A runner’s guide to understanding heart rate variability | Canada Voices

Heart rate variability has become one of the more curious metrics to emerge from the age of wrist-worn running trackers that, if read properly, can be a nifty training insight.

HRV is one layer of complexity beyond heart rate. At its simplest, it measures the tiny fluctuations in time between heartbeats.

A person with a high heart rate variability is able to withstand an elevated heart rate during exercise and a comparatively low heart rate while resting. That is a good thing – a sign of a healthy nervous system that properly toggles between sympathetic (fight or flight) and parasympathetic (rest and digest).

The opposite, maintaining a low HRV – where your heart rate in exercise is similar to while resting – can be a sign of stress or fatigue.

For runners, HRV matters because it offers something traditional metrics cannot: an insight in individual preparedness. It’s one of the key metrics wearables use to determine your overall “readiness” score.

When HRV is low – usually because of an excessive training load, poor sleep, illness or life stress – it can act as an early-warning sign to pull back before fatigue leads to injury or burnout.

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In theory, a high HRV corresponds to a body that’s fit and ready to run. The reality is more complicated.

One of the central misconceptions about HRV is that it operates like a leaderboard. It does not. There is no universal “good” score; values vary widely between individuals, shaped by genetics, age and training history. What matters is not the number itself, but how it behaves over time.

This is where confusion often sets in for fit runners. It is entirely possible for a well-trained athlete to record a low HRV. Fitness does not inoculate against stress. In fact, heavy training loads can suppress HRV, particularly during periods of high intensity or insufficient recovery. Research consistently shows that while elite athletes tend to have higher HRV on average, those values fluctuate with fatigue and training cycles.

HRV should be treated less as a score and more as a signal. A dip in HRV might not mean you are unfit; it may simply mean you are tired, stressed or pushing too hard, too often.

That raises the natural question: Can you train your HRV?

The answer is both yes and no. You cannot train your HRV directly in the way you might chase a faster 10K time. But you can influence it indirectly by improving the systems it reflects. Regular aerobic training, hydration, good sleep and general stress management all tend to raise HRV over time.

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There is also emerging evidence that HRV-guided training – adjusting workouts based on daily readings – can improve performance more effectively than rigid plans, though the research results are mixed.

Some interventions are more experimental. Techniques such as HRV biofeedback, which train breathing patterns to stimulate the parasympathetic nervous system, have shown promise in small studies of athletes, though they remain far from mainstream.

As a competitive runner, I spend little time trying to train my HRV itself. It’s a means to an end, not an end in itself. Plus, spending too much time worrying about the score, especially when my GPS watch gives me one reading and my mattress tracker, which monitors sleep patterns, gives me a slightly different one, feels like a futile exercise. Used poorly, it becomes another number to chase, another source of anxiety. That said, an unusually low score tells me I should take my run a bit easier.

It’s a valuable proxy for how I am handling training stimulus and life stress. And yet, it is important to remember that, for all its precision, it is still only one signal among many that is best interpreted alongside running’s oldest metric: how you feel.