 bpm would be expected to have a VO₂ peak that is 2.7 ml/kg/min higher than someone with a RHR of 70 bpm.

Impact of physical activity: Increased daily step counts also link to higher VO2 levels. An additional 1,000 steps per day is associated with a 1.3 mL/kg/min increase in peak VO2. This translates to a participant with 10,000 daily steps having a VO₂ peak that is 2.3 ml/kg/min higher than those with 5,000 daily steps.

The study showed that participants in the highest quartile of daily step counts had significantly higher VO2 peaks compared to those in the lowest quartile. This suggests that even modest increases in physical activity can lead to meaningful improvements in CRF.

Ventilatory efficiency and blood pressure: Measures of ventilatory efficiency and blood pressure responses to exercise showed an association with non-active heart rate, further highlighting the utility of heart rate monitoring. Lower non-active heart rates correlated with better ventilatory efficiency and more favourable blood pressure responses during exercise.

Heart rate variability: The study also observed that greater heart rate variability (HRV) during non-active periods correlated with higher VO2 peak values. HRV, a measure of the variation in time between heartbeats, often serves as an indicator of autonomic nervous system function.


The study’s findings highlight the potential of smartwatches to democratize the monitoring of cardiorespiratory fitness. By providing continuous, real-time insights into heart rate and physical activity, smartwatches can offer a practical approach to tracking and improving cardiovascular health.

Essential readingTop fitness trackers and health gadgets

For example, users can set daily step goals to gradually increase their physical activity levels, thereby improving their VO2 peak over time. Additionally, tracking resting heart rate and HRV can provide further valuable feedback on their progress.

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Ivan Jovin

Ivan has been a tech journalist for over 7 years now, covering all kinds of technology issues. He is the guy who gets to dive deep into the latest wearable tech news.

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