(The Atlantic) - Mothers today may feel like they’re too busy to sit down, and many probably are, but a new report suggests that on average they are far more sedentary than moms were 50 years ago.

Since 1965, women with children have logged increasingly more time watching television and driving, and increasingly less time playing with children, doing chores, and exercising, according to a new report published this week in the journal Mayo Clinic Proceedings.

In 1965, mothers of children aged 5 to 18 spent 14.2 more hours a week being physically active than being sedentary. In 2010, they spent 3.8 more hours a week being sedentary than they did on physical activity.

The report authors used the American Heritage Time Use Study, which tracks time-use data for a nationally representative sample of people over the past five decades.* For the purposes of the report, “physical activity” was defined as time spent cooking and cleaning, along with playing with children and exercising. Sedentary activity was everything else non-work-related, so time spent in front of tablets, televisions, and computers, as well as time spent driving.

They found that mothers with older children (ages 5-18) were physically active for about 11 hours per week less in 2010 than in 1965. Among moms with children younger than 5, the decline was nearly 14 hours a week. Today, the two groups are physically active for 20.9 and 29.7 hours each week, respectively.

Though unemployed mothers might be thought of as having more time for exercise, physical activity has decreased more among mothers who don't work than among those who have full-time jobs. (Though moms who don’t work still spend more total time being physically active than those who do).

Mothers with older children have also increased their sedentary time by 7 hours a week since 1965. The increase was 5.7 hours a week for mothers with younger children. Again, unemployed mothers saw greater increases in sedentary time. As a result, mothers today burn between 1,238 and 5,835 calories less each week than mothers did in the 1960s. A pound of fat is roughly 3,500 calories.

Of course, much of the decline has to do with housework. Dishwashers didn’t become a staple of middle-class homes until the 1970s, and clothes washers and dryers were out of reach for many until the 1980s. Few women today would likely say that their preferred form of exercise is scrubbing shirts on a washboard.

But the other side of the technological-advancement argument is the ubiquity of screen-based entertainment: Physical activity time reached a “nadir” in the 1990s, according to the report authors, just as the Internet became popular and TVs plummeted in price.