 Exercise training is effective for increasing bone mineral density and preventing osteoporosis, but the effects are small. When estrogen replacement is given to post-menopausal women the effectiveness of exercise training for improving bone mineral density is increased. Currently many women are concerned about the risks of taking hormone-replacement therapy and are seeking alternative therapies. The purpose of our study therefore is to use an estrogen-like dietary supplement derived from soy called a phytoestrogen soy isoflavone combined with exercise training for improving bone mineral density. 