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When we were kids, we loved running and jumping. And recent research shows we should keep it up. The force from such high-impact activities actually sends a signal to your bone-building cells that it's time to get to work. In a 2014 study in the American Journal of Health Promotion, researchers measured the hipbone density of premenopausal women over the course of 16 weeks and found that those who twice daily jumped ten times with 30 seconds of rest between each jump showed significant gains in bone density compared with those who didn't jump at all. So get moving!