مجله بیومکانیک ورزشی
سال سوم شماره 4 (زمستان 1396)

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.
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.
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.
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.

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 athlete's performance. In the swimming tournament starting on time and correctly, one of the factors that plays an important role in the success of swimmers, especially speed swimmers. The aim of this study was Comparison of selected kinematic variables frontand rear- weighted track start of elite male swimmers.
Fourteen male elite male swimmers with an average age of 17.86±1.92 years were targeted and available among those who had better starters 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. Used a top speed of 100 fps video camera to detect body position and biomechanical parameters during the performance two start techniques.the statistical methods were Kolmogorov-smirnov test to chek for normal distribution of data and T-test for comparison between two types of kinematic quantities start with 0.05 alpha levels.
Findings indicated that flight distance were significant difference between two start techniques (P Because of the difference in flight distance and Time off the platform in two types of startes, coaches and swimmers can use either of the two startes depending on the type of competition (Speed and endurance of swimming).

Volleyball players due to the high jump and bend the waist to hit and Continuous shot to be like spokes from the top of the head, spine and increased lumbar lordosis are impaired. The aim of this study was to investigate Efficacy of the Yumeiho therapy massage on Repositioning error, Range of motion trunk Flexation and functional power in women volleyball players with Hyper lordosis.
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 massage and control (no exercise) groups. The amount of Repositioning error by the spinal mous, Range of motion by spinal mouse and muscle strength by dynamometer was used. The experimental group strength training did three times a week for eight weeks. Paired t-test for within group comparison, independent t-test was used for comparison between groups.
Significant difference was observed between the two groups in the Repositioning error, Range of motion of trunk Flexation and extensor and flexor of trunk muscle.
results showed that the effect of Yumeiho therapy massage on repositioning error, Flexation range of motion trunk and functional power had a significant. It therapists recommended to include Yumeiho therapy massage in order to enhance these variables.

The center of mass is dependent on the distribution of mass and 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 of girls and boys aged 6 to 12 years.
Participants in this study were 192 healthy girls and 192 healthy boys who were studying in Isfahan, from which 154850 students were selected through cluster sampling. For this purpose, their mass was measured with a bascule, variables related to stature with meter and center of mass were measured with a weighing machine based on calculating torques. with respect to the multivariate regression assumptions and stepwise method, the variables that had the greatest impact on the center of mass were selected and models were proposed whit them.
The girl’s equation, shows that the stature, body mass index and sitting height per stature ratio, can be used to estimate the center of mass of girl children, and the estimated center of mass for boy children, with stature, sitting height and sitting height per stature ratio, form equation is possible.
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.
It can be said that, in order to calculate the center of mass of child, instead of using multiple and sometimes difficult, time consuming and costly methods and calculations, the equations obtained in this study should be used.

The purpose of this study was investigate the effect of dynamic knee valgus during overhead squat, on hip and ankle joints muscle strength and range of motion in basketball players.
In this study 35 healthy basketball players (with the mean age 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 last year were the volunteers. The peak force and the passive range of motion were measured rspecively by a hand-held dynamometer and a goniometer. The Independent 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.
Compared by 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).
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 of during overhead squat and modify dynamic knee valgus.

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 between three shooting fields including archery, pistol and air rifle.
Twenty­-four available shooters of 20-40 years old with more than 3 years of professional training history were participated in this study. The electrical activity of subjects in during 60 and 90 degree abduction with dominant hand were evaluated by using surface electromyography and scapular symmetry position by using Modified Lateral Scapular Slide test. Data were analyzed by independent t-test, ANOVA.
In both positions of 60 and 90 degree abduction, the activity of the serratus anterior muscle in archery group was significantly more than the pistol and air rifle ones (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 (PDiscussion and The different positioning of hand and shoulder in the different fields shooters 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.