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This article deals with kinematic and kinetic conditions in volleyball attack and identifies loads in the shoulder joint. Joint angles and velocities of individual segments of upper limb were measured with the use of the motion capture system XSENS. Muscle forces and loads in skeletal system were calculated by means of mathematical model elaborated in AnyBody system. Spikes performed by players in the best and worst way were compared with each other. The relationships were found between reactions in shoulder joint and flexion/extension, abduction/adduction and rotation angles in the same joint and flexion/extension in the elbow joint. Reactions in shoulder joint varied from 591 N to 2001 N (in relation to body weight [BW] 83-328%). The analysis proved that hand velocity at the moment of the ball hit (which varied between 6.8 and 13.3 m s-1) influences on the value of reaction in joints, but positions of individual segments relative to each other are also crucial. It was also proved in objective way, that position of the upper limb during spike can be more or less harmful assuming that bigger reaction increases possibility of injury, what can be an indication for trainers and physiotherapists how to improve injury prevention. [ABSTRACT FROM AUTHOR]

Introduction: Eating disorders are an important factor in menstrual cycle disorders in girls. Moreover, low self-esteem among adolescent girls may be a risk factor for eating disorders. The aim of the study was to assess the menstrual cycle, eating habits and self-esteem of Polish adolescents.Methods: The study was conducted from January 2014 to March 2015 and included 623 girls, aged 15-19, from randomly selected junior high schools in Silesia, Poland, in which their menstrual cycle, risk of eating disorders and self-esteem were evaluated. A five-part questionnaire was used to assess basic demographic data, lifestyle and physical activity, gynecological history, as well as Rosenberg Self-Esteem Scale (SES) and Eating Attitude Test (EAT-26).Results: Irregular menstrual cycles were observed in 236 (37.88%) girls; 5.20% presented secondary amenorrhea. Based on the EAT-26 test, 101 (16.21%) girls were indicated being at risk for an eating disorder. Low self-esteem was observed in 340 (54.57%) study girls on the base of SES.Discussion: Girls with irregular menses had higher scores on the EAT-26 test in subscales: EAT-overall score, EAT-diet and EAT-bulimia, while lower scores on the SES. In our study, we did not observe a significant relationship between exercise intensity, body mass, BMI and menstrual cycle regularity. Low self-esteem among adolescent girls may be a risk factor for eating disorders which could interrupt the menstrual cycle. [ABSTRACT FROM AUTHOR]