There is a great deal of documentation regarding the use of weight-bearing exercises to strengthen bones and help to head-off osteoporosis. Yoga requires you to lift your own body weight in many of its positions. Arm bone strength is helped with some poses such as upward and downward facing dog. Arm bones are particularly susceptible to fractures from osteoporosis. It was stated in a study, performed in Los Angeles at the California State University, that the bone density within the vertebral was increased with yoga practice. Because yoga has the ability to keep the stress hormone, cortisol, at lower levels, it is believed that this may help calcium to remain in the bones.