ABSTRACT
Kaunas, Lithuania 17.1 INTRODUCTION The pubertal growth spurt accounts for about 20% of final adult height and 50% of adult peak bone mass (Wei and Gregory, 2009). Bone mass accrual during puberty is more dependable on sexual maturation than chronological age, and effects of sex hormones on the growing skeleton are associated with the osteoporosis later in life (Manolagas et al., 2002). One of the most effective osteoporosis prevention strategies may be maximising bone mineral content (BMC) during growing years by adopting weight-bearing physical activity in childhood and adolescence (French et al., 2000). High impact activities such as gymnastics, promote bone mineral accrual to a greater extent than low-impact activities such as swimming (Duncan et al., 2002). Bone mineral development in girls may be especially promoted by the increase of estrogen and insulin-like growth factor I (IGF-1) levels (MacKelvie et al., 2002). Several studies have investigated IGF-axis and sex hormone levels in relation with pubertal development and physical activity (van Coeverden et al., 2002). The positive association that exists between estradiol and bone turnover markers in early puberty disappears in late puberty and is also observed for IGF-1 (van Coeverden et al., 2002). Increasing sex hormones also increase IGF-1 levels that affect bone growth (Kanbur-Öksüz et al., 2004). The aim of this study was to determine the relationships of bone mineral density (BMD) and BMC at femoral neck and lumbar spine with IGF-1, IGF binding protein-3 (IGFBP-3) and sex hormones in pubertal female athletes. 17.2 METHODS The participants were 80 healthy adolescent girls aged 13-15 years. Athletic girls were rhythmic gymnasts (n = 23) and swimmers (n = 24) who have participated in their selected sports at least for the last two years. Control group (n = 33) consisted of the girls who took part only in compulsory physical education classes at school.
This study was approved by the Medical Ethics Committee of the University of Tartu (Estonia). BMD and BMC at femoral neck and lumbar spine were measured using DXA. Venous blood samples to determine the concentration of IGF-1, IGFBP-3 and estradiol were drawn after an overnight fasting at early follicular phase and analysed in duplicate on Immulite 2000 ( DPC, Los Angeles, CA, USA ). Statistical analysis was performed with SPSS 15.0 for Windows (USA). Means and standard deviations (±SD) were determined. A one-way analysis of variance (ANOVA) and Tukey post hoc test were used to establish the differences between the groups. Pearson’s product moment correlation was used to examine relationships between parameters. Partial correlation analysis was used to examine these relationships after controlling for age, body height, and body mass (Wang et al., 2004). The effect of IGF-1, IGFBP-3 and estradiol to the BMD and BMC was analysed by stepwise multiple regression analysis. The level of significance was conducted at p<0.05. 17.3 RESULTS Mean anthropometrical and bone parameters and blood concentrations of IGF-1, IGFBP-3 and estradiol are presented on Table 17.1. BMD values in femoral neck in rhythmic gymnasts group were higher compared with swimmers and controls. There were no significant differences between groups in measured hormones (see Table 17.1). After adjusting for age, body height, and body mass, the relationships between BMD variables, IGF-1, and IGF-1/IGFBP-3 remained significant (r=0.460.60; p<0.05) in rhythmic gymnasts group but not in swimmers or controls. BMD at femoral neck and lumbar spine were also related to estradiol levels (r=0.450.60; p<0.05) only in rhythmic gymnast group. Only BMC at femoral neck remained associated with IGF-1/IGFBP-3 molar ratio in rhythmic gymnasts group after adjusting for age, body height, and body mass.
