oh, them bones.  and their decreasing strength and density as we age.  even the ancient chinese doctors, without the use of x-rays or other modern imaging techniques, recognized that bone strength fades as we age.  bones mirror our physical and energetic Shen ("kidney") system, or our reproductive physiology, in that they peak in strength in our mid-twenties, and then decline with age.from the Huang Di Nei Jing, the 2000 year old "textbook" which is the foundation of modern TCM theory:"in general, the reproductive physiology of woman is such that at seven years of age her kidney energy becomes full, her permanent teeth come in, and her hair grows long.  At fourteen years the tian kui, or fertility essence, matures, then ren / conception and chong / vital channels responsible for conception open, menstruation begins, and conception is possible.  At twenty-one years the kidney energy is strong and healthy, the wisdom teeth appear, and the body is vital and flourishing.  At twenty eight years the bones and tendons are well developed and the secondary sex characteristics are complete.  This is the height of female development.  At thirty-five years the yang-ming / stomach and large intestine channels that govern the major facial muscles begin to deplete, the muscles begin to atrophy, facial wrinkles appear, and the hair begins to thin.  At forty-two all three yang channels  taiyang, shaoyang, and yangming - are exhausted, the entire face is wrinkled, and the hair begins to turn gray.  At forty-nine years the ren and chong channels are completely empty, and the tien kui has dried up.  hence, the flow of the menses are ceased and the woman is no longer able to conceive...  When the energy of all the organs is full, the excess energy stored in the kidney is excreted for the purposes of conception.  But now, the organs have aged and their energes have become depleted, the bones have become frail and stiff, and movements are hampered.  The kidney reservoir becomes empty, marking the end of the power of conception"  -From The Yellow Emperor's Classic of Medicine, Maoshing Ni, Shambhala Publications Inc., 1995, page 2.   http://www.amazon.ca/Yellow-Emperors-Classic-Medicine-Translation/dp/1570620806 The key, therefore, is to balance the energies in the whole of the body, as well as nourishing & strengthening the important Shen / kidney system, to maximize bone health and strength.