How to improve your mood, energy level, agility, cardiovascular system and bone density by doing this one simple thing.

FIT IN A MINUTE | Gretchen Rubin, author of The New York Times bestseller The Happiness Project, wrote a blog post last December on the joy of jumping up and down. Gretchen claims that the simple act of jumping up and down—in street wear, no special equipment or gym strip required—relaxes and/or invigorates her, depending on the situation. Oh yes, and it makes her kids laugh too, something that contributes to a more lighthearted mood at home. Read more