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

CreditCreditJeenah Moon for The New York Times

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 lifespans 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 exercises, 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.”