Sport Sciences for Health (18247490)18(1)pp. 219-225
Purpose: Kinematic variables identify movement patterns and are used to compare successful versus unsuccessful performances that cause to better understanding of performance optimization techniques. Therefore, the aim of this study was to compare the angular kinematic variables in successful and unsuccessful performances in gymnastic somersault for identifying the optimization performance of this technique. Materials and methods: Eleven skillful male gymnasts (Avg. age 11.5 ± 3.7 years, height 123 ± 38.9 cm, weight 36.5 ± 16.9 kg and experience 4.64 ± 3.7 years) participated in this study. They were required to perform somersault and their performances were labeled as successful and unsuccessful performances according to referees’ scores. Then, the recorded performances were analyzed and the desired kinematic parameters were calculated. Results: The results showed that the average of ankle angles at two instances of initial contact and toe off were higher in successful performances than unsuccessful ones. Besides, the minimum values of hip and knee angles and also the maximum values of knee angles were significantly higher in successful performances. The shoulder angles at two instances of initial contact and toe off in successful performances were also found to be less than unsuccessful ones, but, the range of shoulder motion in successful performances were greater than unsuccessful performances. Conclusions: According to the results of this study, the maximum and minimum values of the major joints involved in this technique, range of their motions, and angular velocities of them are identified as the effective factors in this technique. © 2021, The Author(s), under exclusive licence to Springer-Verlag Italia S.r.l., part of Springer Nature.
Smart Structures and Systems (17381584)27(4)pp. 641-650
In the present study, the generation of electrical energy from induced vibrations in a composite beam with piezoelectric layer are studied. Accordingly, using Euler-Bernoulli beam theory and considering two types of air damping (external damping) and structural damping (internal damping), the equations of motion for sandwich beam are obtained and then using the Kantorovich method, the output voltage relations for a composite beam with a piezoelectric layer are extracted. After validating the analytical results with the results in the literature, the effect of various parameters such as external fluid flow rate, fiber angle, and how the piezoelectric layer composite beams are arranged on energy harvesting. Also, the maximum oscillation amplitude are investigated. The results show that by using composite materials and with proper layer design and fiber angle in each layer, a different equivalent modulus of elasticity can be created in the composite beam, which will change the normal frequency of the system and the output voltage range of the circuit. The results show that the angle of the fibers has a significant effect on the damping coefficient of the structure, flexural stiffness, natural frequency and finally energy harvesting. According to the results, it can be seen that the minimum value of voltage per use of fibers with an angle of 50 degrees and the maximum amount of voltage per use of fibers with an angle of zero degrees are occurred. © 2021 Techno Press. All rights reserved.
Asian Journal Of Sports Medicine (20087209)12(2)
Objectives: The aim of this study was to evaluate the validity and reliability of introducing a new activity-based balance index using a triaxial accelerometer during activity. Methods: Twenty seven soccer players (age: 14.5 ± 0.4 years old, body mass: 58.3 ± 9.3 kg, height: 172 ± 8 cm) who participated in the national premier league were recruited. The participants were tested for their balance, activity, and skill in four tests: (I) one leg stance; (II) dynamic Y balance; (III) running; and (IV) dribbling slalom. The acceleration of the body was recorded using an accelerometer during those tests. By processing acceleration data, a new activity-based balance index (ABI) was calculated based on the velocity, acceleration, and position index of soccer players. Using intra-class correlation coefficients (ICC), reliability was calculated. Results: Reliability was high (ICC = 0.87-0.89; 95% CI = 0.77-0.93) in calculating ABI for the three activities performed in the tests. A significant positive correlation between ABI and both static and dynamic balance scores (r = 0.62, P = 0.002) was observed. Further-more, negative correlation was found significantly between ABI and dribbling scores (r =-0.61, P = 0.026) and Y Balance test (r = 0.6, P = 0.002). Conclusions: In conclusion, the introduced ABI demonstrates great potential to determine balance and skill scores based on accelerometer-based measures. © 2020, Author(s).
Aging Clinical And Experimental Research (17208319)32(9)pp. 1757-1765
Background: Impairment of postural adjustments in elderly is associated with decreased functional mobility, balance confidence and quality of life. Aims: We studied the effects of anticipatory postural adjustments focused training on postural preparation, balance confidence and quality of life of the elderly. Methods: It was a single-blind randomized controlled trial. The sample included 60 males with history of falling (at least once in the past 6 months). They were matched and randomly assigned into three groups: perturbation, balance, and no training. The electrical activity of the muscles was measured by electromyography. The Activities-specific Balance Confidence (ABC) scale and the SF-36 questionnaire were used to assess balance confidence and quality of life, respectively. Repeated-measures ANOVA was used for data analysis (significant level 0.05). Results: The type of training had significant interaction effect on muscle latency (F(2, 46) ≥ 71.06, P ≤ 0.001, η2 ≥ 0.75). Compared to the other two groups, perturbation training group showed significantly more improvement in ABC scale (F(2, 46) = 14.94, P ≤ 0.000, η2 ≥ 0.39). It also significantly showed more improvement than no training group in all areas of SF-36 questionnaire, except for mental health (F(2, 46) ≥ 6.56, P ≤ 0.03, η2 ≥ 0.22). Conclusions: Our findings support the use of perturbation training, as it reduced the probability of falling (by decreasing muscle latency and increasing posture preparation), improved the balance confidence for daily activities, and improved the quality of life. © 2019, Springer Nature Switzerland AG.
Iranian Journal of Ageing (1735806X)15(2)pp. 236-245
Objectives Improving balance and motor function in the elderly for preventing falling and its irreparable consequences has attracted the attention of many researchers in the field of aging. The purpose of the present is to investigate the effect of an exercise program based on Anticipatory Postural Adjustments (APAs) on postural control and motor function of the elderly. Methods & Materials In this experimental study conducted in 2017, the study population consists of 38 eligible male elderly people with a history of falls at least once in the last six months living in Isfahan, Iran in two groups: 18 in the test group (mean age =70.4±3.2, mean height=65.3±6.2 cm, mean weight= 65.3±4.2 kg) and 15 in the control group (mean age =69.6±3.1 years, mean height =167±5.5 cm, mean weight =67.3±6.8). A foot-scan device was used to measure their postural control, and the Timed Up and Go (TUG) test was taken to measure their motor function. Data were analyzed in SPSS v. 20 software using repeated measures ANOVA at the significance level of P≤0.05. Results The exercise program significantly improved the mean postural control scores in anterior/posterior direction from 28.1±6.2 to 20.5±2.4 (F=8.21, P≤0.05), in medial/lateral direction from 17.1±1.5 to 13.2±2.9 (F=13.4, P≤0.05), and in overall from 312.4±21.2 to 285.8±17.5 (F=10.02, P≤0.05); It also improved the mean TUG test score from 13.3±2.1 to 10.1±1.0 (F=16.02, P≤0.05). The experimental group showed a better performance than the control group after exercise in TUG test and postural control parameters (P≤0.05). Conclusion An 8-week exercise program focused on APAs can be effective in improving postural control and motor function of the elderly. © 2020, Iranian Journal of Ageing. All Rights Reserved
Journal Of Research In Health Sciences (22287809)19(3)
Background: Hyperkyphosis is often accompanied by forward head and shoulder postures. Together, these three disorders are called “Upper Cross Syndrome (UCS)”. We aimed to perform a photogrammetric analysis of UCS among teachers and to determine the effects of National Academy of Sports Medicine (NASM) exercises with ergonomic training interventions on the syndrome. Study design: A semi-experimental study. Methods: Photogrammetric analysis was performed using the UCS software among teachers in order to determine the angles of forward head, rounded shoulders, and hyperkyphosis. Twenty-three teachers were selected purposefully and enrolled in Fasa City in 2018. They were randomly divided into experimental (n=12) and control (n=11) groups. Experimental group attended 12 wk of NASM exercises with ergonomic intervention but the control group did not participate in any regular exercise. The data were analyzed using paired t-test and differential independent t-test (P[removed]
Procedia Engineering (18777058)2(2)pp. 2563-2567
The barbell trajectory of snatch weightlifting has been investigated by several researchers. They suggested three optimal trajectory patterns (type A, B and C). But, there is no agreement for introducing the best overall trajectory. One probable reason would be this idea that the selected criterion used by the previous researchers might not be appropriate. Therefore we used a mathematical approach to judge between the conflicts. We made a multi-segments biomechanical model to evaluate the snatch motions while considering the selected mechanical cost. This method is an appropriate tool for coaches to examine several trajectories for making a good decision.
Simulating the snatch weightlifting technique by means of dynamic formulation and optimizing this movement using Genetic Algorithm is the main purpose of this study. Snatch weightlifter is modeled by an open kinematic chain. The problem is defined as the optimization of the movement of this model from the first position to the predefined second position while considering the specific optimum criterion like minimizing the muscular effort. The results for two different weight class are represented in the forms of kinematic and kinetic data like trajectory of barbell and actuating joint torques. Because of some similarities between the results and experimental observations by other researches we conclude that our method can be able to model the real situation. This model can be used to optimize the performance of the weightlifters and it could give us some useful advice about the most effective technique. © 2008 IEEE.
American Journal of Applied Sciences (discontinued) (15469239)5(5)pp. 524-531
Mathematical modeling and optimizing of snatch lift technique based on dynamic synthesis, is the aim of this study. The barbell trajectory is proposed as the performance index, evaluated experimentally by several researchers who have introduced some optimum trajectories according to the percentage of their owners' successes. Since none of the mechanical parameters were considered into the optimum trajectories, we develop a mechanical approach to fulfill this lack. Therefore, we use a biomechanical model comprised of five links to obtain the optimum trajectory of snatch weightlifting by means of minimizing a criterion function. To achieve this goal, we should solve the differential equations representing the model motion simultaneously with equations representing the performance criterion; therefore we use the optimal control approach via Pontryagin Maximum Principle (PMP) formulation. The performance criterion is defined as minimizing the sum of actuating torques of all joints during the whole snatch. The barbell trajectory of our optimized model is approximately similar to one which could be observed in experimental results. By comparing the results of this theoretical model with experimental observations of other researchers, it could be concluded that we have introduced a good predictive model. Using the biomechanical characteristics of any specific weightlifter as the input data to this model and comparing the results with the same weightlifter's experimental data can help the coaches to improve the performance of weightlifters. © 2008 Science Publications.
Mathematical modeling and optimization of snatch technique based on dynamic synthesis is the main purpose of this study. The barbell trajectory is proposed as the main index which was evaluated experimentally by several researchers who introduced optimum trajectory according to percentage of their owners' success. We believe that in optimizing the barbell trajectory we should consider the mechanical principles. Therefore we use a five-link biomechanical model to evaluate its behaviour and to predict the optimum barbell trajectory which minimizes the specific mechanical criterion by using genetic algorithm (GA) which is theoretically and empirically proven to provide a robust search in complex spaces, thereby offering a valid approach to problems requiring efficient and effective searches. Comparing the results of this model and experimental observations of other researchers, we show an improvement to introduce a good predictive model. Using this model can help the coaches to improve the performance of weightlifters.
