New Federal Exercise Recommendations

The New York Times

Very Brief Workouts Count Toward 150-Minute Goal, New Guidelines Say

New federal exercise recommendations include the first-ever federal activity parameters for 3-year-olds, as well as a few surprising omissions.

CreditJeenah Moon for The New York Times

As of Monday, the United States has new federal physical-activity guidelines. The new guidelines, which represent a scientific consensus about how much and what types of physical activities we should complete for good health, bear a strong resemblance to the existing, 10-year-old governmental recommendations. But they also feature some important updates and expansions, including the first-ever federal activity parameters for 3-year-olds, as well as a few surprising omissions.

And they offer a subtle, admonitory reminder that a substantial majority of us are not moving nearly as much as we should.

The idea that the government might suggest how much we need to exercise is relatively new. The first federal exercise recommendations were released in 2008, after several years of scientific background study.

 

During that time, an advisory board of researchers, most of them from academia, scoured the available scientific literature for clues about the relationships between physical activity and health and how much and what types of exercise seemed best able to lengthen people’s life spans and reduce their risks for disease.

Using that information, they assembled and presented a scientific report to the Department of Health and Human Services, which used it as the basis for the original 2008 guidelines.

Most of us probably know what those guidelines suggested.

In essence, they called for adults who are not disabled to complete at least 150 minutes a week of moderate-intensity exercise, such as brisk walking or other activities that raise people’s heart rates and breathing to the point that they can talk to a companion but cannot, should they be so inclined, sing.

The guidelines also noted that 75 minutes of vigorous exercise, such as jogging, would be equally effective but that the exercise, whatever its intensity, should take place in nonstop bouts of at least 10 minutes at a time and preferably every day.

Adults were urged, too, to do some type of strength training twice a week, while children older than 6 and teenagers were told to exercise moderately for at least 60 minutes a day.

 

That was 10 years ago. Since then, exercise scientists have published a mountain’s worth of new research about the health effects of physical activity — and of sitting — and of how much time we really need to spend in motion.

So two years ago, the Department of Health and Human Services convened a new panel of scientific advisers to sift through this research and provide updated exercise recommendations.

Earlier this year, that group delivered a 779-page scientific report to H.H.S., from which the new recommendations were devised.

To the surprise of some scientists and other observers, these guidelines, which were published on Monday in JAMA, are broadly the same as the previous set.

Again, they call for adults to complete at least 150 minutes of moderate-intensity exercise or 75 minutes of vigorous activity every week, along with strength training twice a week.

They also suggest balance training for older people and, for the first time, urge kids between the ages of 3 and 5 to be active for at least three hours a day, an acknowledgment that even small children run the risk of being too sedentary these days.

 

The most substantive change in the new recommendations involves how long each bout of exercise should be. The new guidelines say they do not need to last for 10 minutes.

Any physical activity, no matter how brief, including walking up stairs or from the car to the office, provides health benefits, according to the new guidelines, and counts toward exercise goals.

Using these parameters, “it will be much easier” for people to accumulate the desired 150 weekly minutes of moderate activity, says Adm. Brett Giroir, the assistant secretary for health at H.H.S., who oversaw the development of the formal guidelines.

This idea is captured in a new H.H.S. website cheerfully titled “Move Your Way” that summarizes the latest guidelines.

But despite this expansiveness, the 2018 recommendations do not cover some types or aspects of exercise, including high-intensity interval training. Although these brief, intense workouts are popular and widely studied, the guidelines’ writers felt that more research was needed about their safety and effects.

For the same reason, the guidelines do not set a target for how much — or little — time people should spend sitting or how many steps they should take each day, instead reiterating that the best goal is 150 minutes a week of activity.

Helpfully, the new guidelines do include some practical proposals for increasing exercise, including having health care workers ask people about their exercise habits during every appointment and employers promote physical activity at work.

But such efforts are voluntary, of course, and may be unable to overcome the greatest challenge facing the implementation of the new guidelines, which is us.

Despite 10 years of hearing that we should be moving more, few of us are.

Only about 20 percent of American adults meet the existing recommendations, and a third never work out at all, statistics show.

But Admiral Giroir says he believes that the new guidelines can and should inspire large numbers of people to get moving.

“They are so simple,” he says. “You can walk, dance, mow your lawn, park your car a little farther away. It all counts and could really make an impact on people’s health.”

Kids’ Brainpower Tied to Exercise, Sleep and Limited Screen Time

The New York Times

At least 60 minutes of physical activity a day, nine to 11 hours of sleep a night, and no more than two hours a day of recreational screen time were tied to higher mental test scores.

Researchers tied three behaviors to higher scores on tests of mental ability in children: at least 60 minutes of physical activity a day, nine to 11 hours of sleep a night, and no more than two hours a day of recreational screen time.

The new study, in Lancet Child & Adolescent Health, included 4,524 children ages 8 to 11 who were assessed with six standard tests that measure language skills, memory, planning ability, and speed at completing mental tasks.

Compared with those who met none of the three behavioral criteria, those who met all of them scored about 4 percent higher on the combined tests. Meeting the requirements for both screen time and sleep was associated with a 5.1 percent increase in scores compared with those who met neither. Only 5 percent of the children met all three criteria, and nearly 30 percent met none.

“It may be that screen time is affecting sleep,” said the lead author, Jeremy J. Walsh, a postdoctoral fellow at the University of British Columbia. “Sleep is a critical behavior for shaping our brains. Kids need to be sleeping nine to 11 hours a night for their cognitive development to be optimal.”

How Exercise Helps Reduce ADHD Symptoms

Health Central

iStock-541272034.jpg
Credit: iStock

According to a number of recent studies, exercise, especially if it’s aerobic, can reduce symptoms of attention deficit hyperactivity disorder (ADHD). Researchers are still working to identify the exact causes of ADHD, but it is generally thought to be caused by an imbalance of chemicals in the brain.

Scientists think that ADHD symptoms are caused by a deficiency in the chemicals norepinephrine and dopamine, which “play essential roles in thinking and attention,” according to the National Institute of Mental Health.

Stimulant medications are effective because they increase these chemicals, therefore reducing ADHD symptoms and increasing an individual’s ability to focus. Exercise increases dopamine, norepinephrine, and serotonin levels in the brain, which means exercise can have the same effect on the brain as stimulant medications.

In recent years, a number of studies have backed up the idea that exercise helps decrease ADHD symptoms.

study published in the Journal of Abnormal Child Psychology in 2015 looked specifically at the effects of aerobic exercise on children with ADHD. Children were enrolled in a before-school exercise program for 12 weeks. Parents and teachers provided ratings of ADHD symptoms, including inattentionhyperactivity, and impulsivity as well as ratings for oppositional behavior, moodiness, and social interactions. At the end of the trial, researchers noted reduced impairment at school and at home. Betsy Hoza, the lead researcher believes the study showed that before-school exercise could be a way of managing ADHD symptoms.

study published in Current Psychiatry Reports indicated that sustained exercise programs benefited children with ADHD, specifically by enhancing neural growth and development, and improving cognitive and behavioral functioning. Executive functioning skills, which are often difficult for people with ADHD, were found to improve after exercise.

Another study assigned some students to a nine-month after school physical activity program. Other students were placed on a waitlist as a control group. The researchers found that students who actively participated in the physical activity program had better results on cognitive performance and had better brain function on tasks requiring executive function skills.

Dr. John Ratey, M.D., the author of “Spark: The Revolutionary New Science of Exercise and the Brain,” has advocated for exercise as a supplemental treatment for ADHD. Dr. Ratey discussed the study with Medscape Medical News and reported there have also been research in Taiwan and China supporting exercise for children with ADHD.

The study from China also found that balance training might be of benefit. Dr. Ratey explains that exercise increases dopamine and norepinephrine levels, which in turn decrease ADHD symptoms. “It also raises serotonin and all these other factors in the brain that really make for a nice recipe for an exercise pill, if we had such a thing,” Dr. Ratey said.

Besides improving cognitive functioning and executive functioning skills, exercise helps by:

  • Decreasing restless energy
  • Lowering stress levels
  • Improving concentration

In the studies, researchers mostly used aerobic exercises, such as running, cycling, and using elliptical machines, because this type of activity is known to increase the neurotransmitters in the brain.

Yoga might also help. In a review of studies, yoga was found to be effective as a supplemental or alternative therapy, with similar results as biofeedback or relaxation training for those with ADHD.

One of the major differences between exercise and medication in treating and managing ADHD symptoms is that the benefits from exercise are short-lived. It is recommended that a person continues to exercise to maintain benefits, and unfortunately, it isn’t always possible to stop what you are doing every hour or two to engage in aerobic exercise. However, building exercise into your everyday routine at a time that works for you can help to keep you consistent.

Eileen Bailey is a freelance health writer. She is the author of What Went Right: Reframe Your Thinking for a Happier Now, Idiot’s Guide to Adult ADHD, Idiot’s Guide to Cognitive Behavioral TherapyEssential Guide to Overcoming Obsessive Love, and Essential Guide to Asperger’s Syndrome. She can be found on Twitter @eileenmbailey and on Facebook at eileenmbailey.

Published On: Sept 19, 2017

How Exercise Helps Reduce ADHD Symptoms

Healthcentral https://www.healthcentral.com/article/exercise-reduces-adhd-symptoms

iStock-541272034.jpg
Credit: iStock

According to a number of recent studies, exercise, especially if it’s aerobic, can reduce symptoms of attention deficit hyperactivity disorder (ADHD). Researchers are still working to identify the exact causes of ADHD, but it is generally thought to be caused by an imbalance of chemicals in the brain.

Scientists think that ADHD symptoms are caused by a deficiency in the chemicals norepinephrine and dopamine, which “play essential roles in thinking and attention,” according to the National Institute of Mental Health.

Stimulant medications are effective because they increase these chemicals, therefore reducing ADHD symptoms and increasing an individual’s ability to focus. Exercise increases dopamine, norepinephrine, and serotonin levels in the brain, which means exercise can have the same effect on the brain as stimulant medications.

In recent years, a number of studies have backed up the idea that exercise helps decrease ADHD symptoms.

study published in the Journal of Abnormal Child Psychology in 2015 looked specifically at the effects of aerobic exercise on children with ADHD. Children were enrolled in a before-school exercise program for 12 weeks. Parents and teachers provided ratings of ADHD symptoms, including inattentionhyperactivity, and impulsivity as well as ratings for oppositional behavior, moodiness, and social interactions. At the end of the trial, researchers noted reduced impairment at school and at home. Betsy Hoza, the lead researcher believes the study showed that before-school exercise could be a way of managing ADHD symptoms.

study published in Current Psychiatry Reports indicated that sustained exercise programs benefited children with ADHD, specifically by enhancing neural growth and development, and improving cognitive and behavioral functioning. Executive functioning skills, which are often difficult for people with ADHD, were found to improve after exercise.

Another study assigned some students to a nine-month after school physical activity program. Other students were placed on a waitlist as a control group. The researchers found that students who actively participated in the physical activity program had better results on cognitive performance and had better brain function on tasks requiring executive function skills.

Dr. John Ratey, M.D., the author of “Spark: The Revolutionary New Science of Exercise and the Brain,” has advocated for exercise as a supplemental treatment for ADHD. Dr. Ratey discussed the study with Medscape Medical News and reported there have also been research in Taiwan and China supporting exercise for children with ADHD.

The study from China also found that balance training might be of benefit. Dr. Ratey explains that exercise increases dopamine and norepinephrine levels, which in turn decrease ADHD symptoms. “It also raises serotonin and all these other factors in the brain that really make for a nice recipe for an exercise pill, if we had such a thing,” Dr. Ratey said.

Besides improving cognitive functioning and executive functioning skills, exercise helps by:

  • Decreasing restless energy
  • Lowering stress levels
  • Improving concentration

In the studies, researchers mostly used aerobic exercises, such as running, cycling, and using elliptical machines, because this type of activity is known to increase the neurotransmitters in the brain.

Yoga might also help. In a review of studies, yoga was found to be effective as a supplemental or alternative therapy, with similar results as biofeedback or relaxation training for those with ADHD.

One of the major differences between exercise and medication in treating and managing ADHD symptoms is that the benefits from exercise are short-lived. It is recommended that a person continues to exercise to maintain benefits, and unfortunately, it isn’t always possible to stop what you are doing every hour or two to engage in aerobic exercise. However, building exercise into your everyday routine at a time that works for you can help to keep you consistent.

How Exercise Can Boost Young Brains

Photo

Researchers studied participants in an after-school exercise program.
Researchers studied participants in an after-school exercise program.Credit L. Brian Stauffer

 

Encourage young boys and girls to run, jump, squeal, hop and chase after each other or after erratically kicked balls, and you substantially improve their ability to think, according to the most ambitious study ever conducted of physical activity and cognitive performance in children. The results underscore, yet again, the importance of physical activity for children’s brain health and development, especially in terms of the particular thinking skills that most affect academic performance.

The news that children think better if they move is hardly new. Recent studies have shown that children’s scores on math and reading tests rise if they go for a walk beforehand, even if the children are overweight and unfit. Other studies have found correlations between children’s aerobic fitness and their brain structure, with areas of the brain devoted to thinking and learning being generally larger among youngsters who are more fit.

But these studies were short-term or associational, meaning that they could not tease out whether fitness had actually changed the children’s’ brains or if children with well-developed brains just liked exercise.

So for the new study, which was published in September in Pediatrics, researchers at the University of Illinois at Urbana-Champaign approached school administrators at public elementary schools in the surrounding communities and asked if they could recruit the school’s 8- and 9-year-old students for an after-school exercise program.

This group was of particular interest to the researchers because previous studies had determined that at that age, children typically experience a leap in their brain’s so-called executive functioning, which is the ability to impose order on your thinking. Executive functions help to control mental multitasking, maintain concentration, and inhibit inappropriate responses to mental stimuli.

Children whose executive functions are stunted tend to have academic problems in school, while children with well-developed executive functions usually do well.

The researchers wondered whether regular exercise would improve children’s executive-function skills, providing a boost to their normal mental development.

They received commitments from 220 local youngsters and brought all of them to the university for a series of tests to measure their aerobic fitness and current executive functioning.

The researchers then divided the group in half, with 110 of the children joining a wait list for the after-school program, meaning that they would continue with their normal lives and serve as a control group.

The other 110 boys and girls began being bused every afternoon to the university campus, where they participated in organized, structured bouts of what amounted to wild, childish fun.

“We wanted them to play,” said Charles Hillman, a professor of kinesiology and community health at the University of Illinois who led the study.

Wearing heart rate monitors and pedometers for monitoring purposes, the children were guided through exercise that doubled as romping. The activities, which changed frequently, consisted of games like tag, as well as instruction in technique skills, such as how to dribble a soccer ball. The exercise curriculum was designed to improve both aerobic endurance and basic motor skills, Dr. Hillman said.

Each two-hour session also included downtime, since children naturally career about and then collapse, before repeating the process. In total, the boys and girls generally moved at a moderate or vigorous intensity for about 70 minutes and covered more than two miles per session, according to their pedometers.

The program lasted for a full school year, with sessions available every day after school for nine months, although not every child attended every session.

At the end of the program, both groups returned to the university to repeat the physical and cognitive tests.

As would have been expected, the children in the exercise group were now more physically fit than they had been before, while children in the control group were not. The active children also had lost body fat, although changes in weight and body composition were not the focus of this study.

More important, the children in the exercise group also displayed substantial improvements in their scores on each of the computer-based tests of executive function. They were better at “attentional inhibition,” which is the ability to block out irrelevant information and concentrate on the task at hand, than they had been at the start of the program, and had heightened abilities to toggle between cognitive tasks.

Tellingly, the children who had attended the most exercise sessions showed the greatest improvements in their cognitive scores.

Meanwhile, the children in the control group also raised their test scores, but to a much smaller extent. In effect, both groups’ brains were developing, but the process was more rapid and expansive in the children who ran and played.

“The message is, get kids to be physically active” for the sake of their brains, as well as their health, Dr. Hillman said. After-school programs like the one he and his colleagues developed require little additional equipment or expense for most schools, he said, although a qualified physical education instructor should be involved, he added.

Extended physical education classes during school hours could also ensure that children engage in sufficient physical activity for brain health, of course. But school districts nationwide are shortening or eliminating P.E. programs for budgetary and other reasons, a practice that is likely “shortsighted,” Dr. Hillman said. If you want young students to do well in reading and math, make sure that they also move.

Fitness May Boost Kids’ Brainpower

Healthday.com

Study found fitter kids had different white matter, which helps brain regions communicate with each other

Fitness May Boost Kids' Brainpower

By Randy Dotinga
HealthDay Reporter

TUESDAY, Aug. 19, 2014 (HealthDay News) — Exercise and brainpower in children may not seem closely related, but a small new study hints that fitness may supercharge kids’ minds.

The finding doesn’t prove that fitness actually makes children smarter, but it provides support for the idea, the researchers said.

“Our work suggests that aerobically fit and physically fit children have improved brain health and superior cognitive [thinking] skills than their less-fit peers,” said study author Laura Chaddock-Heyman, a postdoctoral researcher with the department of psychology at the University of Illinois at Urbana-Champaign. “Hopefully, these findings will reinforce the importance of aerobic fitness during development and lead to additional physical activity opportunities in and out of the school environment.”

The researchers launched their study to gain more insight into the connections between fitness and the brain in children. Other research has connected higher levels of fitness to better attention, memory and academic skills, Chaddock-Heyman said.

And two recent studies found that fit kids are more likely to have better language skills and to do better on standardized tests for math and reading.

But there are still mysteries. While moderate exercise boosts brainpower for a few hours — making it a good idea to work out before a test — it’s not clear how fitness affects the brain in the long term, said Bonita Marks, director of the Exercise Science Teaching Lab at the University of North Carolina at Chapel Hill. “The chronic impact is less certain and, for health, really the key for future research and health management,” she added.

The new study didn’t examine any thinking skills, but instead looked only at the brain’s “white matter,” which helps different brain regions communicate with each other. The researchers scanned the brains of 24 kids aged 9 and 10, and found that white matter was different in the fitter kids, potentially a sign of better-connected brains.

Higher levels of fitness may boost blood flow, increase the size of certain brain areas and improve the structure of white matter, Chaddock-Heyman said.

What do the findings mean in the big picture?

It’s hard to know for sure. Megan Herting, a postdoctoral fellow with the division of research on Children, Youth, and Families at Children’s Hospital of Los Angeles, pointed out that the kids with lower fitness levels also weighed more, “so it is unclear if it is actually fitness or ‘fatness’ that may be affecting the brain. “Studies show that individuals with obesity have different brains compared to their healthier-weight peers,” she said.

As for the stereotype of the 99-pound weakling nerd, Herting suggested it may be time for a rethink. “These findings do challenge that if you are aerobically fit, you are likely to be dumb. In fact, from an evolutionary perspective, we were made to move. So rather than fitness being ‘good’ for the brain and cognition, it is feasible that being sedentary may be ‘bad.'”

The researchers are now working on a study that assigns some kids to take part in exercise programs to see what happens to their brains over time when compared to other kids, Chaddock-Heyman said.

The study appears in the August issue of the journal Frontiers in Human Neuroscience.

More information

For more about fitness, try healthychildren.org.

SOURCES: Laura Chaddock-Heyman, Ph.D., postdoctoral researcher, department of psychology, University of Illinois at Urbana-Champaign; Bonita Marks, Ph.D., professor, exercise physiology, and director, Exercise Science Teaching Lab, department of exercise and sport science, University of North Carolina at Chapel Hill; Megan Herting, Ph.D., postdoctoral fellow, division of research on children, youth and families, Children’s Hospital of Los Angeles; August 2014 Frontiers in Human Neuroscience

The Overlooked Secret to Great Performance

The New York Times

BY TONY SCHWARTZ
Ignore exercise, and you will get progressively weaker, and more vulnerable to illness.Matthew Peyton for The New York TimesIgnore exercise, and you will get progressively weaker, and more vulnerable to illness.

Think of a time when you were performing at your best and another occasion when you were performing at your worst. Now, take a few moments to visualize the two occasions in your mind.

The vast difference between these two experiences has nothing to do with your inborn talent or your skills. How much of your capacity you bring to work on any given day depends, to a large degree, on how much energy you’ve got in your tank.

Obvious as that seems, we underestimate how much impact taking care of ourselves — and feeling taken care of — has on our performance.  Unlike machines, which run on a single source of energy, human beings require four types of fuel to perform at their best: physical, emotional, mental and spiritual. Each of these influences one another, and none is sufficient by itself.

Physical energy is the core fuel we require to get things done. Everything we do rests on that foundation, and how we feel is influenced by what we eat and when, how much we exercise, whether or not we renew our energy intermittently through the day and how many hours we sleep.

Go without eating for five or six hours, for example, and you’re depriving the brain of its ravenous need for glucose. Work continuously for multiple hours without a break, and you’re progressively depleting your capacity to remain calm and collected under pressure. Ignore exercise, and you will get progressively weaker, and more vulnerable to illness.

No single behavior in our lives matters more than sleep, because without enough of it — a minimum of seven to eight hours for 97 percent of us — the toll shows up in every aspect of our lives. Even small amounts of sleep deprivation take a toll, for example, on vigilance on a task, our mental agility on tasks, our mood and even our motivation.

The second fuel in our lives is emotional. We assume we’re rational beings, but it turns out we’re run largely by our emotions, for better and for worse. Think again about how you feel when you’re performing at your best. We’ve asked this question to tens of thousands of people over the years and the adjectives people describe are always the same: energized, excited, happy, positive, engaged and in the flow.

Put simply, we perform best when we’re feeling high positive emotions, and we perform less well as our feelings move in the direction of anger, frustration, impatience and fear — all of which are also draining, and antagonizing to others. Just being aware that negative emotions undermine us can be a powerful impetus to address them.

Psychologists like Roy Baumeister have long written about our “negativity bias” — the default inclination to focus more on what is wrong in our lives than what’s right. While we’re wired to be vigilant to threat, it’s also possible to consciously cultivate positive emotions.

Taking time to appreciate one’s bounty and express gratitude all serve this end. So, too, does spending time with people we care about deeply, which helps explain why having a close friend at work has a powerful and positive impact on engagement and performance at work.

The mental fuel we require to perform at our best is focus, and more so than ever in a world of infinite distractions. Control of our attention — the capacity to put our focus where we want it to be — makes it possible not just to get the right work done, but also to intentionally shape our experience. Attention, like any other muscle, gets stronger when we train it — which helps explain why practices like mindfulness are suddenly generating so much interest in organizations

The fourth fuel that influences our performance is the sense of purpose we bring to our work. Is there any doubt that we feel more positive — and bring more passion and focus to what we do — when we believe what we’re doing really matters? Paradoxically, the more we invest in adding value to others, the better we feel about ourselves.

Just as we underestimate how much these sources of fuel influence our performance, so do the organizations for which we work. Few companies or leaders I’ve encountered systematically focus on, and invest in, how their employees feel, even though doing so would serve their bottom line.

The 2012 Global Workforce Study conducted by the consulting firm Towers Watson measured the relationship between engagement — the willingness of employees to invest discretionary effort at work — and financial results. The key for the most highly engaged employees turned out to be their ability to maintain their energy and enthusiasm at work.

The differentiating factor among companies with the most highly engaged employees was an environment that supported people’s physical, emotional and social well-being. Companies that did this least well had an average operating margin of 10 percent. Companies that best supported employees had an average operating margin of 27 percent.

It’s a dual challenge. Organizations stand to improve performance by helping their employees feel better every day. We perform better and more sustainably when we take better care of ourselves.

Exercise May Protect Children From Stress

NY Times Article

By JAN HOFFMAN
Hélène Desplechi/Getty Images

Physically active children generally report happier moods and fewer symptoms of depression than children who are less active. Now researchers may have found a reason: by one measure, exercise seems to help children cope with stress.

Finnish researchers had 258 children wear accelerometers on their wrists for at least four days that registered the quality and quantity of their physical activity. Their parents used cotton swabs to take saliva samples at various times throughout a single day, which the researchers used to assess levels of cortisol, a hormone typically induced by physical or mental stress.

There was no difference in the cortisol levels at home between children who were active and those who were less active. But when the researchers gave the children a standard psychosocial stress test at a clinic involving arithmetic and storytelling challenges, they found that those who had not engaged in physical activity had raised cortisol levels. The children who had moderate or vigorous physical activity showed relatively no rise in cortisol levels.

Those results indicate a more positive physiological response to stress by children who were more active, the researchers said in a study that was published this week in The Journal of Clinical Endocrinology and Metabolism. The children who were least active had the highest levels.

“This study shows that children who are more active throughout their day have a better hormonal response to an acute stressful situation,” said Disa Hatfield, an assistant professor of kinesiology at the University of Rhode Island, who was not involved in the study.

Dr. Hatfield noted that the study did not control for sugar intake, which has also been associated with higher levels of cortisol. And as the researchers themselves noted, the wrist-born accelerometers could not accurately measure certain activities like bicycling or swimming.

Michael F. Bergeron, a professor of pediatrics at the University of South Dakota and executive director of the National Youth Sports Health and Safety Institute, cautioned that chronic levels of cortisol might be a better measurement of a child’s propensity toward stress, rather than the single-day measurements taken in the new study.

“A single response to a single stressor may be what the body needs to do, and that’s not necessarily a bad thing,” he said.

Although elementary schools in the last decade have generally been supportive of physical education, only 29 percent of high school students meet the national guideline of 60 minutes a day, said Russell R. Pate, a professor of exercise science at the University of South Carolina, who has worked on national studies of fitness levels in students.

“It’s not a huge surprise that kids who are encouraged to be more active would be more relaxed,” he said.

In a school, a child who gets more activity on a daily basis, Dr. Hatfield said, will respond better to everyday stressors like tests and social challenges. “The study suggests the physiological reason: it may be because their hormonal response is different,” she said.