Writing for the New York Times, Kim Tingley explores how step-counting became such an exercise fad, whether it's truly an effective way to measure physical activity—and how many daily steps you really need to take to gain health benefits.

Cheat sheet: Wearables 101

How everyone became obsessed with measuring low-intensity activity

Since the 1960s, physicians have argued that exercise, which once was believed to be hazardous to the health of middle-aged people, can actually lower the risk of mortality. But early studies examining the link between exercise and health were hampered by the technology of the era.

At the time, Tingley writes, "The only way researchers could learn about [physical activity] was by asking people to describe their behavior." As such, the questions researchers asked tended to focus on high-intensity bouts of physical activity, such as jogging and bicycling. In other words, things that could be examined in a lab.

"We never asked about light-intensity physical activity, because we realized it's poorly reported," said I-Min Lee, a professor of medicine at Harvard Medical School. "Putzing around your house, picking up after yourself, doing a little bit of light gardening—how well do people remember that?"

Soon, researchers had "ample evidence that the more 'moderate' to 'vigorous' activity people reported doing, like brisk walking or raking leaves, the lower their risk of diabetes, certain cancers and cardiovascular disease," Tingley writes. But they had little to say about whether lighter-intensity activity, such as walking, also carried health benefits.

Still, over the years, studies uncovered tantalizing "hints" that low-intensity activity could have a significant impact on health, Tingey writes—such as by finding a link between long periods of sitting and poor health.

The stage was set for an explosion of interest in low-intensity activity, if only there were a way to measure it.

Enter the step counter

Into that void entered the iPhone, the iPhone, and other lightweight fitness trackers, which began hitting U.S. markets a decade ago.

Suddenly, people had a way to measure their low-intensity activity over the course of a day—and a public health fad was born.

The first widely embraced step-counting goal, 10,000 steps a day, was not especially evidence-backed. In fact, Tingley reports, it came from the Japanese term used for early step counters, "manpo-kei, which translates to '10,000 steps meter'—a number apparently chosen in part because the Japanese character for it looks like a walking man." But once step counters became widely available, researchers were able to confirm that higher step counts were linked to better health.

For instance, a study published in JAMA Internal Medicine in May, for which Lee was the lead author, gave wearable devices to more than 16,000 older women as they went about daily activities for seven days, then observed the women's health and longevity four years later.

Lee found that participants who walked about 4,400 steps per day on average had a 40% reduced risk of mortality compared with the "least active" women, who averaged 2,700 steps per day. (The health benefits "maxed out," the researchers found, at around 7,500 steps per day.)

But it's important to note, researchers say, that all of this focus on step-counting is essentially a byproduct of the technology that happens to be available. "There's no evidence that steps are better for health than other kinds of light-intensity activity," Tingley writes, adding "[T]hey just happen to be a movement people make often that is also detectable."

In other words, we count steps not because it's necessarily the best way to measure low-intensity physical activity, but because it's an objective measurement that's easily gathered by low-cost technology.

Will other low-intensity physical activities ever be measurable?

While step counters gave researchers a pathway to measuring low-intensity physical activity, many details remain out of reach, Tingley writes.

For instance, a step counter can't determine how hard someone had to work to achieve a given step. Did the person walk or run? Were they carrying heavy groceries or picking up a toddler? All of these variables affect the physical intensity of walking and thus, potentially, the health benefits.

Further, many low-intensity activities, such as swiveling in an office chair or fidgeting while on your computer, aren't captured by step counters but may have important health benefits. And step counters also fail to capture many higher-intensity activities, such as weightlifting, that aren't associated with walking or running.

As, Kathleen Janz, a professor of health and human physiology at the University of Iowa, noted, we "don't have an app" that measures how much strength we use in a given day—but that doesn't mean that difficult-to-measure forms of physical activity are any less beneficial than steps (Tingley, New York Times, 8/21).