Worried about your knees? Running may actually help them, not harm them.

Photo: TimTak, Flickr

Yep, despite years of believing that pounding the pavement on regular jogs was the worst thing you could do for your poor knees, it turns out that running won't cause arthritis, and in fact will actually make them stronger.

That said, this only goes for runners with healthy, injury-free knees -- if you've injured yours in the past, be sure to consult your doctor to find out if running is the right exercise for you. If it's not? Don't despair -- there are plenty of other activities that will get your blood pumping just as effectively.