Islamic Azad University, Hamedan Branch Journal of Sport Biomechanics 2476-4906 3 4 2018 3 1 Introducing a Model for Determining the Center of Mass in Children Aged 6 to 12 in Isfahan 5 15 FA Akbar Taherian Masoumeh Shojaei College of Physical Education and Sport Sciences, Al-Zahra University, Tehran, Iran. Afkham Daneshfar Maryam Sharifdoust Objective: The center of mass is dependent on the distribution of mass and the properties of the length of the upper parts of the body to the lower parts of the body. This plays a fundamental role in the body's balance, which can be measured in various ways. The purpose of this study was to provide a model for determining the center of mass in girls and boys aged 6 to 12 years. Methods: Participants in this study were 192 healthy girls and 192 healthy boys who were studying in Isfahan, who were selected through cluster sampling from among 154850 students. For this purpose, their mass was measured with a bascule, and the variables related to stature with a meter and the center of mass with a weighing machine based on calculating torques. The variables that had the greatest impact on the center of mass were determined through a multivariate regression assumptions and stepwise method and some models were proposed. Results: The model obtained for girl’s, showed that the stature, body mass index and sitting height per stature ratio, could be used to estimate the center of mass, and that the estimated center of mass for boy children, with stature, sitting height and sitting height per stature ratio, could be obtained through an equation. Conclusion: It is recommended to use the obtained equations in order to estimate the center of mass of children's bodies, rather than using multiple and sometimes difficult, time-consuming and costly methods and calculations.

Islamic Azad University, Hamedan Branch Journal of Sport Biomechanics 2476-4906 3 4 2018 3 1 The Effect of Dynamic Knee Valgus during Overhead Squat on Distal and Proximal Knee Joints Muscle Strength and Range of Motion in Basketball Players 17 27 FA Hemn Mohammadi Department of Physical Education and Sports Sciences, Faculty of Humanity Sciences, University of Kurdistan, Sanandaj, Iran. Hassan Daneshmandi University of Guilan Mohammadhoein Alizadeh University of Tehran Ali Shamsimajlan Objective: The purpose of this study was to investigate the effect of dynamic knee valgus during overhead squat, on hip and ankle joints muscle strength and range of motion in basketball players. Methods: In this study, 35 healthy basketball players (with the mean age of 20.98± 1.99, height 183.27 ± 6.64 cm and mass 75.31 ± 9.24 kg), in the control group (n = 18) and dynamic knee valgus group (n = 17) with no lower-extremity injury during the past volunteed to take part in the study. The peak force and the passive range of motion were measured rspecively by a hand-held dynamometer and a goniometer. The Independent samples T-test at the significance level of 0.05 was used to determine the difference of strength and range of motion in the control and dynamic knee valgus groups. Results: Compared with the control group, the dynamic knee valgus group showed to have a greater strength of the hip external rotation and extension (respectively P=0.000, P=0.004), smaller Plantarflextion strength (P=0.001), smaller dorsiflexion range of motion with knee bent (P=0.021), and greater external rotation of the hip (P=0.002). Conclusions: The results showed that the dynamic knee valgus group exhibited tight and weak ankle musculature, and as appeared, training interventions focused on improving strength and range of motion of the ankle can improve lower extremity kinematics during overhead squat and can modify the dynamic knee valgus.

Islamic Azad University, Hamedan Branch Journal of Sport Biomechanics 2476-4906 3 4 2018 3 1 Comparison of Selected Kinematic Variables in the Front- and Rear- Weighted Track Start of Elite Male Swimmers 29 37 FA Mohamad-fazel Sabaghi Masoud Mirmoezzi Department of Motor Behavior, Faculty of Physical Education and Sport Science, Islamic Azad University Branch of Central Tehran, Tehran, Iran Parasto Mohamadian Objective: Over recent years, due to scientific advances in various aspects of sport, rapid development and improvement has taken place in sport performance standards as well as athletes' performance. In the swimming tournaments, on-time and correct start, plays an important role in the success of swimmers, especially speed swimmers. The aim of this study was comparising selected kinematic variables in front and rear- weighted track start of elite male swimmers. Methods: Fourteen elite male swimmers with an average age of 17.86±1.92 years selected from among an available sample of those who had better starts and had the right foot (dominant legs) place in this study. The following kinematic parameters were analysed: take off angle, take off velocity, entry angle, entry velocity and flight distance. Using a top speed of 100 fps video camera to detect body position and biomechanical parameters during the performance of two start techniques. The statistical procedures to analyze the data included Kolmogorov-Smirnov test to chek for normal distribution of the data and T-test for comparing the kinematic quantities of two types of start with at 0.05 alpha levels. Results: The findings indicated that there was a significant difference in the flight distance between two start techniques (P<0.05) and that the distance at Frontand- weighted track start was more than the distance at rear- weighted track start. As to the other components, including angles and speeds from the platform, angle and speed of entering the water, no significant differences were found between two types of front- and rear- weighted track starts (p <0.05). Conclusion: Because of the difference in flight distance and time off the platform due to the positioning of the center of gravity in the two types of starts, coaches and swimmers can use either of the two starts depending on the type of competition (speed and endurance of swimming).

Islamic Azad University, Hamedan Branch Journal of Sport Biomechanics 2476-4906 3 4 2018 3 1 Comparing the Electrical Activity of Serratus Anterior and Upper Trapezius Muscles and the Scapular Symmetry in Three Fields of Shooting 39 49 FA Safoura Heshmati Department of Sport Injuries & Corrective Exercise, Faculty of Sport Sciences, University of Guilan, Rasht, Guilan, Iran. Hassan Daneshmandi University of Guilan seyyed Hosseein Hosseini Objective: The purpose of the present study was to compare the serratus anterior and upper trapezius muscles activities in the shoulder abduction and scapula symmetry position in three shooting fields including archery, pistol and air rifle. Methods: Twenty­-four available shooters between 20 to 40 years old with more than 3 years of professional training history participated in this study. The electrical activity of muscles during 60 and 90 degree abduction with dominant hand were evaluated using surface electromyography in scapular symmetry position by using Modified Lateral Scapular Slide test. Data were analyzed through independent samples t-test and ANOVA. Results: In both 60 and 90 degree abduction positions, the activity of the serratus anterior muscle in archery group was significantly more than those in the pistol and air rifle positions (P< 0.05). However, the activity of the upper trapezius muscle did not indicate any significant difference in the three groups (P> 0.05). There were significant differences between distances of two lower scapular angles from the vertebral column in positioning of the hand on the hip in air rifle, and in positioning of the hand in 90 degree elevation, in archery and pistol groups (P< 0.05). Also there were significant differences in the scapular symmetry in positioning of the hand on the hip, and in 90 degree elevation, between archery and rifle groups, and between rifle and pistol groups (P< 0.05). Conclusion: The different positioning of hand and shoulder in different shooting fields as the dominant postures during exercises and competitions, can be one of the most important causes of the difference in muscles electrical activity and scapular symmetry among these groups.

Islamic Azad University, Hamedan Branch Journal of Sport Biomechanics 2476-4906 3 4 2018 3 1 Efficacy of the Yumeiho Therapy Massage on Repositioning Error, Range of motion of Trunk Flexion and the Functional power in Female Volleyball Players with Hyper Lordosis 51 61 FA Yousef yarahmadi Department of Sport Biomechanics and Sport Injuries, Faculty of Physical Education and Sport Sciences, University of Kharazmi,,Tehran, Iran. Razeih Mirbaghri Maliha Hdadnzhad Objective: Due to their repeated attempts in high jumping and bending the waist to hit the ball from the top of the head, volleyball players suffer from spine impairments and increased lumbar lordosis. The aim of this study was to investigate the efficacy of the Yumeiho therapy massage on repositioning error, Range of motion in trunk flexion and functional power in women volleyball players with Hyper lordosis.  Methods:  the present study was a quasi - experimental study with a pretest-posttest design with a control group. A total of 30 postmenopausal women with hyper lordosis were purposefully selected and randomly divided into two groups of 15 individuals: a treatment and control groups. The amount of repositioning error and range of motion by spinal mouse and muscle strength was calculated by dynamometer. The experimental group strength training did three times a week for eight weeks. Paired samples t-test was run for within group comparisons and independent sample t-test was used for between group comparisons. Results: Significant differences were observed between the two groups in the repositioning error, Range of motion of trunk flexion and extensor and flexor of trunk muscle. Conclusion: Results showed that Yumeiho therapy massage would have a significant effect on repositioning error, flexion range of motion trunk and the functional power. Thus therapists can recommend the Yumeiho therapy massage in order to enhance these variables.

Islamic Azad University, Hamedan Branch Journal of Sport Biomechanics 2476-4906 3 4 2018 3 1 Investigation Two Type of Absolute and Coordination Variability of Upper Limb Joints through Learning 63 73 FA Zahra Entezari Khorasani Department of Motor Behavior, Faculty of Physical Education and Sport Science, Shahid Beheshti University, Tehran, Iran Alireza Farsi Mohamad Kazem Vaez Mousavi Behroz Abdoli Objective: Theories are in paradox in relation to the variability pattern with being skilled. Then this research has investigated two types of absolute and coordination variability during basketball free throw learning, with isolating mechanical and dynamical degrees of freedom. Methods: Twenty self-declared participants were randomly assigned into two groups: physical practice and control. Experimental group practiced in 12 sessions of 50 trials. Absolute variability was measured by root mean square error and coordination variability was assessed using vector coding. Result: The physical practice group was significantly better than control group in accuracy scores. Results in relation to the absolute variability revealed, only in the ankle joint, physical practice and control groups are different (P=0.037, F=5.07) and the pattern of changes supported Bernstein's theory. In the case of coordination variability, there was no difference between the two groups in any of the joints coupling. But the wrist-elbow pattern of changes in physical practice group was in accordance with the theory of dynamic systems. Conclusion:  Overall, it seems that wrist movement and wrist-elbow coordination are very important in free throw shooting skill. Also, the findings of this study showed that it is necessary to isolate mechanical and dynamical degrees of freedom in the measuring and discussing the Theories regarding the movement variability.