If you need to measure your resting heart rate, you should be completely calm. So don't do it while you're out for a walk, like the woman in the picture.

Is it really true that if you have a low resting heart rate, you’re really fit?

Many athletes have a very low resting heart rate, but that doesn’t mean that a low resting heart rate in itself means that you are in good condition, says a professor at the Norwegian School of Sports Science.

Many people use a heart rate monitor as part of their training, and consequently have the ability to monitor their heart rate continuously. If you are part of this group, you might be curious about what your resting heart rate really says about how fit you are.

“As is always true in research, the answer is not that straightforward,” says Jostein Hallén a professor at the Norwegian School of Sports Sciences.

Some people are simply born with a heart that beats slower at rest than others .

Your heart rate determines how much blood your heartbeat can supply to the body. But even if some of this is determined by your genes, you can influence your resting heart rate with exercise.

Jostein Hallén studies endurance, among other topics.

No point in comparing your heart rate to others

The resting heart rate of healthy adults is typically 50-80 beats per minute.

But if, for example, a woman has a resting heart rate of 50, that can mean either that she is very fit or that she naturally has a low resting heart rate. Or both.

So there’s no point in comparing your own resting heart rate with others, Hallén says.

But as a goal for yourself, it can be useful, the researcher said.

“If you exercise to improve your fitness, you can use your resting heart rate as a measure of whether your training is having an effect,” Hallén says.

Because the heart is a muscle with a cavity inside. And when you train to improve your fitness, you’re simply training your heart muscle.

So what’s really going on if your resting heart rate has dropped?

A quarter of a litre of oxygen

“Exercise makes the heart bigger, more elastic, and means there is more blood in your body, which means that your heart pumps more blood per beat,” says Hallén.

The blood that enters the heart from the lungs contains oxygen. And a body at rest needs a certain amount of oxygen to keep going.

Hallén gives this example for a person who is completely at rest:

A body that weighs 75 kilos requires around a quarter of a litre of oxygen per minute to keep vital processes going.

That means the heart has to pump out about five litres of blood per minute for the body to get enough oxygen, Hallén says.

And then there are two variables that count: The first is how much blood the heart manages to pump into the body per beat. The second is how often the heart beats, which is your resting pulse.

So if you have a larger heart that pumps out more blood per beat, your heart does not need to beat as often.

Your resting heart rate goes down.

Sleep has an effect

And it's not just exercise that can affect how often your heart beats at rest. An experiment on American students showed that their resting heart rate went up when they went to bed later than usual.

This effect might last until well into the next day.

A high resting heart rate can also be a sign of illness, according to the Norwegian Health Informatics website.

And here it gets complicated. A resting heart rate that is too low is not always a good sign either.

Sometimes there may be something wrong that causes the heart to beat slowly. Researchers from UiT — The Arctic University of Norway found that people who had a low resting heart rate more often had heart fibrillation, according to a 2016 study in the European Heart Journal.

But this article was not really about illness. Let's go back to the training effect.

The difference between fitness and endurance

How important is the resting heart rate for people who want to be fit? Or in other words: Is it enough that your heart is in good shape?

“You have to think about the goal of your training,” Hallén says.

He distinguishes between endurance and fitness. A low resting heart rate is a sign that you are in good condition.

But to be good at various sports, you need to train other muscles, not just your heart.

Endurance in the muscles that you need for your sport of choice is perhaps just as important, Hallén said.

“A cyclist who is in good condition will most likely have poorer endurance on the football field than a football player in poorer condition,” says Hallén.

Resting heart rate included in fitness calculator

Ulrik Wisløff, a professor at NTNU, the Norwegian University of Science and Technology, has previously argued that good fitness is a very important goal for your health.

“Fitness is one of the things that says the most about your health right now and in the future,” Wisløff has said.

He and his colleagues have created a fitness calculator based on tests they have done on participants in a study of the population of Trøndelag County, called HUNT3.

The calculator includes resting heart rate, along with age, weight and height, among other factors.

A little exercise provides great health benefits

Hallén does not doubt that good condition is good for your health, but believes it is important to include other goals.

“For people who don’t want to excel at a specific sport, it may be that getting enough exercise is a little more important than being super fit,” Hallén said.

With that in mind, you don’t have to train so hard.

“To increase your heart size, you probably need to increase your exercise level to a certain intensity, but to improve your health, it is enough to be active, without putting too great of a demand on your body in terms of the intensity,” Hallén said.

He cites a Norwegian School of Sports Science study that shows that even a few small steps per day can prolong life.

Measure your heart rate when you are active

And for those who want better fitness, Hallén believes that resting heart rate may not be the easiest thing to use as an indicator, because there is so much that can alter your pulse, even if you try to be completely calm.

Instead, he recommends doing the same activity and measuring your heart rate each time, such as running on a treadmill at a fixed speed for a given amount of time.

If you have a lower heart rate over time, that’s a good sign that your heart is able to pump more blood around the body with each beat.

Translated by: Nancy Bazilchuk.

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