looking at full joint replacement (one a knee, the other a hip) within the year...both are in their mid-40's.

My sister is a marathoner, and she's had multiple stress fractures in her feet and legs over the years. She's looking at full knee replacement before she's even 40.

Obviously, running is a great way to stay in shape. Like anything else, though, it should be done in moderation. There comes a point where the health benefits of running are outweighed by the injuries you sustain by doing it constantly.