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If your heart feels like it's going to come out of your mouth when you walk up the stairs or you have trouble breathing when you run to catch the bus, it might be a sign that you're not in peak physical shape.
But what happens after you finish exercising can be just as revealing about the inner workings of your body.
The heart rate recovery test (HRR) is the difference between your pulse when your heart is pumping blood at full tilt during exercise and how fast it beats about a minute later.
Cardiologist Nieca Goldberg, from the Grossman School of Medicine at New York University, in the United States, explains that HRR is a good indicator of our cardiovascular health, which can predict high blood pressure and cardiac events.
But the RFC is much more than that. Poor results can be an early warning sign. They help uncover hidden problems with the rest of the body, which, crucially, includes our risk of death in general.
In 1999, scientists at the Cleveland Clinic in the US state of Ohio published a surprising study. They examined the RFC of 2,400 adults and followed them for six years.
The team concluded that people with low heart rate recovery were about four times more likely to die than others during the study period. And since then, other teams from around the world have found similar results.
RFC has emerged as a surprisingly effective predictor of death from any cause, whether or not there is something wrong with the heart. And, among young adults and middle-aged people, HRR has an even greater relationship with the risk of death than high blood pressure.
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Here's a quick and simple way to calculate your RFC, using materials you probably already have at home.
Calculating heart rate
It's important to consult your doctor before starting a new exercise regimen.
If you experience dizziness, chest pain or tightness, or shortness of breath disproportionate to your exercise, stop immediately. This test is not appropriate for people with pre-existing heart conditions without medical supervision.
First of all, have a way to write down your data and a timer, available on most cell phones. A smartwatch or other wearable physical activity tracking device would also be useful.
Next, you need to calculate your maximum heart rate. If you have a smartwatch or other similar device, it will be able to respond. Otherwise, she is normally around 220 minus her age.
With that, it's time to exercise. Your intensity should be enough to raise your heart rate to 70 to 85% of its maximum: running, cycling or rowing, depending on your level of physical conditioning.
To calculate HRR, take your pulse immediately after you finish exercising, while you are still at your peak. The easiest way is with a smartwatch or fitness device.
Alternatively, you can also hold one of your fingers against your neck and count the beats for 10 seconds. Multiply the result by six and you will have the approximate number of beats per minute.
Then rest for a minute, sitting or lying down, and check your pulse again. Simply subtract the second number from the first and the result is your RFC.
The desired RFC
The goal is for your heart rate to return to normal quickly after you finish exercising. The faster it falls, the better.
A good heart rate recovery would be a drop of at least 18 beats in the first minute.
This number can vary from one individual to another and depends on factors such as age. But an RFC of less than 12 beats can put you at risk for health problems over time.
Early warning
The relationship between HRR and risk of death is believed to be due to the vagus nerve, a critical link between the brain and the rest of the body.
It relays signals to and from your heart, liver, intestines, and other organs, controlling whether you are in the more stressful, fight-or-flight mode, or the more relaxed, rest-and-digest state.
"We have these two systems that work in the heart, a brake and an accelerator," explains professor of exercise and health sciences Lindsay Bottoms, from the University of Hertfordshire, in the United Kingdom.
When we exercise, the accelerator (also known as the sympathetic nervous system) is activated, sending the body into "fight or flight" mode. The heart beats faster and the blood vessels dilate, allowing oxygen to be pumped to the muscles.
When we finish exercising, our body needs to cleanse the metabolic waste created during physical activity, such as lactic acid and other waste products. And this process requires oxygen.
"You need to get rid of oxygen from your muscles," explains Bottoms. "So you still need to have high blood flow and you still need to keep your heart rate high."
At the end of this process, the body applies the brakes and switches to parasympathetic mode. This is the brake that puts the body into rest and digest mode.
As our physical condition improves, our body also improves the alternation between the accelerator and brakes. This is known as higher vagal tone and is highly beneficial.
It is linked to better mental health and cognitive functions, as well as better immune health and lower levels of inflammation, among other factors. And it includes a lower risk of death.
Room for improvement
If you are concerned about your RFC, Nieca Goldberg recommends making an appointment with a doctor who can perform a full assessment of your heart risk.
The good news is that any problems that are identified can be resolved. Research has concluded that it is possible to improve HRR with exercise programs, which can reduce your risk of death to normal levels.
Bottoms and Goldberg recommend regular cardiovascular exercise to keep your cardiovascular system in tip-top shape.
"If you want to improve your heart rate recovery, try walking at moderate paces, cycling, or, if you can, slow or brisk running or swimming," explains Goldberg. You can even try dancing, she says.
And if your RFC improves, you'll really have a reason to dance and celebrate.
Important: all content in this report is provided as general information only and should not be treated as a substitute for advice from a doctor or other healthcare professional.
Read the original version of this report (in English) on the BBC Health website.
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