As the popularity of smartwatches, also called wearables, increases, so too does the amount of data users can access about their health.

Statistics like resting heart rate, V02 max (maximal oxygen consumption) and heart rate variability (HRV) provide valuable insight into your fitness levels.

But not all measurements are created equal.

While HRV has long been used by elite athletes to dictate their training schedule, it has become a “buzzword” among the broader community.

Matthew Ahmadi, deputy director of the University of Sydney’s Mackenzie Wearables Hub, says HRV has been around for more than 20 years in the competitive sports environment.

“Over the past 10 years or so, it has really picked up among the general population, mainly due to increases in the use of wearables,” Dr Ahmadi says.

WHOOP, a leading wearable brand and official partner of the Women’s Tennis Association, has been collecting data on the most consistent factors that boost or harm your HRV.

Global statistics from 2024 show that getting quality sleep, consuming caffeine and having a consistent wake time are most likely to improve your HRV, while consuming alcohol, being sick and highly stressed will see your numbers crash.

So just what does HRV measure, and how might you use it to maximise your workouts?

HRV indicates how ‘balanced’ your autonomic nervous system is

Dr Ahmadi explains that HRV measures the “variation between heartbeats”.

The heart does not beat consistently (like a metronome or clock).

So, while your heart might be beating at 80 beats per minute, there will be longer or shorter gaps between each heartbeat.

How variable these gaps are determines your HRV, with a higher number indicating greater variability.

A high number is ideal, and an indication that the body is in homeostasis (or balanced), Dr Ahmadi says.

This is because HRV is a window into the autonomic nervous system.

The autonomic nervous system consists of two main divisions: the parasympathetic and sympathetic nervous systems.

In simplistic terms, the parasympathetic nervous system is responsible for ‘rest and digest’ processes, while the sympathetic nervous system is responsible for ‘fight or flight’ responses.

Ideally, Dr Ahmadi says, the two are in balance, meaning the body is equally responsive to both inputs.

“The more fit someone is, the more their body is able to adapt to different stressors and therefore recover better,” he says.

But if your HRV is low, it indicates that one branch of the autonomic nervous system is dominating:

“It generally means your sympathetic system is dominant, so your body is on high alert.”

HRV indicates how ‘ready’ you are to exercise

When your HRV is measured is also critical to its interpretation.

Measuring it before you go to bed will tell you how well the body has recovered from the current day’s activities or stressors, Dr Ahmadi says.

“[Measuring HRV] right after you wake up will give you a good indication of what your body is prepared to handle over the coming day,” he adds.

This is the key reason HRV offers an advantage over other measures of fitness.

Not only does a higher HRV indicate a higher level of fitness, it can also be used to dictate what level of intensity you should take on in your current day’s exercise regime.

“In the sport science world, we think of HRV as a proxy for ‘readiness’ [to train],” Kristen Holmes, WHOOP’s principal scientist, says.

WHOOP uses HRV to determine its users’ daily “recovery” scores, grading them as being in the green, yellow or red.

On green days, WHOOP encourages users to go “all out”, while on a red day, it recommends “active recovery” activities like meditation, light walking or yoga.

Many elite athletes similarly use HRV to adapt their exercise regimes, with research showing those who do so achieve better performance outcomes.

Factors that improve or decrease HRV

WHOOP also collects data on the most common positive and negative influences on HRV.

Positive factors include being well-hydrated, following a healthy diet, getting quality sleep and keeping consistent sleep and wake times.

“That’s what makes it both a great measure and really frustrating,” Dr Holmes says.

“It’s hard sometimes to pinpoint exactly what isn’t allowing me to respond and adapt to external stressors in a functional way.”

There are, however, consistent factors that lower HRV, with the top being the consumption of alcohol.

In fact, Dr Holmes says alcohol is such an “HRV crusher” that 89 per cent of people who use the platform report decreasing alcohol consumption in the long term.

“That’s because people can directly see the performance cost from their behaviours,” Holmes says.

“Your coach can tell you, ‘Hey, alcohol is really bad for your performance’, but until you see directly how it affects your HRV, you’re like … wow, I’m a lesser version of myself today. It’s sobering.”

But you should avoid comparing your HRV scores to others’.

Generally, the older you get, the lower your HRV will be, while women also tend to have a lower HRV on average.

If you want to improve your HRV, both Dr Ahmadi and Dr Holmes instead advise taking a baseline level and judging any changes relative to your own scores.

Don’t panic if your HRV is low

It’s also important to note that a low HRV is not always bad.

As one example, Dr Ahmadi says that you should expect to see a drop-off in your HRV if you are beginning a new exercise program, especially if you were previously sedentary.

“The first few weeks, you’re likely to see a big decrease in your HRV on a daily basis,” he says.

“But ideally, if the program is working the way it should be, you should start to see your HRV increase over the coming weeks and months, and then taper off as your body adapts to the current program’s load.”

Once your HRV starts to stabilise, it’s a good indication that you are ready to “progress” your program.

But if you don’t see an improvement in your HRV, it’s likely you need to take your foot off the pedal.

“If you see a big drop-off, then it’s a good idea to not push as hard the following day, because your body is giving you signs that it needs time to recover,” he says.

“As you settle into a new training regime, your body will adapt and you’ll be able to handle higher stress and workout loads closer together.”