Once, I was at my son's school during recess and noticed that (other than a few exceptions) it was mostly boys playing kickball and girls sitting in small groups around the jungle gym chatting and playing cats cradle. At the time, I didn't think much of it, but I was reminded of it the day when I read an article about how young and old females aren't as active as males.

Researchers from Liverpool John Moores University followed 10 and 11-year-old children during recess and found that boys tend to engage in more active play than girls. On the flip side of the coin, another study found that women over age 70 are less likely to be active than men.

It's important for everyone to be active. But it's certainly important for girls (during the formative years when their bones are growing) and older women (who need to maintain bone density) to be physically active.