456 the Response of Trabecular Bone to Physical Activity in Young Sedentary Males

Abstract

1A B STR A C T Bone is a dynamic tissue that is continuously undergoing cycles of resorption and formation throughout life. Factors known to effect this remodelling process include an individual's nutritional and hormonal status and physical activity and achievable bone density is dependent on the interaction between an individuals chosen lifestyle and genetic make-up. There is considerable evidence that physical activity may have a positive effect on bone mineral density through the effects of mechanical loading and local and systemic physiological mechanisms. Lack of a change in bone mineral density following exercise has also been found, and this discrepancy in the literature may reflect differences in the nature, intensity and duration of the exercise programs that have been used. The complexity of the interaction between lifestyle and genetic factors, age and site specific responses also makes interpretation of the literature difficult. It has been suggested that attainment of a high peak bone mass earlier in life may compensate for the normal loss of bone which occurs and accelerates with aging. Moderate intensity activity has been shown to have a positive effect in the development of skeletal mass in children.However, there is a paucity of prospective information on the effects of physical activity in early-adulthood. The aim of this study was to investigate whether a protocol of running training designed to increase cardiovascular fitness would effect changes in bone mineral density (BMD), bone mineral content (BMC) and bone metabolism of young sedentary males. This study was also designed to assess possible associations between cardiovascular fitness and anthropometric variables and BMD and BMC.Twenty-six sedentary males with an average age of 22.2 years volunteered to participate in this study. Sixteen of those chosen to participate undertook a 16 week program of progressive running training and as the exercise program progressed the running distance became longer and the intensity of the runs was increased. Ten males acted as the control group and did not participate in any organised program of physical activity. Physical activity diaries were kept by all experimental and control subjects in order to assess daily training histories of both formal and informal activity. A maximal exercise treadmill test 11 was conducted to assess the cardiovascular fitness of all subjects and establish the training intensities for the exercising subjects. Tests were conducted before commencement of the program, at 4 weekly intervals and immediately following the intervention period. Cumulative heart rates and time to exhaustion from the initial and final maximal treadmill test were used as indicators of a change in cardiovascular fitness over the 16 weeks. Bone mineral density and content was assessed at three sites on the proximal femur and in lumbar vertebrae 2 to 4 using dual energy x-ray absorptiometry . The biochemical markers of bone formation and resorption, namely serum osteocalcin and urinary hydroxyproline we...