Beat by beat: Can you rely on heart-rate monitors?

Beat by beat: Can you rely on heart-rate monitors?

Heart-rate monitors are commonly worn by athletes but how accurate are the readings, asks Peta Bee.

WHEN was the last time you checked your heartbeat? Heart-rate monitors are no longer used just by Olympians and elite athletes. 

In April, a report on the global market for such devices published by Market Research Future predicted a 13.5% in sales by 2023.

It’s no surprise given that health experts tell us a high heart-rate can be a warning of rising stress levels or potentially serious heart problems. So, if you aren’t already using one, is a heart-rate monitor your key to a healthy life?

A resting heart rate (the number of times your heart beats a minute at rest) varies substantially between individuals, but for an average adult it is usually somewhere around 60-100 beats per minute, says Angie Brown, medical director at the Irish Heart Foundation. 

It’s influenced by age and genetics, but also by physical fitness and the fitter you are, the lower it is as your heart becomes more efficient with each beat it makes.

“Highly-trained athletes may have a resting heart rate below 60 beats per minute, sometimes reaching 40 beats per minute,” she says.

Exercise or anxiety will increase your heart rate and any infection or fever could also send it to above normal levels. 

Factors such as fatigue and what you eat or drink (caffeine in sports and energy drinks can send your heart rate soaring, for example) can also influence resting heart rate.

“Some people will have faster heart rates particularly after drinking coffee or after alcohol and at rest they could be at the upper end of normal at 90-100 beats per minute,” she says.

Beat by beat: Can you rely on heart-rate monitors?

Why does it matter? “Anyone with an irregular heart rate, a slow or fast heart rate, particularly associated with symptoms of dizziness, chest pain or breathlessness needs to see their GP,” Brown says.

That’s because, in recent years, scientists have found a person’s resting heart rate carries more weight in the prognosis of ill health than previously thought. 

Some have found that even a resting pulse rate at the upper end of the normal range for an adult is indicative of a higher risk of heart disease and strokes.

Earlier in the year, a paper published in the British Medical Journal’s Open Heart journal, suggested that middleaged men with a resting heart rate of 75 beats per minute could be at double the risk of death from coronary heart disease and cardiovascular disease. 

According to the Swedish research team which tracked almost 800 men for 21 years, as the men got older, every additional beat increase over 75 beats per minute was associated with a 3% raised risk of death and a 2% higher risk of coronary heart disease.

Brown says that resting heart rate is a marker of sympathetic overactivity, which is associated with an increased risk of cardiovascular events.

“People with higher resting heart rates were more likely to be current smokers, have more often a sedentary lifestyle and mental stress, higher body-mass index, wider waist circumference, higher systolic and diastolic blood pressure,” says Brown.

They were also more likely to have a medical history of hypertension, hyperlipidaemia and diabetes than participants in the lower resting heart rate group.

Keeping tabs on your ticker isn’t always straightforward. You can use the old-fashioned finger on pulse method, but it is prone to poor technique.

“Heart-rate monitors vary a great deal in their accuracy particularly during vigorous activity,” Brown says.

“They don’t diagnose rhythm disorders, to do this an ECG is needed. Although there are some phone apps and other devices that give an ECG trace which can be more useful in diagnosing arrhythmias.”

In general, apps and trackers are a useful rough guide, but the gold standard is a chest-strap heart-rate monitor which sits closer to the heart and is less prone to sliding around, so provides a more reliable reading.

Wrist-worn monitors are improving in their accuracy, but studies have found them to fall short. In a 2016 paper published in the journal JAMA Cardiology, researchers from Cleveland’s Heart and Vascular Institute found none of four wrist-worn devices was as accurate as the chest heart-rate monitor.

Beat by beat: Can you rely on heart-rate monitors?

Where heart-rate monitors have additional uses is to find out how hard you are working at the gym.

Each of us has a maximum heart rate, a point at which our heart can’t work any harder, and while the old-fashioned way of determining it — subtracting your age from 220 — has been found to overestimate or under-estimate individual results by up to 15 beats per minute, it remains a useful calculation.

“We would often calculate the maximum predicted heart rate with exercise by subtracting your age from 220,” Brown says.

However, it depends not only on your age and fitness but also if there are any underlying medical problems. If in doubt it is a good idea to check with your doctor before starting any exercise programme.

Wear a heart-rate monitor to the gym and the aim is to spend at least some time each week, if not each session, pushing to get your heart rate up to 70% to 85% of your maximum when calorie burning and fitness returns reach a peak.

Heart-rate monitors, such as Polar and Myzone, are creeping into gyms around Ireland.

US-based brand Orangetheory Fitness is taking things one-step further, offering a range of heart-rate monitored interval training classes in which you are required to strap a monitor around your arm before joining in. 

Your personal profile is displayed on a screen in class, the motivation being that is no room for slackening off at the back of the room when your scores are up there for everyone to see.

The message? Monitoring your heart is the new route to super fitness and super-health.

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