Islamic Azad University, Hamedan Branch Journal of Sport Biomechanics 2476-4906 9 3 2023 12 1 Comparison of External Focus Instructions Based on Mechanics and Performance in the Vertical jump: Examining the constrained action hypothesis 178 191 FA Seyyed Fardin Qeysari Department of Motor Behavior, Faculty of Physical Education and Sports Sciences, University of Tehran, Tehran, Iran. Somayeh Emamrezaii Department of Sport Physiology, Faculty of Physical Education and Sport Sciences, University of Lorestan, Lorestan, Iran. Amineh Eslamizad Department of Motor behavior, Faculty of Physical Education and Sports Sciences, Central Tehran Branch, Islamic Azad University, Tehran, Iran. Seyyed Kamal Qeysari Department of Physics, Faculty of Physics, University of Tehran, Tehran, Iran. Objective In some situations, however, the goal of the skill is to correct movement mechanics, and in these specific scenarios, external focus instructions should be specific to mechanics. External focus instructions based on performance do not have a positive effect on motion mechanics. The purpose of this study was to investigate the effect of external focus instructions based on mechanics and performance in the vertical jump movement: Examining the constrained action hypothesis. Methods Twelve male professional volleyball players (average age 24.0±1.92 years; average weight 73.5±8.7 kg) voluntarily participated in this research. Subjects performed the vertical jump movement with all their strength in two external focus situations (1- performance-based external focus, 2- mechanics-based external focus) on the force plate. In order to investigate the electromyography activity of the right abdominal muscle, an electromyography device was used, which was simultaneous with the force plate device in terms of time. The ground reaction force data based on time by the force plate were used to obtain the different time phases of the vertical jump and to calculate the jump height. Results The results of the paired t-test showed that the jump height in the performance-based external focus condition was significantly higher than the mechanics-based external focus condition (P<0.001). Also, the focus of external attention based on mechanics compared to the focus of external attention based on performance caused a significant increase in the electrical activity of the right abdominal muscle during the concentric phase (P<0.001). However, there was no significant difference in the eccentric phase of the electrical activity of the right abdominal muscle between the two conditions (P=0.233). Conclusion These results indicate that performance-based external focus instructions lead to greater automaticity of movement and improved performance. However, it is not useful for improving movement mechanics, and for this purpose, external focus instructions based on movement mechanics should be used.

Islamic Azad University, Hamedan Branch Journal of Sport Biomechanics 2476-4906 9 3 2023 12 1 The Effect of Extra Functional Exercises with and without Functional Muscle Stimulation on the Lumbar Lordosis in Women Aged 20-30 Years in Tabriz 192 202 FA Amir Ghiami rad Department of Movement Behavior, Faculty of Sports Sciences, Tabriz University, Tabriz, Iran. Solmaz Jafari Amirkhiz Sports Sciences Department, Shams Institute of Science and Technology, Tabriz, Iran. Behnam Shahbazi Department of Sports Biomechanics, Faculty of Sports Sciences, Bu- Ali Sina University, Hamadan, Iran. Objective Increased lordosis in the lumbar is one of the causes of poor posture and back pain. The purpose of this research is to investigate the effectiveness of extra-functional exercises with and without functional stimulation of the muscles around the lumbar joints in women with increased lumbar lordosis. Methods The conducted research is quasi-experimental and applied. The statistical population consisted of 46 women divided into two equal groups within the age group of 20 to 30 years in Tabriz city, each having a lordosis angle of 40 degrees. Evaluation of lordosis angles (control and experimental groups) was measured using a flexible ruler, tilt meter, and McGill test (pre-test). Then, for 6 weeks, the experimental group performed three sessions of exercise protocol and muscle functional stimulation per week, while the control group only received exercises similar to those of the experimental group (post-test). Statistical analysis was conducted using independent t-tests and paired t-tests at a significance level of 0.05. Results In the experimental group compared to the control group, there was a significant difference in lumbar lordosis and anterior pelvic tilt components in the post-test (P<0.05). Conclusion Based on the obtained results, it can be acknowledged that central stability exercises (Extra Functional) along with muscle functional stimulation can yield beneficial results in improving lumbar biomechanics in cases of lordosis and hyperlordosis disorders within the statistical population.

Islamic Azad University, Hamedan Branch Journal of Sport Biomechanics 2476-4906 9 3 2023 12 1 The Effect of Eight Weeks of Resistance Training on the Record of Young Sprint Runners 204 218 FA Bager ShojaAnzabi Department of Sports Physiology, Faculty of Educational Sciences and Psychology, University of Mohaghegh Ardabili, Ardabil, Iran. Ebrahim Piri Department of Sports Biomechanics, Faculty of Educational Sciences and Psychology, University of Mohaghegh Ardabili, Ardabil, Iran. Reza Farzizadeh Department of Sports Physiology, Faculty of Educational Sciences and Psychology, University of Mohaghegh Ardabili, Ardabil, Iran. Objective Resistance training is a fundamental method for inducing muscle growth, enhancing functional capacity, and preventing injuries among athletes. The aim of this study was to investigate the effects of an eight-week resistance training program on the performance progress of young sprint runners. Methods This semi-experimental study involved the selection of 34 young runners who were then randomly assigned to either a training group or a control group. The exercise group underwent resistance training sessions for eight weeks. Parameters including absolute power, relative power, lower limb power, and 100m sprint records were analyzed. The Multivariate Analysis of Variance (MANCOVA) test was employed to compare the pre-test and post-test results of the two groups. Additionally, the correlated t-test was used to compare post-test results between the groups. The paired t-test was also utilized to compare pre-test and post-test results within the training group. All statistical analyses were conducted using SPSS version 26. Results The findings revealed that the exercise group, which underwent resistance exercises with weights for eight weeks, experienced a significant improvement compared to the control group. Furthermore, factors such as absolute strength, relative strength, lower limb strength, and limb telemetry showed significant increases. Additionally, athletes in the training group achieved faster sprint records. Conclusion Resistance training promotes muscle hypertrophy, enhances power, and improves sprint records. Therefore, it can be concluded that athletes involved in track and field events utilize resistance training as part of their preparation to enhance performance and achieve record-breaking results.

Islamic Azad University, Hamedan Branch Journal of Sport Biomechanics 2476-4906 9 3 2023 12 1 Comparison of Biomechanical Models for Roundhouse Kicking in Skilled Martial Arts Students of Taekwondo and Wushu (Sanda) 220 232 FA Mahdi Najafian Razavi Department of Physical Education and Sport Sciences, Mashhad Branch, Islamic Azad University, Mashhad, Iran. Meysam Rezaei Department of Physical Education and Sport Sciences, Mashhad Branch, Islamic Azad University, Mashhad, Iran. Objective Participation in martial arts such as Karate, Taekwondo, Kung Fu, and Wushu has increased recently, and it is possible that determining the difference between performing different kicks in skilled athletes can be of great help to coaches and beginner athletes for better performance and prevention of sports injuries. Methods Twelve athletes in two fields of Taekwondo and Wushu were divided into groups of six people. A motion analysis device was used to measure the variables of roundhouse kicking with the foot. Paired t-tests were used to analyze the data at a significance level of 0.05 for statistical analysis. Results Findings showed that there is no significant difference between the duration of the kicking (leg return), the maximum speed of the foot until the moment of kicking, the speed of the foot at the moment of strike, the angle of the knee at the moment of strike, and thigh internal rotation angle (p>0.05). However, significant differences were observed in the variables of maximum knee angle in the flexion axis, hip flexion angle at the moment of strike, lateral angle (Y&Z) of the thigh at the moment of strike, the amount of internal rotation of the hip (in terms of angle), the amount of lateral rotation to the outside of the hip, the maximum amount of internal angular changes of the thigh in terms of time, and maximum amount of hip lateral angular changes in terms of time (p<0.05). Conclusion According to the obtained results, it seems that there is a difference between some kinematic variables of rotational kicking in Taekwondo and Wushu disciplines, which is probably due to the type of kicks in Taekwondo and Wushu, as each of these sports probably requires different techniques.

Islamic Azad University, Hamedan Branch Journal of Sport Biomechanics 2476-4906 9 3 2023 12 1 Evaluation of Spatio-Temporal Gait Variability during Obstacle Crossing in Parkinson's Disease 234 250 FA Elaheh Azadian Department of Motor Behavior, Hamedan Branch, Islamic Azad University, Hamedan, Iran. Mahdi Majlesi , Department of Sport Biomechanics, Hamedan Branch, Islamic Azad University, Hamedan, Iran. Ali Fatahi Department of Sports Biomechanics, Central Tehran Branch, Islamic Azad University, Tehran, Iran. Rezvan Bakhtiyarian Department of Sport Biomechanics, Hamedan Branch, Islamic Azad University, Hamedan, Iran. Objective IObstacle crossing and navigating through complex environments is a challenging task in daily life and has been identified as a major cause of falls in individuals with Parkinson's disease (PD). The aim of this study is to assess the variability in spatio-temporal variables of gait in patients with Parkinson's disease when crossing obstacles. Methods This descriptive study included 15 men with Parkinson's disease and 17 age-matched healthy men who participated in this study through convenience sampling. Spatio-temporal parameters of gait during normal walking and obstacle crossing were evaluated using a motion analysis system with four cameras (Vicon, Oxford Metrics, Oxford, UK). The results were analyzed using three-way analysis of variance (ANOVA) and SPSS software with a significance level of p < 0.05. Results The results showed that cadence and walking speed were lower and swing time, stance time, stride time, step time, single support time, and double support time were higher in the PD group compared to the control group (p < 0.05). The difference between the two groups was significant in the variability coefficient of variables such as double support time, single support time, stride time, step length, and percentage of opposite foot contact with the ground. Crossing obstacles also resulted in increased stride time, stance time, step length, and stride length compared to normal walking, and increased variability in swing time, single support time, stride time, and step time. Conclusion Crossing obstacles in individuals with PD resulted in reduced walking speed and increased double support time, which are among the most important risk factors for falls. Additionally, greater variability during normal walking or obstacle crossing, accompanied by decreased cognitive functions in the PD group, indicates an increased risk of falls during challenging activities.

Islamic Azad University, Hamedan Branch Journal of Sport Biomechanics 2476-4906 9 3 2023 12 1 Football Biomechanics and Performance Enhancement: A Systematic Review 252 270 FA Farhad Nazari Department of Sports Biomechanics, Faculty of Sport Science and Physical Education, Central Tehran Branch, Islamic Azad University, Tehran, Iran. Ali Fatahi Department of Sports Biomechanics, Faculty of Sport Science and Physical Education, Central Tehran Branch, Islamic Azad University, Tehran, Iran. Objective Football players and their coaches are constantly thinking about improving the performance and quality of football for their fans. The purpose of this systematic review was to investigate the use and role of training tools and specialized exercises in enhancing the performance of football players and to review the results, analyses, and suggestions from various studies in the field of football biomechanics and performance enhancement. Methods Articles were searched through electronic sources in Persian specialized databases: Google Scholar, Magiran, Civilica, Irandoc, SID, ISC and in English databases: Science Direct, Google Scholar, PubMed, and Scopus. The keywords for the search included biomechanics, football, performance enhancement, and their synonyms, which were searched in both Persian and English. Results After reviewing the entire text of the articles, a total of 87 articles were evaluated and studied in three areas, including the use of different training tools and exercises to improve performance, as well as the analysis and suggestions resulting from research in football biomechanics and performance improvement. Conclusion The findings showed that performance improvement in soccer players is achieved through the use of training tools and specific exercises. Plyometric exercises and theraband stretches improve proprioception and the strength of the ankle joint muscles in soccer players. An increase in technical skills is observed in small-sided games, leading to higher ball possession rates. The FIFA +11 program has a significant impact on the speed, dribbling speed, shot accuracy, agility, and vertical jump of soccer players.