At a time when many children spend hours watching TV and playing with tablets, this message is extra important, one Norwegian expert says. (Illustrative image: fizkes, Shutterstock, NTB scanpix)

Children who are not physically active have poor cardiac function

A new study shows that children who are less physically active have poorer cardiac function than their more active peers. "This study is a piece of a larger puzzle, where the big picture shows that children should be less sedentary and be more active", says one of the researchers.

The 377 children who participated in the study were between six and nine years old. The researchers studied the degree of physical activity in the children and how long they were sedentary each day, along with measuring their oxygen uptake and heart function.

Their cardiac function was measured using an ECG, which shows variations in heart rate. Low heart rate variability is associated with cardiovascular disease in adults.

Ulf Ekelund, a professor at the Norwegian School of Sport Sciences, is one of the researchers behind the new study.

“We saw a connection between sitting and lower variation in heart rates, and a connection between low physical activity and lower variation. This is somewhat surprising, since we looked at young, healthy children,” says Ekelund.

Small variation in heart rates

The low variation meant that the heart signals varied little during the ECG measurement. A person’s heart rate usually varies a lot as they breathe or move. Researchers describe variations in heart rate as low or high compared to normal, where high variation is considered good when it comes to cardiovascular disease.

Ekelund emphasizes that the researchers can’t yet say for certain that these children are at increased risk of cardiovascular disease.

“We can’t say that based on this study. But what we do know is that an increased risk of cardiovascular disease has been seen in adults with low variation,” says Ekelund.

Don't know the cause

The correlation between sedentary time and low variation in heart rate was greatest in the girls in the study. For the boys in the study, the relationship between poor oxygen uptake and low variation was most clear.

Children who were very sedentary, had poor oxygen uptake and low physical activity, were clearly at greatest risk of low heart rate variation.

The researchers adjusted for body fat in their study, so they know that the differences were not due to higher body weight in the inactive children.

The researchers can’t say, however, if the lower heart function found in the more sedentary children was linked to a genetic cause.

“We can't say for sure which comes first, inactivity or heart function. Our study says that there is a connection, but can’t tell us the cause of the connection,” he said.

The researchers warned in their study that inactivity is not good for heart function.

“We have also seen in previous studies that there is a relationship between metabolic risk factors and inactivity in children of this age,” says Ekelund.

Metabolic risk factors include being overweight, having high blood pressure, high insulin levels or high cholesterol levels.

Physical activity important

Ekelund says there is no doubt that children should be physically active.

“It’s important for children’s cardiovascular function. This study is a piece of a larger puzzle, where the big picture shows that children should be less sedentary and be more active,” he said.

At a time when many children spend hours watching TV or playing with tablets, the message is even more relevant, he says.

“Spontaneous physical activity in children is very important. We need to raise awareness of this, along with parents and the schools, to prevent a public health problem,” he said.

More physical education and more free time activities are among the measures that can help.

Ekelund does not believe conditions in Norway are different than in Finland, which is where the children in the study were from.

“The results of the study are likely to apply to children across the Nordic region,” he says.

He says that children in this age group should have at least 60 minutes of activity each day. Currently, he said, 80-90 per cent of Norwegian six-year-olds meet these recommendations.

“We aren’t sure whether this is sufficient to maintain good heart health in children, but several studies seem to suggest this. However, we need more studies to understand more about the amount of activity that children need in order to be in good health,” he said.

Good habits established in childhood

Maja-Lisa Løchen is a professor of preventive medicine at the University of Tromsø and a consultant at the cardiology department at the University Hospital in Northern Norway.

“This is an interesting study that seems well done — but a cross-sectional study can only generate hypotheses and says nothing about causation. The purpose of the study is to look for a possible mechanism to explain the protective effect of physical activity,” says Løchen.

She points out that physical activity is a very important protective factor for adult heart health.

“I take it as a given that it is also very important for children, both from a pure physiological aspect, to prevent heart disease over the long term, but also to help establish good habits,” says Løchen.

Variation in heart rate

Løchen points to an American study from 2017, which looked at the importance of heart rate variability and cardiovascular disease in adults.

The study had nearly 10,000 participants and was published in the journal Annals of Epidemiology, with lead researcher Yasuhiko Kubota.

“The study showed that people whose heart rate had low variation had a significantly higher risk of cardiovascular disease, compared to those with high variation,” said Løchen.

She also describes a study from Tromsø from 2018 which showed that teens who are physically active have a more favourable fat composition than those who are less active. This article was published in the journal Acta Pediatrica.

Løchen says that a major challenge facing today's society is that children are not active enough after they start school.

“Both schools and society as a whole have a huge obligation to facilitate daily physical activity in the schools,” says Løchen.


Aapo Veijalainen et al. Associations of physical activity, sedentary time, and cardiorespiratory fitness with heart rate variability in 6- to 9-year-old children: the PANIC study, European Journal of Applied Physiology, September 2019


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