This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. With the aging of the United States population, osteoporosis has become a major public health concern; an estimated 25 million Americans have osteoporosis. This disorder is more common among women than among men for at least three reasons: (1) women have lower peak bone mass than men; (2) women lose bone mass at an accelerated rate after menopause when estrogen levels decline; and (3) women have a longer life span than men. Until recently, efforts to curtail the impact of osteoporosis on the population have been primarily focused on ameliorating bone loss among the elderly through promoting estrogen supplementation and increased calcium intake for post-menopausal women. In the last decade the literature has grown with studies examining physical exercise programs to reduce the rate of decline in muscular strength and bone mass with progressive aging. While this type of evidence lends support to the idea that increased physical activity will lead to higher bone mass density (BMD) among post-menopausal women, it has yet to be generalized to pre-menopausal women who still have the opportunity to increase their peak bone mass. It is the goal of this research to implement a physical activity program of high-impact (HI; step aerobics) and high-tension (HT; resistance training) loading of the musculoskeletal system for nine (9) months (3 sessions per week) specifically designed to influence bone mineralization and the integrity of long bones. Bone mass peaks between the second to third decade of life. Therefore it has been suggested that the risk of osteoporosis may be attenuated by optimizing bone mineralization during adulthood. The evidence indicated that this goal may be achieved by ensuring that adult females ingest sufficient calcium and engage in regular vigorous physical activity. These two behaviors interact such that the beneficial effects of calcium will only be realized in the presence of adequate physical activity. Unfortunately, only about one-quarter of young adults (age 20-35) regularly participate in vigorous physical activity. Participation in all types of activity declines strongly with age and females, who are at greater risk for osteoporosis, are less likely to be regularly active than males. Thus, pre-menopausal females represent a high-risk group for failing to achieve optimal peak bone mass and stand to benefit greatly from the effects of increased physical activity. The case in support of physical activity as a means of supporting bone development has been built primarily on cross-sectional and retrospective data indicating that individuals who engage in greater levels of physical activity tend to have higher bone density as compared to sedentary individuals. Additional research has shown that increasing levels of physical activity may attenuate decreases in bone density associated to osteoporosis among post-menopausal women. While suggestive of the beneficial role that increased physical activity may play among sedentary females, the data have not demonstrated that previously sedentary females who begin a program of high-impact (HI) and high-tension (HT) physical activity will, in fact, decrease their risk of osteoporosis by increasing bone density and bone strength. Research in the area of exercise intervention on BMD or bone bending stiffness in pre-menopausal sedentary females after the critical period of peak bone mass formation is scarce. California State Polytechnic University, Pomona (CSPUP) has applied for a special grant from the NIH minority biomedical research section (Support of Continuous Research Excellence or 'SCORE'). As outlined below, this project involves two components: (1) exercise training and (2) physiological and behavioral evaluation. The subject selection, exercise training, and most physiological measurements will be conducted at CSPUP while the University of California, Irvine (UCI) satellite General Clinical Research Center (GCRC) will be responsible for measuring bone properties and body composition. A typical subject will be selected, enrolled for approximately 13 months, receive exercise training (9 months; 3 sessions per week), and undergo physiological measurements at CSPUP. The UCI GCRC will conduct bone property evaluations and body composition assessments at baseline, mid-point of intervention, conclusion of intervention, and approximately four (4) months following conclusion of intervention. The primary objective of this proposal is to investigate the long-term effect of regular exercise with high-impact and high-tension loading of the musculoskeletal system on bone health among pre-menopausal women. The study will focus on sedentary young adult females, a growing population and one at particularly high risk for developing osteoporosis later in life. We will test the hypotheses that the intervention will lead to measurable increase in bone strength and bone mineral density of a nine-month period of observation. The primary specific aim is to examine the effects of two different modes of musculoskeletal loading that provide high-impact and high muscle tension, respectively on bone bending stiffness and bone mineral density (BMD) among sedentary pre-menopausal 20-35 year old women. The secondary specific aims are: 1. To compare the effect of HI and HT on loaded limbs and markers of bone turnover and/or formation in the blood and urine among sedentary pre-menopausal 20-35 year old women. 2. To determine if changes in muscular endurance and muscular strength, are predictors of changes in bone bending stiffness, BMD, markers of bone turnover and/or formation in the blood and urine among sedentary pre-menopausal 20-35 year old women. 3. To determine the effects of HI and HT on strength, muscular endurance, and cardiorespiratory endurance among sedentary pre-menopausal 20-35 year old women. Hypothesis 1: HI and HT loading of the lower extremities will induce site specific increase in tibia bending stiffness and BMD of the lower limbs that are not observed in the control condition, whereas bending stiffness and BMD of the unloaded ulna will be unchanged in all conditions. Hypothesis 2: HI and HT loading will induce positive changes in bone turnover and/or biochemical markers of bone formation and resorption while the control group will experience no changes in these measures.
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