What heart rate variability tells us about stress

Heart rate variability, or HRV, is one of the core signals behind Everis. It's also one of the most misunderstood. Here's what it is, what the research says, and how we use it responsibly.

What HRV is

Your heart doesn't beat like a metronome. The time between beats varies slightly from one beat to the next. HRV measures that variation.

That variation is shaped by the autonomic nervous system, the part of the nervous system that runs automatically. Its two branches pull in different directions: the sympathetic branch prepares the body for action, and the parasympathetic branch supports rest and recovery. In general, higher HRV reflects stronger parasympathetic activity and a body that is coping and recovering well. Lower HRV can reflect stress, fatigue, illness or poor recovery.

What the research says about stress

Kim and colleagues (2018) reviewed and meta-analysed the literature on stress and HRV and found that HRV changes in response to stress, with measures of parasympathetic activity typically decreasing under stress. Their conclusion was that HRV is a useful objective indicator of psychological stress.

De Looff and colleagues (2018) systematically reviewed studies of autonomic activity in job stress and burnout. They found associations between work stress and lower parasympathetic activity, while noting that the evidence was mixed across studies and measurement methods. That nuance matters.

Why we read HRV carefully

HRV is sensitive, which makes it useful, but it responds to many things besides work stress: exercise, alcohol, illness, poor sleep, travel and more. A single low reading means very little on its own.

So we:

• Use personal baselines. HRV varies widely between people, so each person is compared with their own normal.
• Look at trends. A sustained drift over weeks matters. A dip after a hard weekend doesn't.
• Combine signals. HRV is read alongside resting heart rate, sleep and validated survey scores. When several move together, the picture is clearer.
• Put a physiologist in the loop. Exercise physiologists add context the data can't see, and decide whether a flag needs action.

Why physiologists matter here

Endurance coaches have used HRV for years to manage training load and recovery. Our physiologists read it every day for athletes, and know its strengths and its pitfalls. That experience is what turns a noisy signal into a useful one.

What HRV is not

HRV is not a diagnosis. A low HRV trend doesn't mean someone has a medical condition. It's an early indicator that recovery may not be keeping up with load. Everis uses it to prompt support, not to label people.

What this means for your organisation

HRV gives an objective, continuous view of strain that surveys alone can't. Read carefully, against personal baselines and alongside other signals, it gives leaders an earlier view of where pressure is building, while individuals get timely, private support.

Sources: Kim HG et al. (2018); de Looff P et al. (2018). Full references on our Science page.