I love simple solutions to complicated problems.

So thanks to the Scottish researchers who recently did a study comparing physical activity levels among teens who walk to school, versus those who rode a car, bus or train.

Obviously, the walkers were guaranteed to get a certain amount more exercise -- whatever it took for them to amble from home to school, lugging the obligatory 25 pounds of textbooks, plus whatever it takes to be cool in a Scottish high school. But that isn't what the researchers were after. They looked at how active the two groups of kids were during other times in their day -- morning break, lunchtime, and after school.

The kids, 13- and 14-year-olds from schools near Edinburgh, each had a device to record the time and distance of vertical movement throughout the day. The devices were worn all day except during bathing and swimming.

It turned out by every measure, the walkers were more active than the riders throughout the day. They got 8.9 percent more exercise during school hours, 4.2 percent more exercise during break, 18.4 percent more exercise during lunch, and 17 percent more exercise outside of school.

Of course, depending on your perspective, the results might seem a little unnerving -- whoever supervises the lunchroom might not be too thrilled to see an 18.4 percent increase in milling around, bread-roll tossing, jostling in line, etc.

But in general, it's heartening to know that getting off on the right foot in the morning can help a teen stay active all day.