From Atlantic Cities:

More than one-third of adults in the U.S. have not walked for more than 10 minutes straight over the course of the last week. People typically walk about 3 miles per hour, so a 10-minute walk covers just about half a mile. That’s like walking two-and-a-half laps around a football field, or walking halfway across the Brooklyn Bridge, or walking about four average city blocks and then turning around and walking back. All this is to say that 10 minutes of walking isn’t that much. And still, about 38 percent of the adult U.S. population can’t even manage to do it just once in a week.

At least they couldn’t in 2010, which is the latest data available and is the basis of a new report out from the Centers for Disease Control and Prevention. But if 38 percent of adults sounds like a lot, comfort yourself by looking back at the numbers from 2005. Back then, more than 44 percent of adults didn’t walk more than 10 minutes at a time.

The opposite side of these findings is, of course, that more people were walking in 2010 than were in 2005. Sixty-two percent of adults were walking those 10 minutes in 2010, compared with more than 55 percent in 2005.

Toward public health aims, this is a positive change. The 2008 Physical Activity Guidelines for Americans recommends at least 150 minutes of moderate-intensity aerobic physical activity per week. Walking fits that bill. And though a 10-minute walk is embarrassingly shy of 150 minutes, it’s a good step. And it’s an indicator. According to the CDC, those who met the 10-minute walk mark were about three times more likely than non-walkers to meet the 150-minute activity guideline. (Granted, using the standard of a single 10-minute walk over the course of seven days to separate “walkers” from “non-walkers” is a pretty low threshold to surpass.) And more people are meeting that 150-minute mark: 48 percent of adults met the guideline in 2010 compared to 42.1 percent in 2005.

But even while more adults are walking, the total amount they’re walking seems to be falling. According to the report, the average time walkers spent walking dropped from about 15 minutes a day in 2005 to about 13 minutes a day in 2010.

So we’re walking more but still walking less.

The CDC isn’t sure why this is happening, but one possible explanation could be that the reasons for walking are changing. It may also be that more types of people are walking, not just the relatively health conscious that are heading out for a daily walk, but also people who maybe aren’t specifically walking for exercise. It could also be that more people are walking but for less time because they’re walking to the store or to the coffee shop rather than walking as a regimented exercise session of a mile or two per day. Whatever the reason, it will be interesting to see whether these trends continue.