07/24/2026
đź’™ Understanding HRV, RMSSD, SDNN, and Why RingConn Doesn't Currently Sync HRV to Apple Health
Lately, we've seen a lot of discussion around HRV, RMSSD, SDNN, and Apple Health.
First, thank you to everyone who's shared feedback, exchanged ideas, and joined the conversation. We really appreciate it.
Those discussions have helped us better understand which topics could use a bit more explanation, so we wanted to take a moment to walk through them in a clear and straightforward way.
đź«€ What is HRV?
HRV stands for Heart Rate Variability. It isn't your heart rate — it's the variation in time between one heartbeat and the next.
By looking at these small changes, HRV can provide valuable insights into your recovery, stress levels, and overall well-being.
Many wearable devices measure HRV, but they don't all calculate it the same way. Two of the most commonly used HRV metrics are RMSSD and SDNN.
Both measure HRV, but they focus on different aspects of it. That's why they aren't directly comparable or interchangeable.
đź“Š What's the difference between RMSSD and SDNN?
A simple way to think about it:
• RMSSD focuses on short-term changes between consecutive heartbeats, making it especially useful for tracking recovery, sleep, and stress.
• SDNN reflects overall heart rate variability across a longer period, making it better suited for observing longer-term patterns.
Here's an easy example.
Imagine a student receives four test scores:
80, 90, 80, 90
RMSSD asks:
"How much did each score change compared with the previous one?"
SDNN asks:
"How much do all four scores vary from the average?"
They're looking at the same set of numbers—but from different perspectives. So it's completely normal for them to produce different results.
To help visualize this, we've created a simple simulation using NN interval data.
(The illustration uses simulated data to demonstrate the calculation and trend differences between RMSSD and SDNN. It does not represent real user data or product testing.)
đź’ˇ Why does RingConn use RMSSD?
There isn't one single way to measure HRV. Different metrics are designed for different purposes.
RingConn uses RMSSD because it's well suited for continuous health monitoring with wearable devices and is especially responsive to changes in recovery.
Combined with sleep, stress, and activity data, RMSSD helps users better understand how their body is recovering from day to day and how those patterns change over time, providing useful insights to support rest, exercise, and healthy lifestyle decisions.
For everyday health tracking, we believe long-term trends are more meaningful than any single number. Understanding how your body changes over time is what helps turn health data into something truly useful.
🍎 Why doesn't RingConn currently sync HRV to Apple Health?
This has been one of the biggest topics in recent discussions, and we'd like to share the thinking behind our current approach.
1️. RingConn and Apple Health use different HRV metrics.
Apple Health currently displays HRV using SDNN, while RingConn uses RMSSD.
Although both are HRV metrics, they're calculated differently and reflect different physiological perspectives. Because of that, they shouldn't be treated as the same measurement or compared directly.
2️. We want to keep health data accurate and consistent.
Health data is more than a collection of numbers—it should accurately represent what it's intended to measure.
If RMSSD were written into Apple's SDNN field, two different metrics would end up being mixed together. That could make data appear inconsistent across devices and make health trends harder to interpret.
Rather than forcing compatibility, we'd rather preserve the meaning and integrity of each metric.
3️. It also helps ensure more reliable health insights.
Many health apps read HRV data from Apple Health for further analysis.
If different HRV metrics are mixed together, those apps may interpret them as the same type of measurement, which could affect recovery insights, trend analysis, and other health metrics.
To help avoid confusion and keep health insights as reliable as possible, we believe it's important to keep these measurements separate.
For that reason, RingConn does not currently sync RMSSD directly to Apple Health.
This isn't because RingConn can't measure HRV. It's simply our way of making sure the health data you see remains accurate, consistent, and meaningful.
đź’™ We'd Love to Keep the Conversation Going
Health is a long-term process, and we're learning alongside our community every day.
This post may not answer every question, and there may still be areas we can explain more clearly.
If you have thoughts, questions, or feedback about HRV, RMSSD, SDNN, Apple Health, or any other health metrics, we'd love to hear from you.
Leave us a comment below. We read every piece of feedback, and your discussions help us improve not only our products, but also how we communicate and share health knowledge with the community.
If there's anything you'd like us to explain in more detail—or if you think there's a better way we could present this information—please let us know.
Thank you for being part of the RingConn community. We look forward to continuing the conversation and making health insights easier to understand, together. đź’™
