Resting heart rate has long been considered a critical health metric that can predict whether a person is vulnerable to heart attack, stroke, and lung disease.
The lower the score, the fitter you are said to be, as the organ works efficiently to pump blood throughout the body when you are not exercising.
Now, millions of us will be familiar with our magic number every minute of the day thanks to smartwatches that attach to our wrists.
Some devices even issue warnings if the number exceeds a certain level.
But experts have been cautious, arguing that the resting heart rate we see on our tracker isn’t as reliable an indicator of heart health as you might think.
While the NHS suggests that a resting heart rate between 60 and 100 beats per minute (bpm) is normal for adults, studies show that the ideal number can vary depending on age.
One study showed that men in their 50s with a heart rate above 75 bpm were twice as likely to die in the next 20 years, compared to those with 55 bpm or less.
The results also suggested that each additional bpm was linked to a three percent increased risk of death, a one percent increased risk of cardiovascular disease, and a two percent increased risk of coronary heart disease.
Resting heart rate, the measure of how often a vital organ beats per minute, is considered a critical health metric, which is why a dozen smart devices now offer to track it.
Meanwhile, data from the US Centers for Disease Control and Prevention (CDC) suggested that optimal cardiac fitness means having a beat per minute below 60, roughly between 47 and 57.
Only about 10 percent of people are believed to fit into this category, most of whom are professional athletes.
Other figures suggest that an athletic resting heart rate for men aged 18 to 25 is between 40 and 52 bpm, while the equivalent figure for men over 65 is 52 to 55 bpm.
The average figure for men of all ages is a bpm in the low 70s, while those in poor or below average health are considered to have a bpm in the high 70s or above 80.
For women, an athletic person ages 18 to 25 would get a resting beat per minute of 40 to 48, while an athletic woman age 65 or older would get a beat of 52 to 55 beats per minute.
An average result for women was 74 to 78 bpm at the younger end of the scale and 73 to 76 at the older end. Like men, a bpm in the 70s or above 80 for women was considered below average or poor.
While 60-100 bpm is the normal range for adults, and many smartwatches will tell you this is healthy, the general consensus is that the lower a person is within that range, the better.
For example, resting beats per minute above 100 are considered too fast for most people and could be a sign of something abnormal in the body.
Studies suggest that people with lower HR have overall better heart health, as they are generally healthier, while those with higher results are more likely to have heart disease risk factors such as high blood pressure or obesity.
Experts are keen to note that individuals vary and some people will have different “normal” resting heart rates, especially if they have an existing heart condition.
Heart rate variability (HRV), the term for the variation in time between heartbeats, is also a heart health variable that smart devices track.
Some experts consider a high HRV to be as important as resting heart rate, as it represents the organ’s ability to respond quickly to the demands placed on the body.
HRV naturally decreases as people age. Healthier people in their twenties have an HRV of about 50 to 105 milliseconds, while for people aged 60 to 65 it is typically between 25 and 45 milliseconds.
Even though smart health devices offer to monitor heart health metrics for us, experts warn that we should not rely too much on the devices as they have their flaws.
Most wearable devices track heart rate using a small sensor on the back of the device. But this means that not wearing it tight enough (or too tight) can influence the accuracy of the data.
Additionally, people with darker skin and those with tattoos on their wrists may also experience more inaccurate results.
This is because darker skin tones absorb more light, which in turn can interfere with the green light that devices use to measure heart rate.
The same happens with tattoos in the wrist area, since the substances that give them color also absorb light.
While some warning signs (pictured) are easy to spot, such as severe chest pain, others are more vague and difficult to identify.
Additionally, some devices turn off heart rate monitoring features when the battery runs out to save power.
Finally, like any device, malfunctions can occur either due to manufacturing or software faults, damage, or simple wear and tear.
It is for these reasons that doctors urge people with any symptoms of heart problems to speak to a doctor even if their smart device returns normal readings.
A device-proof way for people to monitor their resting heart rate is through the following exercise.
Place your index finger and middle finger on the inside of your wrist or on the side of your neck, just below your jaw.
Once you find your pulse, count the number of beats over the next 60 seconds to get a bpm figure.
For more accurate results, it is recommended that people perform this test at rest, that is, sitting or lying down.
Experts also advise against drinking coffee or nicotine before measuring your pulse, as these substances can artificially increase your heart rate.
For accuracy, complete the test at the same time each day to obtain an average over time.
Another heart health metric that devices frequently measure is target heart rate (THR), which is a measure of how fast the organ should beat during exercise.
THR is calculated by first subtracting your age from 220 bpm and then taking this figure and calculating what 50 and 70 percent of it is.
For example, a 50-year-old person will have a THR between 85 and 119 bpm.
Some experts raise this to between 50 and 85 percent of 220 bpm minus age, although the British Heart Foundation (BHF) recommends the range of 50 to 70 percent, which also has a free tool you can use to discover yours.
Those who want to keep their heart in shape use a THR range to ensure they are performing the optimal level of exercise. For example, a runner who does not reach his THR while running knows he needs to pick up the pace.
Exercising at a THR beyond the upper limit of what is recommended can be dangerous.
Those who do not have a smart device to track their heart rate while exercising are recommended to take what is known as the “talk test” while exercising.
If you can still talk while doing the exercise but you also feel hot and breathing a little heavier than normal, you are working at the right pace.
But if you can’t talk at all, you may be doing too much.
As always, doctors urge people to listen to their bodies and, if an exercise feels uncomfortable, to stop.
While not as accurate as specific medical equipment, experts say devices that track heart rate can be useful as patients may be inspired to go to a doctor for advice and any potentially concerning results can be properly investigated.