Credit...Keith E. Morrison for The New York Times

For anyone interested in the relationship between exercise and living longer, one of the most pressing questions is how much we really need to stay healthy. Is 30 minutes a day enough? Can we get by with less? Do we have to exercise all in one session, or can we spread it throughout the day? And when we’re talking about exercise, does it have to be hard to count?

For years, exercise scientists tried to quantify the ideal “dose” of exercise for most people. They finally reached a broad consensus in 2008 with the Physical Activity Guidelines for Americans, which were updated in 2018 after an extensive review of the available science about movement, sitting and health. In both versions, the guidelines advised anyone who was physically able to accumulate 150 minutes of moderate exercise every week, and half as much if it is intense.

But what’s the best way to space out those weekly minutes? And what does “moderate” mean? Here’s what some of the leading researchers in exercise science had to say about step counts, stairwells, weekend warriors, greater longevity and why the healthiest step we can take is the one that gets us off the couch.

Aim for the 150-minute sweet spot.
“For longevity, 150 minutes a week of moderate to vigorous intensity physical activity clearly is enough,” said Dr. I-Min Lee, a professor of epidemiology at the Harvard T.H. Chan School of Public Health. She has extensively studied movement and health and helped draft the current national physical activity guidelines.

For practical purposes, exercise scientists often recommend breaking that 150 minutes into 30-minute sessions of speedy walking or a similar activity five times a week. “It is quite clear from numerous large-scale, well-conducted epidemiological studies that 30 minutes of moderate-intensity activity most days lowers the risk of premature death and many diseases, such as stroke, heart attack, Type 2 diabetes and many types of cancer,” said Ulf Ekelund, a professor specializing in physical activity epidemiology at the Norwegian School of Sports Sciences in Oslo, who has led many of those studies.

Moderate exercise, he continued, means “activities that increase your breathing and heart rate, so the exertion feels like a five or six on a scale between one and 10.” In other words, pick up the pace a bit if your inclination is to stroll, but do not feel compelled to sprint.

Consider exercise snacks.
You also can break up your exercise into even smaller segments. “It doesn’t matter whether exercise is done in a long, continuous 30-minute session or is dispersed across the day in shorter sessions,” said Emmanuel Stamatakis, an exercise scientist at the University of Sydney in Australia who studies physical activity and health.

Recent studies overwhelmingly show that we can accumulate our 150 weekly minutes of moderate exercise in whatever way works best for us, he said. “Many people may find it easier and more sustainable to squeeze in a few dozen one-minute or two-minute walks between work tasks” or other commitments. “There is no special magic to a sustained 30-minute session of exercise” for most health benefits.

Think of these bite-size workouts as exercise snacks, he said. “Activities like bursts of very fast walking, stair climbing and carrying shopping bags provide excellent opportunities for movement snacks.” To concentrate the health benefits of these workout nuggets, he added, keep the intensity relatively high, so you feel somewhat winded.

Conceivably, you also could cram all of your exercise into long Saturday and Sunday workouts. In a 2017 study by Dr. Stamatakis and colleagues, people who reported exercising almost entirely on weekends were less likely to die prematurely than those who said they rarely exercised at all. But being a weekend warrior has drawbacks. “It is certainly not ideal to spend the workweek totally sedentary and then try to compensate” over the weekend, Dr. Stamatakis said. You miss many of the health benefits of regular exercise, such as improved blood-sugar control and better moods, on the days you do not work out, he said. You also increase your risk of exercise-related injuries.

Count your steps.
The exercise recommendations remain the same if you measure your exercise in steps instead of minutes. For most people, “150 minutes of exercise a week would translate into about 7,000 to 8,000 steps a day,” Dr. Lee said. In a large-scale new study by Dr. Lee and Dr. Ekelund of the relationship between steps and longevity, published in March in The Lancet, the optimal step count for people younger than 60 was about 8,000 to 10,000 a day, and for those 60 and over, it was about 6,000 to 8,000 a day.

Consider more.
Of course, these recommendations about steps and minutes focus on health and life spans, not physical performance. “If you want to run a marathon or a 10K race as fast as possible, you need much more exercise,” Dr. Ekelund said.

The recommended 150 minutes a week also may be too little to stave off weight gain with age. In a 2010 study of almost 35,000 women that was spearheaded by Dr. Lee, only those who walked or otherwise exercised moderately for about an hour a day during middle age maintained their weight as they became older.

So, if you have the time and inclination, move more than 30 minutes a day, Dr. Lee and the other scientists said. In general, according to her research and other studies, the more active we are, well beyond 30 minutes a day, the more our risks of chronic diseases drop and the longer our lives may be.

But any activity is better than none. “Every single minute counts,” Dr. Ekelund said. “Walking up the stairs has health benefits, even if it only lasts for one or two minutes, if you repeat it regularly.”

Gretchen Reynolds will be taking time off from the PhysEd column to work on a book. In the meantime, follow her on Twitter (@gretchenreynold) or look for her on the running trails and bike paths.