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Jump (slowly)
Exercise is regenerating to your muscles—and your bones—and one type of movement comes out a leap ahead. In a study in the American Journal of Health Promotion, premenopausal women who jumped 10 to 20 times twice a day improved their hip bone-mineral density after 16 weeks better than a control group. The catch? You need a 30-second rest in between each jump. That's because bone becomes desensitized with repeated stress, quickly acclimating to the motion of jumping continuously, says study co-author Larry Tucker, PhD. Bones then don't have the opportunity to rebuild and strengthen. Waiting the 30 seconds, however, doesn't allow bones to adapt to the stress from exercise, driving greater gains in bone mass.