When biomedical student Seth Donahue ran into a black bear while hiking in California’s Sierra Nevada Mountains, he felt inspired rather than frightened.  He wondered how the Ursus americanus, which hibernates for up to seven months a year, can wake with bones that are just as strong as they were when it first settled down for a snooze.  Taking a long nap might sound like a great plan, but if a human were to do the same for only two weeks, its bones would begin to wear down from disuse.

Throughout our lifetimes, our bones are constantly being rebuilt.  Over time, we lose more bone than we replace.  As a result, many elderly people suffer from osteoporosis, the significant bone loss that can increase the risk of fracture.  This disease affects more than 10 million Americans and is the underlying cause behind 1.5 million fractures every year (Jennings

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