Understanding the numbers

Getting familiar with all the metrics that HRV Health produces can seem daunting at first. What is good? What is bad? What should you be looking for?

This article will answer those questions.

RMSSD is the measure of heart rate variability (HRV). The higher the number, the better. A good number is age and gender dependent, but generally if your HRV is below 20, it’s cause for concern, and you should be making lifestyle changes to improve your HRV. If you RMSSD is above 50, you are in good health, and you should be looking to maintain or improve that number.

More than anything, RMSSD is personal. If there is a decline in the RMSSD figure from one day to the next, think about what has caused the change.

Poor sleep, stressful incidents, too much alcohol, will all cause a decline in HRV. A steady decline may be a sign of a health issue, or if you’re an athlete, that you need to give more time to recovery. Overtraining syndrome (OTS) is an illness. If it’s not exercise, then consider visiting a doctor to find out what is causing the decline. Your heart it trying to tell you something, and you should listen.

Resting Heart Rate (RHR) is a measure of fitness. A figure of below 60 is good, above 80 is cause for concern. Age is a big factor, so you need to look at the RHR percentile which takes age and gender into account. That figure tells into which percentile of the population you fall. If your RHR percentile is 69.5, your RHR better than  69.5% of the population.

The percentile does the same for HRV. If your percentile is 85.3, you’re healthier than 85.3% of the population. [1]Short-term heart rate variability–influence of gender and age in healthy subjects

There are two metrics that measure stress: the Stress Index, and Stress. A stress index above 150 or stress above 10 are a sign that you are too stressed and that there is a high probability that your health is at risk. Take remedial action. In the short term, a massage or a weekend away. In the long term: yoga, pilates, exercise, or change your job.

Respiration is another measure of health. The lower the better, provided that you are not artificially holding your breath to get a low respiration rate. If the number is elevated, it can be a sign that the reading was not taken in a relaxed state. If it coincides with an elevated RHR, and you realise that you weren’t relaxed while taking the reading, you may need to take another reading. Or add a note in the comments field.

Under the Poincaré result tab, there are another group of metrics that are important. SD1 is the width of the Poincaré plot and SD2 is the length. You want the Poincaré plot to be long and thin. A lower SD1 is better, and so is a higher SD2. Athletes use the SD2 number as an indicator of recovery. If it’s lower than normal, you’re not fully recovered. When it’s at a peak, you’re ready for an intense work-out.

The ratio is SD2/SD1, and the higher the number is, the better. Below 2 is cause for concern.

Those are the most important metrics to consider. The others provide insights into the primary figures. For example, RMSSD is on a geometric scale. The score converts RMSSD to an arithmetic scale. Over time you will place more importance on the score, but until you are familiar with your score, RMSSD is the better measure.

The averages are calculated over the last 10 days, providing a 10 day moving average. The movements are measured in relation to the 10 day moving average.

Then you have the Days Streak. It’s important that you take your HRV daily. This gives you reliable metrics, and providing a far better understanding of what factors are affecting your health. After all, if there is something that is preventing you from taking a reading, it is something that is changing your plans, outside of your infuence, and that is almost always stressful. Try and get a good streak going, and keep it going. Our record is 1007 days.

Once you start getting used to your numbers, you will have a great grip on your health status, and you can start setting targets. Measuring HRV is serious, but remember to keep it fun. That’s how it works best for you.