While there's a swathe of metrics and gadgets that can measure more elements of your biology than you can imagine, the humble heart rate can tell you much about what’s going on under the hood.
A 2024 study in the journal Scientific Reports noted that heart rate “reflects the health of the cardiovascular system, metabolic rate, and activity of the autonomic nervous system” – three of the biggies when it comes to overall health and fitness.
But what signals of your heart’s beats per minute (bpm) are worth listening to?
Listen to your heart
“Resting heart rate is related loosely to how long you live for,” says consultant cardiologist Dr Mark Dayer. He explains that historically, a resting heart rate between 60 and 100bpm has been considered normal, “but that's a somewhat old–fashioned view”.
“We know that higher heart rates are associated with less good survival than lower heart rates, and so there's probably something wrong with someone with a resting heart rate of 100, whereas someone with a resting heart rate of 60 is probably okay,” he adds.
There’s long–term scientific research that backs up this assessment too. That same article published in Nature in 2024 looked at the data from three landmark studies and consistently found that subjects with a lower resting heart rate of 60bpm had a significantly longer life span than those with a resting heart rate over 90bpm.
In one study among French men, this translated to an average difference of nine years, while another that was based on American women showed a life–extending boost of five years.
“[That’s] quite a long time in terms of life expectancy,” adds Dayer. “If you could increase your life expectancy by five years, that would make far more headlines than a tablet that doubles your survival from six months to one year in pancreatic cancer.”
Run low
Athletes are renowned for having much lower resting heart rates. Five–time Tour de France champion Tadej Pogačar has a resting heart rate of 37bpm, while fellow member of the five club Miguel Indurain’s was reported to go as low as 28bpm.
“Lots of people have slow heart rates. Athletes tend to have lower heart rates, and lower heart rates tend to be associated with survival,” says Dayer.
“Although we say less than 60 is abnormal, if you're dealing with young, fit people – even those going to Parkrun – many of them will be in the 40s and 50s.”
The reason for these low readings is two-fold. Exercise training, particularly endurance–based activities such as cycling, increase vagal tone – the baseline activity of the vagus nerve, which is the physical brake on your nervous system and keeps the parasympathetic (rest and digest) nervous system dominant over the sympathetic (fight or flight) and therefore resting heart rate low.
Also, like with any muscle, the heart gets bigger and stronger with exercise stimulus, meaning it can pump out higher volumes of blood with every contraction. “At rest, they're just ticking over, so they don't need to do very much,” says Dayer.
A low resting heart rate can be an indicator of disease and illness, though, if you’re not athletic and you feel unwell; other symptoms include breathlessness, swollen ankles or struggling to sleep at night.
“The reason why there is cause for concern is that you can get what's called heart block,” says Dayer. “In some people, not every stimulus from the top of the heart (atria) gets through to the bottom part of the heart (ventricle), and then your heart rate can slow.
"If none of the signals get through, then your heart rate can go really slowly – in the 20s, although some have higher heart rates in the 30s and 40s. That's called complete heart block and then you need pacemakers.”
Max out
At the other end of the scale is your maximum heart rate. The physiological limit of your heart’s ability to pump blood round your body, when you reach this ceiling, you can’t sustain it for long and it’s the ultimate anaerobic effort – causing your muscles to break down glucose without oxygen before they’re eventually flooded into submission by the byproduct of lactic acid.
Your maximum heart rate alone can’t tell you much about your health and fitness compared to others, though. “Everybody's different, so there's quite a lot of variation,” says Dayer.
After peaking in early childhood (where maximum heart rate can exceed 200bpm), there is a natural, gradual decline that not even the Pogačars of this world can completely halt in its tracks.
But Dayer adds that if you haven’t exercised for a while and you start again, often your maximum heart rate recovers a bit.
“When I got back into exercising in my mid-40s, initially my maximum heart rate was about 160bpm and after a few years of proper exercise rather than just a bit of Parkrun, it got up to about 170bpm, but it's gradually declined again over time.”
Dayer notes that the key thing with maximum heart rate is how you calculate it, with the ‘220 minus age’ formula plastered everywhere set by “a group of people back in the 70s who pulled some random data together”.
He adds that you’re better off using a different equation, such as the Fairbairn Formula: 208 minus (0.8x age) for men; 201 minus (0.63x age) for women, or better still, “going off and doing a 5km flat out – that will probably tell you what your maximum heart rate is”.
Keep in reserve
The benefit of knowing your maximum heart rate is it enables you to work out your heart rate reserve (maximum heart rate – resting heart rate).
This reserve can be used to establish heart rate reserve–based training zones – a more precise method that takes aerobic capacities into account rather than going solely off the maximum heart rate.
“It’s important for determining your exercise capacity, but it's complicated,” cautions Dayer. “The amount of blood your heart pumps is your heart rate times the amount of blood your heart ejects every time it beats, so if you've got a slightly bigger heart, it's going to eject more blood each time it beats.
"But it has got to pump it somewhere – it's got to go into the muscles and be used by the muscles and everything else.
“You can't assume the heart in itself in isolation is describing all this, and it's the most important thing; it's the whole system.
"You’ve got to have the lungs to get oxygen into that volume of blood going through the system, you've got your brain on top of that, which may or may not be holding you back, depending on who you believe. There's a whole series of breaks and limits, of which the heart is only one part.”
Shifting sands
One metric that Dayer thinks there are still question marks over in its application among everyday athletes is heart rate variability.
A measure of the marginal difference between each heartbeat, companies such as Whoop have built whole products on HRV, with claims it can show when you’re not in peak health and need to rest (a low HRV) or you’re fighting fit and ready for a hard workout.
“It's complicated because it relies on really precise measurements, so your HRV from your watch, ring or Google Fitbit Air is going to give you an approximation,” says Dayer.
“The second thing is that it's kind of dependent on your resting heart rate. A variation of 50 milliseconds is going to be quite a lot as a proportion of a heart rate higher than 100, whereas if your heart rate's 40, it's a much lower proportion of that gap.
"We're not quite sure whether to adjust it for resting heart rate or not, and we're not quite sure what normal values are, and there's big variation between people.”
He concludes that the best measure of whether you should train or not is to look back at your training log and see how you feel.
“If you're ever relying on one metric, you're usually going to come unstuck; relying just on your HRV to determine when you're fit to train is probably not great.
"Use it sensibly as part of your overall evaluation, remember yours is specific to you, don't compare to other people, and learn how it varies with you and what you do before you pay too much attention to it.”
Getting the measure
Finding out any heart rate metric requires a monitor. Fortunately, they’ve never been more readily available or convenient to use, with most smart watches having an optical sensor built in to take readings whether resting or working out.
But Dayer warns to take their findings with a pinch of salt. “Usually the overnight resting heart rate is reasonably accurate if it's done over a long period of time, but smartwatches can misread, under or over read heart rates.
"It relies on shining bits of light in and measuring the reflections, and you can get misreadings if your watch isn't on properly, you've got tanned skin, or you've got lots of hair on your arms among other things.
He recommends chest straps such as the Polar H10 – ”it’s very good and has been validated” – as a more accurate alternative.
And before you’re alarmed by any readings, he concludes that “if you're feeling alright, you probably are”.
