Association between bone, body composition and strength in premenarcheal girls and postmenopausal women.

AIM: The study examined whether associations between bone, body composition and strength are age dependent. SUBJECTS AND METHODS: Two age levels (premenarcheal girls and postmenopausal women on HRT) were studied in a 10-month follow-up. Bone, lean and fat mass were measured by dual-energy X-ray absorptiometry (DXA), and strength was measured using an isokinetic dynamometer. RESULTS: In girls, significant correlations were found between mass (lean, fat and body mass), strength and most bone characteristics (r = 0.15-0.93). At the proximal femur changes in bone mineral density (BMD) were moderately related to changes in body composition. In the women, body mass and lean mass were significantly correlated with most bone characteristics (r = 0.34-0.82). Low to moderate correlations were observed between changes in bone and changes in body composition. After controlling for lean mass the relation between strength and bone was no longer significant. CONCLUSIONS: In premenarcheal girls, bone is partly determined by mass, with lean mass the most important predictor at the femoral sites. In postmenopausal women, lean mass is an important determinant of bone mineral content (BMC) and BMD, but changes in BMD are related to changes in fat. The relation between strength and BMD is mainly attributable to the relation between lean mass and BMD. The contributory effects of soft tissue to bone change over different life periods.

Influence of weight-bearing exercises on bone acquisition in prepubertal monozygotic female twins: a randomized controlled prospective study.

The aim of this study was to determine whether high-impact exercises have an osteogenic effect in 21 prepubertal female monozygotic twins aged 8.7 (SD 0.7) years. Bone mineral density (aBMD), bone mineral content (BMC), bone area, and body composition were derived from DXA. Skeletal maturity was assessed by the Tanner-Whitehouse technique. Anthropometric dimensions (28 dimensions) were measured and also used to derive adiposity and muscularity indices, and information about physical activity was obtained by questionnaire. These measurements were taken before and after the exercise period. The exercise program consisted of high-impact exercises. During 9 months, one girl of each twin pair performed the exercises 3 times a week under supervision of a teacher while their sisters served as control group. At baseline there were no differences between the groups. After 9 months, exercisers (Ex) and controls (Con) had similar increases in height and weight. Significant lower adiposity was observed in the exercise group vs the control group. None of the bone indices differed significantly between the two groups. When the analyses were done for a subgroup of twin pairs (n = 12) who did not participate in high-impact sports during their leisure time, significant differences were obtained for aBMD and BMC of the proximal femur in favor of the exercise group. These results indicate that for prepubertal girls who are not involved in sport activities or who are only involved in low-impact sport activities this exercise program has an osteogenic effect on the proximal femur, but for girls who are already involved in high-impact sports this protocol does not have any additional effect on the bone status.

Body composition estimations by BIA versus anthropometric equations in body builders and other power athletes.

BACKGROUND: Two main questions are stated: 1) are BIA and anthropometric equations accurate in estimating body composition in male power athletes and more specifically in body builders and 2) is there a difference in body composition when body builders are compared to weight and power lifters? EXPERIMENTAL DESIGN: this is a descriptive, comparative study on a selected sample of power athletes. PARTICIPANTS: 49 Belgian elite and sub-top male power athletes (34 body builders and 15 weight and power lifters) were included in this sample. More than 70% was in preparation of competition at time of data collection. MEASURES: an extended set of anthropometric measures was taken. Body composition was estimated by BIA (Bioelectrical Impedance Analysis) and by regression equations of skinfolds. Somatotype and muscle+bone areas were calculated. Factor analysis on all anthropometric measures was carried out to determine the body structure of the athletes. RESULTS: Compared to external visual criteria, the equations of Durnin and Womersley and Lohman (skinfolds) and the Guo-equation (BIA) were the only equations that could accurately estimate the body composition for this specific group of athletes. However, the sum of skinfolds attains the most accurate estimate of subcutaneous fatness. Body builders have significantly (p<0.01) larger arm and thigh circumferences and are more mesomorfic than the other power athletes (5.9 vs 3.8). CONCLUSIONS: This study shows that to estimate body composition in extreme power athletes BIA is not as accurate as compared to anthropometric equations. Moreover, the sum of a larger set of skinfolds is preferred to anthropometric prediction equations. In addition, body builders are more muscular and leaner than other power athletes.