HRV (Heart Rate Variability)

HRV: what is it?

Every wearable a client owns now reports HRV, which means coaches get asked about it whether they want to be or not. The measure itself is real: the interval between heartbeats is not perfectly regular, and the size of that variation tracks the balance between the sympathetic and parasympathetic branches of the autonomic nervous system. The trouble starts when a single morning number gets treated as a verdict on the day. Used as a trend, HRV is a useful conversation opener. Used as a daily instruction, it mostly produces anxious clients.

What the number is measuring

A heart at rest under strong parasympathetic ("rest and digest") influence beats with more variation between beats. Under sympathetic ("fight or flight") drive, whether from training stress, illness, alcohol, a bad night or a deadline, the rhythm becomes more metronomic and HRV falls. That is why the same reading can be pushed down by a hard leg session and by a stressful board meeting: the body does not label the source.

Most consumer devices report a version of RMSSD, often rescaled into a proprietary 0-100 score. That rescaling is why one client's 62 and another's 128 say nothing when compared directly.

Reading the trend, not the reading

HRV bounces around day to day even in a perfectly recovered person. The signal lives in the rolling average and in how far today sits from that client's own normal range, which is why most apps show a baseline band rather than a raw number. A single low day is noise. Several low days in a row, alongside worse sleep and heavier-feeling sessions, is information.

Measurement conditions matter more than clients expect. Compare like with like: same time of day, same position, ideally on waking before getting out of bed and before caffeine.

What HRV is not

HRV is not a fitness score, not a measure of how good the last session was, and not comparable between two clients. Age, genetics, resting heart rate, the device and the algorithm all shift the absolute value. A younger client will often show a much higher number than an older one with identical training and recovery habits.

It also cannot tell you the source of the stress. If a client's HRV drops after a week of travel, poor sleep and alcohol, the number gives you a reason to ask questions. It does not give you a reason to deload a training block that was going fine.

Using it without making clients anxious

The main failure mode of HRV coaching is that a client wakes up, sees a red score, and decides they are broken before their feet hit the floor. Some people train worse purely because of what their wearable told them. If a client is prone to that, the correct call is to stop showing them the daily number and look at the weekly trend together instead.

A simple rule works for most clients: the number never cancels a session on its own. It can prompt you to check in, and if the check-in confirms poor sleep, low motivation and heavy warm-up sets, then you adjust. Two signals agreeing is worth acting on; one number is not.

• Measure at the same time, in the same position, before caffeine.
• Look at a 7-day rolling average against the client's own baseline.
• Never compare one client's HRV to another's.
• Use it to start a conversation, not to end one.