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Introduction and Objective: One of the strategies that athletes can use to temporarily increase strength and muscle power is post-activation potentiation (PAP) during warm-up. However, the effect of this phenomenon on kinematics of special movement has not been determined. Therefore, the aim of this study is to investigate the acute effect of PAP during warm-up on lower extremity kinematic characteristics during heading in soccer players.
Methodology: The study sample consisted of 24 semi-professional youth soccer players with an average age of 18.67±1.11 years, height 182.32±7.12 cm, mass 74.17±7.46 kg. who performed four different warm-up methods, including PAP-take-off, PAP-landing, combined-PAP, and general warm-up, derived from the stages of soccer heading. Knee and hip angular velocities during the take-off phase, maximum knee flexion angle, and duration of knee joint pause during the landing phase were recorded using a three-dimensional motion analysis device (vicon peak ltd, oxford, vicon UK) with four T20 cameras with a frequency of 1000 Hz. Finally, analysis of variance with repeated measurements and post hoc Bonferroni test were used at a significance level of P<0.05.
Results: There was a significant increase in knee and hip angular velocities following combined-PAP and then PAP-take-off compared to other warm-up programs. Moreover, there was a significant increase in knee flexion angle after PAP-landing compared to other warm-up programs. Additionally, there was a significant increase in the duration of knee joint pause after general warm-up compared to other warm-up programs.
Discussion and Conclusion: PAP-take-off improves jumping performance, while PAP-landing improves landing performance. The combination of these two methods, i.e., combined-PAP, will yield better results overall.

 

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The purpose of this study was to evaluate the effect of quadriceps muscle fatigue on electromyographic activity of selected lower limb muscles during lifting loads using different techniques. Surface electromyography activity of the rectus femoris, vastus latralis, vastus medialis, biceps femoris, semitendinous, gastrocnemius medialis and tibialis anterior muscles of 20 able-bodied women were recorded before and after the quadriceps muscle fatigue using leg-press movement, squat, stoop and strudel techniques with 20% of body weight. Analysis of Variance with repeated measures was used for data analyses (p<0.05). After fatigue when lifting the load, the activity of the rectus femoris, vastus medialis, biceps femoris and gastrocnemius medialis in squat and stoop techniques was significantly different compared to before fatigue condition. But no significant difference was observed between the activity of any of the muscles before and after fatigue in the straddle method. According to the results, it seems that when quadriceps muscle fatigue, the use of straddle technique to lift the load is more appropriate.

 

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Since identifying the best way of performing the Judan Mai-Mawashi-Geri technique is one of the concerns of coaches and karatekas, the aim of this study was to compare the selected kinematic variables of four methods of implementing the Judan Mai-Mawashi-Geri technique by elite male karatekas. Eighteen elite male kumite practitioners voluntarily and purposefully participated in this study. Five markers were attached to the anatomical points of the hitting foot. The four methods of implementing the Judan Mai-Mawashi-Geri technique were filmed by three Hero3 cameras at an imaging speed of 240 Hz. Using SkillSpector software (version: 1.3.2), the resultant of the peak velocity of the lower limb joints, total distance, total velocity, and total acceleration was directly obtained. The one-way analysis of variance and the Bonferroni post-hoc test (p≤0.05) were used with SPSS software (version: 22) for statistical analysis due to the normality of data distribution. The results showed a significant difference in the four methods of performing the Judan Mai-Mawashi-Geri technique in the peak velocity of the pelvic, knee, and ankle joints as well as total distance, total velocity, and total acceleration. According to the research results, the first method of implementation can be recommended as a more efficient technique to kumite practitioners due to its high speed and the possibility of scoring in the shortest time interval and because it closes the opponent’s attack route, compared with Dai and Deashi tactics.
 

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Background and Aims: The surface quality and type are an important factor that may influence the risk of sustaining injuries during running. The aim of the present study was to compare forces excreted on the foot while running on the ground and artificial turf in people with pronated and supinated feet.
Materials and Methods: The statistical population of the present study consisted of healthy men with pronated and supinated feet in Ardabil province. A statistical sample of 30 people aged 20-25 years was selected by available sampling and participated in the present study. Statistical samples were divided into three groups. There were 10 patients in the pronated foot group, 10 people in the supinated foot group and the third group of 10 people as the control group. The navicular drop test was used to measure foot type. A Bertec force plate was used to record ground reaction forces while running on ground and artificial turf at constant speed (about 3.2 m/s). The ground reaction forces in the vertical (Fz), anterior-posterior (Fy) and medio-lateral (Fx) directions were recorded during running.
Results: The results revealed greater medio-lateral ground reaction force at the heel contact in males with pronated feet while running on the ground than that artificial grass. In addition, the time to reach the peak of the vertical component at heel contact during running on grass was greater compared to the ground.
Conclusion: The results showed that the use of artificial turf can improve the risk factors for injury in people with pronated and supinated feet.
 

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Purpose: Neuromuscular and biomechanical factors in ACL injuries are among modifiable risk factors. The purpose of the present study was to evaluate the effect of feedback and feed forward neuromuscular training on balance and isometric strength in female basketball players with a high risk of injury in Kerman.
Method: The present research is semi-experimental, prospective study and the subjects selected objectively based on inclusion and exclusion criteria.  Twenty women basketball players of Kerman city purposely selected and who were randomly divided into two groups of feed forward (age=15.73 ±0.78, weigh =61.38±9.09, height = 164.40 ±6.68) and feedback (age=14.70±1.33, weigh =56.31±8.38, height = 161.66±6.02) The training program designed based on the previous studies and conducted during 8 weeks, three sessions per week (each session 15 to 20 minutes) under the supervision of the examiner. Dynamic balance and isometric knee strength was measured using Biodex system and MMT device. One way ANCOVA was used for data analyze.
Result: The results showed significant differences between pre-post test balance Overall Stability index, internal/external index and Anterior/Posterior index (P=0.001).Significant difference was observed in the strength of quadriceps muscle and hamstring muscle between the two groups of feedback and feed forward exercises (P≥0.05). Also, the results of the paired sample t-test showed that Overall Stability in the feedback  and feedforward group (0.345% and 0.19%), Balance Anterior/Posterior in the feedback  and feedforward group(0.409% and 0.22%) and Balance Medial/Lateral in the feedback  and feedforward group(0.427% and 0.22%) has significantly improvement compared to the pre-test (p<0.002).Isometric Quadriceps strength in the post- test showed an significantly improvement of 2.16% in feedback group and 1.82% in feedforward group compared to the pre-test (P=0.001). Isometric hamstring strength in the post- test showed a significantly improvement of 2.07% in feedback group and 1.95% in feedforward group compared to the pre-test (P=0.001).
Conclusion: It can be concluded that neuromuscular training can enhanced balance and isometric strength, of women and training with feedback has more important  than training with feedforward.
Keywords: neuromuscular exercises, Injury prevention, Anterior cruciate ligament, Feedback

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Introduction and objectives: In the past decades, the control of hand tremors in neurological disorders such as Parkinson's has attracted a lot of attention. The theories of closed-loop deep brain stimulation method are increasing significantly. The purpose of this article is to provide an automatic closed-loop method for the rehabilitation of Parkinson's patients with hand tremor symptoms using machine learning.
Materials and methods: In this article, a mathematical model including muscle model, basal ganglia, cerebral cortex and supplementary motor area is used to simulate tremor. Also, to control hand tremors, a non-integer proportional-derivative-integral controller (non-integer PID) has been used, as well as using the smart Proximal Policy Optimization (PPO) algorithm as a subset of reinforcement learning to adjust the coefficients.
Findings: In addition to reducing hand tremors and automatic learning for use in different levels of the disease, which has given acceptable results compared to other control methods, among the advantages of the Prihadi method is the practical implementation of this method in the real world due to the simplicity of the controller. And also the easy implementation of the intelligent algorithm is due to the automatic adjustment of the coefficients of artificial intelligence networks.
Conclusion: In addition to optimizing output symptoms such as hand tremors compared to other controllers, the proposed intelligent system can also be used for all levels of the disease due to its adaptability, causing a significant reduction in the side effects caused by continuous brain stimulation in the brain stimulation method. It opens in the form of a ring.

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Backgrounds: In order to remain competitive, athletes and coaches are constantly looking for ways to enhance performance. The aim of this study was to investigate the effect of HIFT training and hypoxia mask on maximum oxygen consumption and respiratory efficiency of the players of Iran's men's national ice hockey team.
Method: In this semi-experimental study, 14 players of the Iranian national ice hockey team were divided into two HIFT and HIFT exercise with hypoxia mask groups, then both HIFT groups and HIFT exercise with hypoxia mask, performed HIFT training sessions with 30 seconds repetition and five sets for about an hour, three sessions a week for six weeks. Before and after the training session, anthropometry, body composition, maximum oxygen consumption (VO_2max) and respiratory efficiency (vE/VCO2) were measured using in-body device and gas analyzer. The data were analyzed using the analysis of covariance test at the P<0.05.
Results: The results showed that HIFT exercise and HIFT exercise with hypoxia mask have an increasing effect on VO2max in elite ice hockey men, but there was no difference between the effect of HIFT exercise and HIFT exercise with hypoxia mask on VO2max (P=0.390). After the training, vE/VCO2 decreased in both groups, but there was no difference between the effect of HIFT training and hypoxia mask on vE/VCO2 in elite ice hockey men (P<0.05).
Conclusion: According to the results, it seems that HIFT and HIFT exercise with hypoxia mask may be able to help improve the performance of respiratory system in elite ice hockey men.
 

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Background: In rehabilitation medicine using targeted and personalized approaches are proposed, so that training protocols adjustments, based on gender, age, level of disability and the rate of progress can have more favorable results. The purpose of this study was to investigate the effect of personalized comprehensive rehabilitation training on some induces of physical function in women with MS presenting different levels of disability.
Material & Methods:  In this quasi-experimental study, 92 patients admitted to the MS Society of Shahrekord city were selected and on the basis of disability were categorized into 3 groups of mild, moderate and severe. Then each group was randomly divided into experimental and control group. The personalized comprehensive rehabilitation training program was done 12 weeks, 3 times per weeks. Muscles strength, endurance and speed of walking, were assessed. Independent and Covariance test were used for data analysis.
Results: The results showed that 12 weeks training cause improving in muscles strength, speed of walking in women with MS presenting different levels of disability (p<0.05). Endurance of walking improve significantly in mild group (p<0.05), but in moderate and severe group were not significantly (P˃0.05).
Conclusion: The implementation of the comprehensive rehabilitation exercises affected the recovery of patients with MS and made a significant difference in physical functions of patients.
 

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Introduction: Studies have shown that anterior cruciate ligament injury causes long-term periods of disability and long-term effects; Therefore, it is necessary to adopt preventive measures as well as to have studies that determine the effect of injury prevention programs in improving the performance level of players. Therefore, the purpose of this study was to investigate the effect of eight weeks of the anterior cruciate ligament injury prevention program on the function of elite female kabaddi athletes.
Materials and Methods: This research is semi-experimental based on the application of the intervention variable. 27 female kabaddi athletes with an age range of 18-24 years were randomly divided into two intervention and control groups. The intervention group performed prevention injury and enhance performance program exercises for 8 weeks. The tests were taken before and after eight weeks of the PEP program. These evaluations included T-test, 20-meter sprint test, Y-balance test, sitting and reaching flexibility test, hopping test and functional movement screening test. leven's statistical test was used to check the homogeneity of variances and ANCOVA test was used to evaluate and compare the data.
Findings: The results of the covariance analysis test showed that the intervention group had significantly better scores compared to the control group in the Y-balance tests of the right (p=0.002) and left leg (p=0.001), single leg hopping with right leg (p=0.004) and left leg (p=0.000), crossover hopping with right leg (p=0.023) and sit and reach flexibility test (p=0.003) after eight weeks of exercises In addition, in the tests of sprinting (p=0.649), agility (p=0.073), triple hopping with left leg (p=0.784) and right leg (p=0.204), crossover hopping with left leg (p=0.540) and functional movement screening test (p=0.943) did not show any significant difference between the two groups.
Results: The results of this research showed that the eight-week prevention injury and enhance performance program  has a significant effect on the dynamic balance of the right and left legs, hopping (single leg hopping and crossover hopping of the right leg), and the flexibility of the hamstrings and lower back of elite female kabaddi athletes; But hopping (triple hopping and left leg crossover hopping), speed, agility and FMS test scores have no significant effect.

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Understanding the correct biomechanics of the knee joint during single-leg landing and correcting Incorrect movement patterns can be one of the ways to prevent the recurrence of anterior cruciate ligament injury. Therefore, the purpose of this study is to review the researches that investigated the biomechanics of the coronal plane of the lower limb during multidirectional single leg landing. The relevant articles from valid databases with the keywords Single Leg Landing, Landing, Kinematic, Biomechanics, Return to Sport, Performance Test, Functional Test, Hop Test, Kinetic thematic search methods from 1995 to 2023 were examined. A total of 1022 articles were identified then duplicate studies were eliminated in the next stage, the titles and abstracts of the studies were reviewed and 439 studies were excluded due to inconsistency with the research question. Finally, only 19 articles that met the inclusion criteria were examined. This review showed that only SLL in the forward direction has been investigated in most of the literature using a 3D motion analysis system. There is also no evidence on the biomechanics of other directions of SLL and on the use of 2D motion analysis to evaluate the biomechanics of multidirectional SLL. 

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Different postural stability and functional movements may play an important role in secondary injuries in people with flexible flatfeet compared to people with normal feet. However, the difference between static and dynamic stability and functional movements of people with and without flexible flatfeet has not been investigated. This study compared static and dynamic stability and functional movements of subjects with and without flexible flatfeet and examined the relationship between functional movements and static and dynamic stability. 96 subjects (flexible flatfeet group: 25; normal feet group: 71) functional movement screening test (FMS); Sharpened Romberg balance test and Y balance test were performed. The scores of functional movements and static stability in the normal feet group were significantly higher than the flexible flatfeet group (p≤0.05). The total score of the Y test was not significantly different between the two groups (p≥0.05). In the group of normal feet, a significant correlation was observed between functional movement scores and dynamic stability (p≤0.05). These results show that subjects with flexible flatfeet have different movement performance and static stability compared to subjects with normal feet, but they have similar dynamic stability. It may indicate that there is no connection between static and dynamic stability and these two functions are separate from each other.
 

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The purpose of this research was to design and implement a system for the surveillance of sports injuries in students. Sports injuries of male and female high school students in Ilam province were recorded by physical education teachers using online methods and paper forms during one academic semester. At the end, a questionnaire was used to survey them regarding these methods. The research is of a descriptive-comparative type and Chi-square (x²) was used at the significance level (P<0.05) to analyze the results. A total of 151 injuries were reported, of which 76 injuries (50.4 percent) were registered with the online method, 70 injuries (46.3 percent) with the online paper method, and 5 injuries (3.3 percent) with the paper method. Online registration (146 injuries) is significantly more used than paper registration (75 injuries) (p=0.001) physical education teachers give the reasons for using the online method more: availability, easier working with it, and recovery It is easier to record information. On the other hand, they mentioned the interruption and slowness of the internet speed as things that can cause disruption. According to the results, it seems that the use of online methods is more effective in registering sports injuries in schools.

 

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Disruption of the homeostasis of immune regulatory mediators Aryl hydrocarbon receptor (AhR) and Ornithine decarboxylase-1(ODC-1) is involved in the pathogenesis of multiple sclerosis (MS). Physical activities play a role in controlling and improving the symptoms of MS. This study was conducted in order to investigate the effect of 4 weeks of physical activity in an enriched environment on the gene expression of AhR and ODC-1 in the cerebellum tissue of an MS mice model. This experimental study was conducted on 30 female C57BL/6 mice. Mice were divided into 3 groups of 10 including 1) healthy control, 2) experimental model of MS and 3) physical activity in enriched environment. After induction of experimental autoimmune encephalomyelitis (EAE), the third group lived in the enriched environment for 4 weeks. Body weight and clinical score were recorded daily from induction until 28 days. The gene expression of AhR and ODC-1 in the cerebellum was measured by RT-PCR method. Statistical analysis of the data was performed using one-way analysis of variance at a significance level of less than 0.05. Activity in the enriched environment significantly decreased the gene expression of AhR compared to the EAE group (P=0/02) and also decreased the gene expression of ODC-1, but it was not statistically significant (P=0/28). Also, the clinical score improved significantly after activity in the enriched environment (P= 0/001). Lifestyle change and activity in the enriched environment led to the down regulation of the gene expression of AhR and ODC-1, and it improved the clinical score of animals.

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Lack of sensory information, muscle weakness, lack of coordination and position sense of joint are predictor factors of musculoskeletal disorders, and it seems that sports activities will have an effect on posture control and joint proprioception. Therefore, the purpose of this research was the effect of Pilates exercises on balance and proprioception in female students. 98 female students between the ages of 18-25 years-old and weight 57.92±7 kg voluntarily participated in this study after completing the written consent form. Of these, 91 healthy students were placed in the experimental group and 7 students with sports exemption (with medical conditions such as: recent surgery for refractive errors of the eye, cysts, etc.) were placed in the control group. The position senses of ankle and knee joints was measured using the active reconstruction test of the ankle and knee angles and static balance was measured using the Sharpened Romberg test before and after 16 intervention sessions. Wilcoxon test was used to determine the difference in pre-test and post-test (intra-group difference) and covariance test was used to compare between groups (of course, the data were normalized earlier). The results showed that after the intervention, in the experimental group, static balance increased significantly in the post-test compared to the pre-test. The position sense of dorsiflexion, plantarflexion of ankle joint and knee flexion position sense in the experimental group increased significantly in the post-test compared to the pre-test. Also, the results of the covariance test showed that there is a significant difference between the two groups in the post-test in the variables of static balance and position sense of dorsiflexion and plantarflexion of ankle and position sense of knee flexion. According to the adjusted average in the post-test stage, the experimental group performed better than the control group. The results showed that Pilates exercises are suitable for improving ankle and knee proprioception and improving postural control in teenagers and young adults. 

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Volleyball players are looking to apply their force at a short  time speed  to  transfer more  diagonal  and vertical blows  on the ball  so  that  you land  on the  opposing  team's field more quickly and make it  difficult for the  opposing  team players to  receive. It seems that various types of resistance training can improwe the vertical force of the spike skill.
Therefore the aim of the current study is to compare the effects of two types of resistance training (exercises with cable machines and exercise with barbells and free weights) on vertical force and impulse caused by diagonal hit on spike skill in college girl volleyball players. The present study method was semi-experimental. The statistical samples in this study included 45 girl volleyball players from university of Mohaghegh Ardabili. In three groups of 15 in groups 1 and 2 strength training intervention for two days a week, in 7 strenght movements with a cable bodybulding machine and barbell, dumbbell, and medicine training tools, observing the principle of overload in three movement intensities: 80%, 5 repetition, 90%, 2 repetition, 100%, one maximum repetition and in the third group in the form of a control group were identified. Strength training as an independent variable and vertical force and impulse as a dependent variable. Bertek force plate was used to record ground reaction forces. The table was used to adjust height, the invisible thread and the ball for the dominant hand shot in the volleyball players. In this study, ANOVA test was used with a significance level of 0.05. The effects of the force resulting from the diagonal impact on the ball in line with the vertical force of the ground reaction were significant in intervention group 1 (p< 0.008) and intervention group 2 was not significant (p< 0.133).The effect of the impulse time factor in the strength training group was significant in the vertical component of the ground reaction in intervention group1 (P<0.030) and in intervention group 2 (P<0.023). The difference between the groups in the intervention group shows the effect of the vertical force factor in the intervention group 1 with the impact factor (v = 0.016) compared to the group 2 also, in the impulse factor, impact factor was effective in intervention group1 (v = 0.190) and strength training in intervention group 2 (v = 0.167).  It seems that barbell and medicine ball strength exercises increased force in diagonal strikes and produce the maximum vertical force in the shorter time to the ball in the spike skill of the diagonal strike of the volleyball players.

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Abstract
Introduction and purpose: Jumping motor tasks in people with motor control defects are probably associated with incomplete movement patterns, which can be related to non-collision injuries of the lower limbs. In relation to these people, it has been recommended that the design of exercise protocols should also be done with the aim of controlling and improving functional defects. Therefore, the aim of the present study is to investigate the eight-week training program of feedback on the biomechanical variables of athletes with selected motor control defects in landing jump tasks.

Materials and methods: The present study is a randomized clinical trial study before and after the intervention. 34 male recreational athletes with movement control defects (dynamic knee valgus and quadriceps dominance) were selected based on the study criteria and then randomly assigned to control groups with a ratio of 1:1 (age range, 28.10±4.70years; height, 171±5.49cm;  mass, 76.83±5.81kg; and BMI, 22.12± 1.54kg/m² ) and feedback group (age range, 29.80±3.61years; height, 173.80 ± 4.70cm; mass, 78.33±4.64kg; and BMI, 21.40±1.77 kg/m² ).Electromyography data (vastus medialis, vastus lateralis, gluteus medius, Tensor fasciae latae and biceps femoris) and lower limb kinematics (knee valgus angle) were recorded while the participants performed the landing jump movement tasks (vertical jump, tuck and countermovement) in the two previous stages. From the protocol and after the protocol, they performed jumping exercises for two months. In addition, external feedback (first by using educational videos and then verbally while doing the task (place the knee in line with the toes, press the knee towards the wall (external source)) during the two months of the training program and during Performance of movement tasks was presented to the feedback group. To analyze the data, two-way analysis of variance and Bonferroni statistical tests were used for each movement task at a significance level of P < 0.05.

Findings: The results of the study indicated an increase in the electrical activity of the VM and GM muscles and a decrease in the electrical activity of theVL, BF and TF muscles in different phases of jumping in the feedback group. As an example, the results of the Bonferroni post hoc test showed a significant improvement in the feedback group in the amount of electrical activity of the VM muscle (effect size = 0.57, p = 0.001) and GM(effect size = 0.53, p = 0.002). In the eccentric phase, there was a significant improvement in the amount of electrical activity of the VM muscle (effect size = 1.05, p = 0.001) and GM(effect size = 0.77, p = 0.001) in the maximum knee flexion phase and improvement The electrical activity of VM muscle (effect size = 1.71, p = 0.001) and GM (effect size = 1.19, p = 0.001) had significance in the landing moment phase during vine jump. Also, the feedback group showed a decrease in knee valgus angle in the frontal plane (P < 0.05).
Conclusion: The results of the present study showed that feedback has an effect on kinematic and electromyographic parameters and improves the jump-landing biomechanics of the lower limbs in people with knee motor control defects and can be used to correct incomplete movement patterns in jump-landing tasks. be used However, for a general conclusion, more studies are needed in different groups and different sports levels, as well as more samples.

 

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Background and Aims: Running is one of the most important activities for soldiers, and boots play an effective role in this activity. The aim of the present study was to investigate the effects of three types of military boots mileage on ground reaction force variables during running.
Materials and Methods: The current research was a clinical trial. 15 healthy male students (20-25 years old) used three different types of used and new boots. Using Bartec force plate with dimensions (60 x 40 cm²), ground reaction forces were measured in vertical (Fz), anterior-posterior (Fy) and medio-lateral (Fx) directions while running at constant speed. Two-way ANOVA was used for statistical analysis at a significance level of 0.05.
Results: Results demonstrated significant main effects of "Time" for FX_HC (P=0.001, d=0.407), FX_PO (P=0.001, d=0.674), TTPFX_PO (P=0.001, d=0.394) and TTPFY_PO (P=0.031, d=0.226). Findings showed significant main effect of group for FZ_HC (P=0.027, d=0.163) and TTPFY_HC (p=0.035, d=0.150). Furthermore, significant group-by-time interactions was found for FZ_HC (P=0.001, d=0.404) and FX_PO (P=0.014, d=0.272).
Conclusion: The results of this research showed that using military boots, the vertical ground reaction force, the medio-lateral force at heel contact and the peak medio-lateral force were increased. The increase of this value can be related to fracture injuries caused by pressure and patella femoral pain. The results of this study showed that the type of boots can be effective in preventing lower limb injuries. Therefore, using new operational boots is suggested for the military application.
 

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The main goal of this research was to design and evaluate the features of a "home-based weightless fitness device with digital adjustment" for performing muscular exercises in a home environment. To achieve this goal, a combined quantitative and qualitative approach was employed, and a detailed assessment of the device's performance was conducted. In the initial stage, existing fitness equipment, resistance training methods, and technological advancements were investigated. This review provided fundamental information for the initial design of the device. Subsequently, using design software such as Rhino Cross 6 and AutoCAD 2018, precise three-dimensional models and initial prototypes were created. To validate the device's resistance, a digital force gauge was utilized, measuring the displayed force in eight different settings with the resistance adjusted on the device, allowing for the calculation of device deviation from standard and error margin. Furthermore, to assess the device's reliability three seated movements—leg press extension, seated chest press, and seated front raise bicep curl—, each performed with eight consecutive repetitions using a 10-kilogram weight. The results of Pearson's correlation coefficient (0.9) showed that the instrument has high reliability. Also, the results of intra-correlation reliability coefficient (0.8) showed that the device has good reliability and high accuracy in the produced resistance in different movements and repetitions. Ultimately, this research introduces an effective tool for muscular exercises in a home setting. With its precise resistance adjustment capability and versatility in exercise options, the device empowers athletes to perform exercises with greater precision. Overall, this study yields practical and implementable results, potentially playing a crucial role in enhancing the health and fitness of athletes and the general community.
 
 

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Background and purpose: Determining specific abilities and skills in volleyball players depends on the amount of anthropometric, physiological, biomechanics and psychological characteristics of the players in this field and is vital for improving the performance of sports skills in them. Since by comparing these important factors in the group of teenagers and young adults, it is possible to guide teenagers towards success factors in youth and adulthood, the purpose of this research was to compare the main characteristics of elite teenage and young male volleyball players.
Methods: 30 male members of the national youth volleyball team of the Islamic Republic of Iran (15 youths and 15 teenagers) were examined in terms of their main anthropometric, biomechanics, physiological and psychological characteristics with the aim of evaluating and determining the main components and comparing them.  In order to determine he main components of the evaluated indicators, first the PCA statistical method and then the independent t statistical method were used to compare the two groups(0.05≥p).
Results: Among the main indices of anthropometric, biomechanical, physiological and psychological characteristics, only the physiological index of maximum heart rate showed a significant difference between the two groups (0.05≥p).
Conclusion: It seems that the main differences of volleyball players in these two age groups are more related to experience in the game and mastery in the implementation of various skills and techniques, and all these main features can be found in the talent search process of this group of young people.