What your HRV says about today’s plan

In short

• Two healthy people of the same age can have an HRV that differs by a factor of two or three, without one being fitter than the other.
• So only compare your HRV with your own readings, from the same device and in the same measure.
• If your HRV this morning is clearly below your usual swing, there is no hard session in your plan today.
• A high HRV does not make your day harder.

1.What HRV is

HRV stands for heart rate variability: the small differences in time between two consecutive heartbeats. At a heart rate of 60, your heart does not beat exactly once a second. One beat comes after 0.95 seconds, the next after 1.08. That variation is not a measuring error. It shows that your heart can adjust quickly.

Those adjustments come from your autonomic nervous system. When you are rested and relaxed, the braking side has the upper hand and the variation is large. When your body is under pressure, from a hard session, poor sleep, stress, alcohol or an infection on its way, the rhythm becomes tighter and your HRV drops.

So HRV is not a heart rate. A low resting heart rate and a high HRV often go together, but they measure different things. Heart rate counts the beats. HRV measures how freely the gap between them moves.

2.Why there is no good HRV for everyone

Two healthy people of the same age can have an HRV that differs by a factor of two or three, without one being fitter than the other. Genes, age and build decide much of the level. A table with a good value per age therefore says little about you.

On top of that, there are two common measures that are both called HRV. rMSSD looks at the difference between each pair of consecutive beats and mostly follows the braking side of your nervous system. It is the measure most watches, rings and measuring apps show. SDNN looks at the spread of all beats across the whole reading, and it also picks up your breathing and everything your heart rate did in those minutes. Apple Health stores HRV as SDNN.

For the same person the two numbers do not sit at the same level, and two devices using the same measure do not read exactly alike either. So only compare your HRV with your own readings, from the same device and in the same measure.

3.How Trimetra builds your own baseline

Trimetra compares your HRV with yourself. Your readings from the past weeks form a baseline: the range your HRV moves in when everything is normal for you. How wide that range is differs from person to person. For one person HRV jumps around from day to day, for another it barely moves. A dip only counts when it is larger than your usual swing.

The last few days count separately. That way a dip does not drag its own comparison down with it, and you see the difference between one low morning and a week that keeps sitting lower.

Your baseline comes from one measure and one device. If you have a usable rMSSD series, Trimetra works with that, and only without rMSSD with SDNN. If two devices write HRV, the device that measures most often counts. A day without a reading from that device is then a day without a reading. Two scales are never mixed.

In the first weeks your baseline is still thin. A deviation then has to be larger before your plan responds to it, and every week of readings makes it sharper.

4.What a low HRV does to today’s plan

If your HRV this morning is clearly below your usual swing, there is no hard session in your plan today. An interval session or tempo run becomes an easy one. If the dip is deep, it becomes a recovery day.

If your HRV stays lower than normal for a week, even without one big outlier, that weighs more than a single morning. Quality then stays out for the next few days, and with a clear decline those days take on the character of recovery.

A high HRV does not make your day harder. It is a brake, not an accelerator: a good morning is no reason to do more than your plan already asked.

Your HRV never stands alone. Your resting heart rate, your sleep and any complaints count too, and when a day is adjusted the reason comes with it, so you can see what the change rests on.

5.How to measure reliably

Measure at the same moment every day. The best moment is right after waking up, before you get up, drink coffee or pick up your phone. A watch or ring that measures your night works too. Just do not mix the two, because a night value and a morning reading do not sit at the same level.

Take the same position every time. Lying down or sitting makes little difference, as long as it is the same every day. Standing gives a lower HRV. Breathe normally and calmly, because deliberately slow or deep breathing pushes your HRV up.

A reading of one to five minutes is enough. Shorter gets noisier, and longer adds little.

A chest strap is more accurate than a wrist sensor. It picks up the electrical beat of your heart, while a wrist sensor follows the blood flow under your skin and is sensitive to movement and a loose strap. At night, when you lie still, a watch or ring does a fair job, as long as you keep wearing the same device.

If you switch devices, your HRV makes a jump that has nothing to do with your body. A new device therefore starts with a new baseline, and that needs a few weeks again.

6.When your HRV is low and you feel fine

That happens a lot, and there is usually an ordinary explanation. Alcohol lowers your night HRV, sometimes a lot, even after one or two drinks. A late, heavy meal, a warm bedroom, travel or a short night do the same.

For women, HRV moves with the menstrual cycle. In the second half it is often a little lower and the resting heart rate a little higher. You can read more about it in the article on a higher heart rate before your period.

Sometimes your HRV sees a cold coming before you feel it. A low HRV together with a higher resting heart rate, on a morning when you feel not quite right, is a good reason to keep things easy.

Your plan is a suggestion. If you feel good and you know where the dip comes from, one low morning is no reason to worry. Today your plan holds back a little, and tomorrow the comparison starts again.

Frequently asked questions

In the app

Further reading

Trimetra sets your HRV against your own weeks, from one device and one measure, and only holds your plan back when a dip is larger than your usual swing.