ABSTRACT
School of Medicine, Tel-Aviv University, Israel; 2Pediatric Endocrine Unit, Kaplan Medical Center, Rehovot, Israel; 3Bar-Ilan University, Ramat Gan, Israel;
4Pediatric Exercise Research Center, Department of Pediatrics, University Children’s Hospital, University California, Irvine, California, USA
14.1 INTRODUCTION Extensive efforts are made in competitive sports to quantify objectively the fine balance between training intensity and athlete's tolerance. Recent reports suggest that exercise leads to a simultaneous increase of antagonistic mediators. Exercise stimulates anabolic components of the growth hormone (GH) IGF-I (insulinlike growth factor-I) axis (Eliakim et al., 2005), and elevates catabolic proinflammatory cytokines such as Interlukin-6 (IL-6), IL-1 and tumor necrosis factor-$ (TNF-$) as well (Nemet et al., 2002). It was suggested that evaluation of the exercise-induced changes in these circulating mediators can provide a new insight into quantification of training loads. The effect of a single exercise and/or exercise training on the GH-IGF-I axis and inflammatory cytokines was studied mainly in adults participating in individualized endurance-type sports. Only recently several studies examined the effect of supra-maximal anaerobic bout (Wingate anaerobic test) and sprint interval training on these mediators (Meckel et al., 2009, Stokes et al., 2005). Very few studies have examined the effect of training on the GH-IGF-I axis and inflammatory markers in children and adolescent elite athletes, and in team sports which are very popular in these age groups (Nemet et al., 2003). Moreover, gender-associated differences in the response of these circulating mediators to exercise training in elite athletes have not been studied thoroughly. Therefore, the purpose of this study was to evaluate the effect of a typical volleyball practice on anabolic (GH, IGF-I and testosterone) and catabolic hormones (cortisol), and inflammatory mediators (IL-6) in elite, national team level, male and female adolescent volleyball players. Volleyball use
was chosen because it is a very popular team sport for both genders, and involves both aerobic and anaerobic properties. 14.2 METHODS Twenty seven (14 males, 13 females) healthy elite, national team level Israeli junior volleyball players (age range 13.5 - 18 years, Tanner stage for pubic hair 45) participated in the study. All participants played in the Israeli premier junior volleyball league, belonged to the Israeli national junior volleyball team and were members of the Israeli National Academy for Gifted Athletes. The study was performed during the very early phase of the volleyball season. 14.2.1 Exercise protocol Exercise consisted of a typical one hour volleyball practice including 20 minutes dynamic warm-up which included jogging, stretching and running drills at submaximal speed (up to 80% of maximal speed), and additional 20 minutes of volleyball drills. The main part of the practice included seven repetitions of seven consecutive sprints from the back of the volleyball court to the net, maximal jump and a hit of the volleyball over the net in the end of each sprint. Each repetition lasted about 1.5 minutes with one minute rest to collect the balls between repetitions. 14.2.2 Blood sampling Hormonal measurements included circulating levels of the anabolic hormones GH, IGF-I, IGF binding protein-3 (IGFBP-3) and testosterone and the catabolic hormone cortisol. Measurements of inflammatory mediators included the proinflammatory markers IL-6, and the anti-inflammatory marker IL-1 receptor antagonist (IL-1ra). Blood samples were collected before and immediately after the practice. All female participants had regular menses, and blood samples were collected during the early follicular phase of their menstrual cycle (first five days of the cycle). 14.2.3 Statistical analysis Two sample t-test was used to compare baseline and post exercise anthropometric, fitness and hormonal levels between male and female players. Repeated measures ANOVA was used to assess the effect of exercise on circulating components of the GH-IGF-I axis and inflammatory mediators with time serving as the within group factor and gender as the between group factor. Data are presented as mean ± SEM. Significance was set at an alpha level of p!0.05.
