The lack of CRF in children is very concerning because of its association with short and long-term health consequences, says Geetha Raghuveer, MD, MPH, a cardiologist at Children’s Mercy Hospital and a professor of pediatrics at the University of Missouri, both in Kansas City, Missouri, and the chair of the writing committee for the statement. “The immediate effects of poor fitness are related to changes in heart function and blood vessel function, which over the long term can result in premature cardiovascular disease,” says Dr. Raghuveer. There is also evidence of a bidirectional relationship between obesity and CRF, she says. “Obesity results in low fitness, and low fitness can also contribute to obesity, which is associated with comorbidities such as type 2 diabetes, hypertension, and cardiovascular disease,” says Raghuveer. “Staying fit has a wide range of benefits that go beyond physical health; it’s also positively associated with emotional and mental well-being,” she says. The AHA statement identified a downward trend in CRF both internationally and in the United States. They found that:
The number of boys ages 12 to 15 with a healthy CRF declined from 65 percent in 1999–2000 to 50 percent in 2012.The number of girls ages 12 to 15 with a healthy CRF declined from 41 percent to 34 percent during that same time.Only 1 in 5 youth with obesity, defined as having a BMI of 30 or higher, has a healthy CRF.
RELATED: What Counts as Aerobic Exercise?
Lack of Fitness in Young People Is Linked With Disease Risk and Early Death
Historically, the concern about the health risks associated with lack of fitness has been in adults — typically, when a person reaches adulthood their lifestyle changes because of jobs and other social determinants, and they become more sedentary, says Neel P. Chokshi, MD, the medical director of sports cardiology and fitness and an associate professor at Penn Medicine in Philadelphia. “This paper points out that kids may be at risk for those same issues now — they aren’t at the same level of fitness as in the past. Maybe we should be targeting more interventions around cardiorespiratory fitness to prevent them from developing these diseases in adulthood,” he says. In the past few decades, more data has been published about the importance of cardiorespiratory fitness in predicting risk for adverse health outcomes. In some studies, CRF was a stronger predictor of adverse health outcomes than factors such as high blood pressure, smoking, obesity and type 2 diabetes, according to a policy statement from the AHA published in Circulation in 2013. Many retrospective studies have found an association between CFR and chronic diseases and early death, but the link has been made in prospective studies as well, says Raghuveer. One of the largest studies was published August 2016 in the International Journal of Epidemiology. It followed 1,317,713 men with a median age of 18 for an average follow-up period of 29 years. Aerobic fitness was measured by an electrically braked cycle test. Investigators found that those who were in the lower categories of fitness at the beginning of the study had eventual premature cardiovascular disease and stroke, says Raghuveer. Researchers concluded that low aerobic fitness in late adolescence is associated with an increased risk of early death, and that the risk of early death was higher in fit obese people than in unfit normal weight individuals.
Increased Screen Time, Less Exercise, and Poor Nutrition May All Contribute to Lower Aerobic Fitness in Children
The statement authors tried to pinpoint why fitness might have decreased over the last few decades, says Raghuveer. “One of the biggest contributors to lower CRF in young people is that physical activity has decreased among young people,” she says. A study published in Pediatrics journal in January 2019 found that physical activity remained relatively stable until about 8 years of age, but dropped off significantly by age 11. This problem doesn’t just exist in the United States; in a 2019 report, the World Health Organization found more than 80 percent of children aged 11 to 17 worldwide don’t meet the current recommendations of at least 60 minutes or more of physical activity each day. Increased screen time, poor nutrition, and more sitting may also play a role in reduced fitness, but there needs to be more research on this, says Raghuveer. Social, economic, and environmental factors exist that contribute to disparities in fitness, according to the authors. “It can be difficult for many kids to access green spaces and playgrounds. Depending on the stressors, it may be more difficult for some families to have the time or money to emphasize athletics or physical activity,” says Dr. Chokshi. “Something as basic as access to childcare can make a big difference. Without it, a family may be forced to utilize more screen time and less activity,” he says.
How Cardiorespiratory Fitness Is Measured
CRF is also known as aerobic capacity or aerobic fitness, and it generally refers to a person’s overall physical capability and ability to exercise, according to Chokshi. Whereas physical activity is a behavior, a person’s CRF can be a reflection of both an individual’s past physical activity and current ability to be physically active. “The way CRF is measured in a technical sense is by a VO2 test. An individual is put on a treadmill or bike while wearing a mask,” says Chokshi. “Then we measure all the oxygen they’re breathing in and all the carbon dioxide they’re breathing out, and by doing that we can accurately assess how efficiently their body can utilize oxygen,” he says. “During the test we’ll have them increase their activity level on the treadmill to see what is the maximal capacity that they can perform,” he says. That maximum is called VO2max, and is considered the gold standard of how to measure overall fitness, according to UC Davis Health Sports Medicine. Being able to measure CRF this way is important from a science and research standpoint, but there are many other ways to measure CRF in young people that don’t involve measuring oxygen and carbon dioxide and can be performed at school, says Chokshi. The 20-meter shuttle run is the most widely used CRF test in the world, according to the study. During the test, the student runs between lines that are 20 meters apart, and the scores are based on the number of laps run.
Children Should Be Encouraged to Be More Active
The CDC recommendations include the following for increasing activity in children:
Adults can set a positive example by leading an active lifestyle.Make physical activity part of your family’s daily routine by taking walks or playing active games together.Equipment such as balls or bicycles can encourage physical activity.Instead of watching television after dinner, encourage kids try to find fun activities such as walking, playing chase, or riding bikes.
“It’s important to keep in mind that a child who appears healthy may have poor cardiac fitness. It is not just those with heart disease or asthma that we need to be concerned about,” says Raghuveer. Raghuveer believes more children should be tested, even if it’s at school and not in a doctor’s office. “This information would be useful to include along with what we already get — height, weight, BMI, and sometimes cholesterol levels or blood pressure — but those aren’t good indications of how fit the child is,” she says. The schools that currently do CRF testing could report their results to doctors’ offices, says Raghuveer. “Schools could pass information to the child’s doctor, just as we share immunization records with them; having this information in silos doesn’t help anyone,” she says. If parents are concerned about their child’s CRF, they don’t necessarily need to seek out a fitness test, says Chokshi. “The important message this paper highlights is that we need to encourage children to be more active for health reasons and for overall well-being,” he says.
