KICKING IN SOCCER

Kicking as the defining action of soccer has gained huge interest within the scientific community with respect to practice, coaching, science and technology. This paper focuses on current knowledge of soccer kicking, including its biomechanical description, skill execution, kicking techniques, performance criteria, and measurement technology .Additionally, it refers to a fairly new research aspect, the influence of soccer footwear on the kicking movement and consequently on kicking success as it has been shown that soccer footwear alters the biomechanics of kicking. Finally, future directions of research are suggested that are helpful to enhance the fundamental understanding of kicking

Risk and Protective Factors for Bullying Victimization among Sexual Minority Youths

Sexual minority youths: SMY) suffer higher rates of bullying victimization and related mental health and academic problems compared to their heterosexual peers. At present, little research has investigated the modifiable and non-modifiable risk and protective factors that are associated with lower frequencies of bullying victimization and victim distress for SMY. This study utilized a risk and resilience theoretical framework and addressed the following research questions among a community-based sample of SMY: 1) What are the associations between risk and protective factors and the frequencies of total and four types: i.e., verbal, relational, electronic, and physical) of bullying victimization? 2) What are the associations between the frequencies of total and four types of bullying victimization and mental health problems and academic outcomes? and 3) To what extent do modifiable risk and protective factors: MRPF) moderate the association between total bullying victimization and mental health problems and academic outcomes? A cross-sectional, quantitative design was utilized for this study. Structured, face-to-face interviews were conducted with SMY: N = 125) aged 15 to 19 years old and recruited from two Midwest, community-based organizations. Bivariate analyses were performed to identify associations between: 1) risk and protective factors and bullying victimization: total and type) and: 2) bullying victimization: total and type) and mental health problems and academic outcomes. Multiple regression analyses were performed to explore the potential moderating influence of MRPF on the relationship between total bullying victimization and mental health problems and academic outcomes. For research question 1, SMY who reported higher levels of classmate support and positive school climate experienced significantly lower frequencies of bullying victimization. Older SMY reported significantly lower levels of physical and verbal bullying victimization than their younger counterparts. Similarly, African American and Caucasian SMY reported lower levels of physical and verbal bullying victimization compared to their Hispanic, Native American, and multiracial counterparts. Emotional, physical, and sexual child abuse were identified as significant risk factors for bullying victimization. For research question 2, SMY who experienced higher frequencies of bullying victimization: total and type) reported significantly higher levels of psychological distress, anxiety, and depression. Further, those who experienced higher frequencies of bullying victimization: total and type) had significantly higher odds of having seriously considered suicide, attempted suicide, and experienced disciplinary actions in school. SMY who reported higher frequencies of bullying victimization also had significantly lower grade performance. Overall, physical bullying victimization had the strongest associations with mental health problems and academic outcomes, while electronic bullying victimization consistently had the weakest associations. For research question 3, classmate support was found to be a significant moderator of total bullying victimization and grade performance, such that SMY with higher levels of classmate support experienced less of a decline in grades as the frequency of total bullying victimization increased compared to SMY with lower levels of classmate support. Last, parent support was found to be a significant moderator of total bullying victimization and psychological distress. High levels of parent support had a protective effect on psychological distress only at a low frequency of total bullying victimization. Parent support appeared to be unable to protect SMY from poorer psychological distress as the frequency of total bullying victimization increased. This study is one of the first to examine the protective factors present in the lives of SMY and contributes to the bullying literature for SMY by identifying the modifiable and non-modifiable risk and protective factors that may be used to inform multi-level, anti-bullying interventions. Individual-level intervention components may include provision or referral to mental health services to address the high levels of mental health problems and histories of child abuse and neglect often present in the lives of SMY. In addition, peer-level intervention components may include the adoption of peer mentoring programs that foster classmate support and increase the rates at which classmates intervene to stop incidents of bullying victimization at school. Last, school-level intervention components may include strategies that promote positive school climates for SMY through the adoption of anti-bullying and anti-discrimination policies that provide specific protections for sexual minority students, teachers, and staff

Batch Reinforcement Learning on the Industrial Benchmark: First Experiences

The Particle Swarm Optimization Policy (PSO-P) has been recently introduced and proven to produce remarkable results on interacting with academic reinforcement learning benchmarks in an off-policy, batch-based setting. To further investigate the properties and feasibility on real-world applications, this paper investigates PSO-P on the so-called Industrial Benchmark (IB), a novel reinforcement learning (RL) benchmark that aims at being realistic by including a variety of aspects found in industrial applications, like continuous state and action spaces, a high dimensional, partially observable state space, delayed effects, and complex stochasticity. The experimental results of PSO-P on IB are compared to results of closed-form control policies derived from the model-based Recurrent Control Neural Network (RCNN) and the model-free Neural Fitted Q-Iteration (NFQ). Experiments show that PSO-P is not only of interest for academic benchmarks, but also for real-world industrial applications, since it also yielded the best performing policy in our IB setting. Compared to other well established RL techniques, PSO-P produced outstanding results in performance and robustness, requiring only a relatively low amount of effort in finding adequate parameters or making complex design decisions

ANKLE AND KNEE COORDINATION FOR SINGLE-LEGGED VERTICAL JUMPING COMPARED TO RUNNING

Similar basic movement patterns in ground reaction forces and ankle frontal plane kinematics of single-legged vertical jumping (JUMP) compared to running (RUN) have already been identified in earlier investigations. To broaden these findings, lower extremity kinematics of 25 subjects were recorded executing RUN and JUMP. Special focus was laid on the knee and ankle coordination of tibial endorotation and ankle eversion as well as on knee and ankle flexion/extension by applying a modified vector coding technique. RUN and JUMP demonstrated similar knee and ankle joint coordination patterns. However, differences in coupling angles unveiled phases, where joint coordination of ankle eversion/tibial endorotation was adjusted in JUMP. By comparing knee and ankle coordination of JUMP in healthy athletes with athletes suffering from anterior knee pain, common in sports with high jumping occurrences, key differences in execution leading to this overuse injury might be unveiled

A Benchmark Environment Motivated by Industrial Control Problems

In the research area of reinforcement learning (RL), frequently novel and promising methods are developed and introduced to the RL community. However, although many researchers are keen to apply their methods on real-world problems, implementing such methods in real industry environments often is a frustrating and tedious process. Generally, academic research groups have only limited access to real industrial data and applications. For this reason, new methods are usually developed, evaluated and compared by using artificial software benchmarks. On one hand, these benchmarks are designed to provide interpretable RL training scenarios and detailed insight into the learning process of the method on hand. On the other hand, they usually do not share much similarity with industrial real-world applications. For this reason we used our industry experience to design a benchmark which bridges the gap between freely available, documented, and motivated artificial benchmarks and properties of real industrial problems. The resulting industrial benchmark (IB) has been made publicly available to the RL community by publishing its Java and Python code, including an OpenAI Gym wrapper, on Github. In this paper we motivate and describe in detail the IB's dynamics and identify prototypic experimental settings that capture common situations in real-world industry control problems

KINEMATIC COMPARISON OF KICKING A STATIONARY AND ROLLING BALL

Much biomechanical research has examined stationary ball kicking in soccer. However, most kicks in games are performed on a rolling ball. It is important to evaluate this kick as findings for stationary ball kicking might not transfer. The aim of this study was to compare stationary and rolling ball kicks. Nine skilled soccer players performed three kicks under four pre-kick ball conditions (stationary, rolling 30? relative to kick direction, rolling 90? relative to kick direction, dribbling). Lower body kinematics were captured using VICON Nexus (250 Hz), analysed in Visual 3D and compared via a factorial ANOVA. No significant difference existed for foot speed at ball contact, or leg kinematics between stationary and rolling ball conditions Further, kinematics did no change regardless of the approach angle of the ball indicating kinematics do not change regardless of pre-kick ball conditions. Future stationary-rolling ball comparison work should examine kinetics, support leg mechanics and foot to ball interaction

Biomechanical locomotion adaptations on uneven surfaces can be simulated with a randomly deforming shoe midsole

Background: A shoe with unsystematic perturbations, similar to natural uneven terrain, may offer an enhanced training stimulus over current unstable footwear technologies. This study compared the instability of a shoe with unpredictably random midsole deformations, an irregular surface and a control shoe-surface whilst treadmill walking and running. Methods: Three-dimensional kinematics and electromyography were recorded of the lower limb in 18 active males. Gait cycle characteristics, joint angles at initial ground contact and maximum values during stance, and muscle activations prior to initial contact and during loading were analysed. Perceived stability, injury-risk and energy consumption were evaluated. Instability was assessed by movement variability, muscular activations and subjective ratings. Results: Posture alterations at initial contact revealed active adaptations in the irregular midsole and irregular surface to maintain stability whilst walking and running. Variability of the gait cycle and lower limb kinematics increased on the irregular surface compared to the control across locomotion types. Similarly increased variability (coefficient of variation) were found in the irregular midsole compared to the control for frontal ankle motion (walk: 31.1 and 14.9, run: 28.1 and 11.6), maximum sagittal knee angle (walk: 7.6 and 4.8, run: 2.8 and 2.4), and global gait characteristics during walking only (2.1 ± 0.5 and 1.6 ± 0.3). Tibialis anterior pre-activation reduced and gastrocnemius activation increased in the irregular midsole compared to the control across locomotion types. During running, peroneus longus activation increased in the irregular midsole and irregular surface. Conclusions: Results indicate random shoe midsole deformations enhanced instability relative to the control and simulated certain locomotion adaptations of the irregular surface, although less pronounced. Thus, a shoe with unpredictable instability revealed potential as a novel instability-training device

A Benchmark Environment Motivated by Industrial Control Problems

In the research area of reinforcement learning (RL), frequently novel and promising methods are developed and introduced to the RL community. However, although many researchers are keen to apply their methods on real-world problems, implementing such methods in real industry environments often is a frustrating and tedious process. Generally, academic research groups have only limited access to real industrial data and applications. For this reason, new methods are usually developed, evaluated and compared by using artificial software benchmarks. On one hand, these benchmarks are designed to provide interpretable RL training scenarios and detailed insight into the learning process of the method on hand. On the other hand, they usually do not share much similarity with industrial real-world applications. For this reason we used our industry experience to design a benchmark which bridges the gap between freely available, documented, and motivated artificial benchmarks and properties of real industrial problems. The resulting industrial benchmark (IB) has been made publicly available to the RL community by publishing its Java and Python code, including an OpenAI Gym wrapper, on Github. In this paper we motivate and describe in detail the IB's dynamics and identify prototypic experimental settings that capture common situations in real-world industry control problems

STUD LENGTH AND STUD GEOMETRY OF SOCCER BOOTS INFLUENCE RUNNING PERFORMANCE ON THIRD GENERATION ARTIFICIAL TURF

The purpose of this study was to evaluate the influence of different stud lengths and stud geometries of soccer boots on soccer specific running performance. The study involved performance testing by running through two functional traction courses and corresponding subjective testing. Variables of this study were objectively measured running times and perception ratings of running performance. 15 experienced soccer players participated in the study. Players run slower when performing with shorter studs (