Incremental training intensities increases loads on the lower back of elite female rowers

Lumbar-pelvic kinematics change in response to increasing rowing stroke rates, but little is known about the effect of incremental stroke rates on changes in joint kinetics and their implications for injury. The purpose of this study was to quantify the effects of incremental rowing intensities on lower limb and lumbar-pelvic kinetics. Twelve female rowers performed an incremental test on a rowing ergometer. Kinematic data of rowers’ ankle, knee, hip and lumbar-pelvic joints, as well as external forces at the handle, seat and foot-stretchers of the rowing machine were recorded. Inter-segmental moments and forces were calculated using inverse dynamics and were compared across stroke rates using repeated measures ANOVA. Rowers exhibited increases in peak ankle and L5/S1 extensor moments, reductions in peak knee moments and no change in peak hip moments, with respect to stroke rate. Large shear and compressive forces were seen at L5/S1 and increased with stroke rate (P < 0.05). This coincided with increased levels of lumbar-pelvic flexion. High levels of lumbar-pelvic loading at higher stroke rates have implications with respect to injury and indicated that technique was declining, leading to increased lumbar-pelvic flexion. Such changes are not advantageous to performance and can potentially increase the risk of developing injuries.     

Motorische Leistungsfähigkeit von Kindern und Jugendlichen in Deutschland

Motor performance is an important health resource. Review articles revealed a decline of motor performance of approximately 10?% between 1975 and 2006. In the past most of the data available for such comparisons came from ad hoc studies with non-standardized methods. Within the framework of the ”Motorik-Modul“ (MoMo) study as part of the German Health Interview and Examination Survey for Children and Adolescents (KiGGS), it is possible for the first time to directly compare two cohorts in the ages of 4–17 years in a nationally representative database for Germany. The aim of this article is to report changes in motor performance of children and adolescents in the time period 2003–2006 (cohort baseline n = 4528) compared to 2009–2012 (cohort wave 1, n = 2820). Overall, it is clearly shown that the motor performance of children and adolescents in Germany did not decrease within the observational period of 6 years. The comparison of mean values of the baseline cohort compared to those of wave 1 showed that 28 out of 52 mean values of the two cohorts with a high probability did not differ based on 95?% confidence intervals (CI). In 24 out of the 52 mean values positive changes could be noted based on the individual 95?% CI values. There were more positive changes in primary school aged children than in other age groups. Within these positive changes, most effect sizes were small to medium. The results indicate that recent activities aiming at elevating motor performance levels may have started to make an impact and should be expanded, also in secondary schools. The comparative cohort study presented in this article is currently being checked by the ongoing MoMo wave 2 survey of 2014–2017.     

Bedingungen der Bindungswirkung inkrementeller Normen in Fußballvereinen

Sports clubs depend on the pooling of resources by their members. The supportive distribution of the resources within a club is facilitated in particular by the effectiveness of incremental standards. A basic prerequisite for a fair distribution of resources is a minimum of community spirit among the members. Based on a nationwide survey of football clubs and an ordinal logistic regression model, factors were determined that reflect the extent of the community spirit within a club. The opening up of the club by payment to players and perceived problems with acquiring and binding of volunteers are associated with a reduction of community spirit. In contrast, the perception that the club activities can be continued in the long term shows a positive correlation to a highly developed community spirit.     

标记系统及学术文本处理的未来（一）

标记事务影响着学者们对思考与写作系统的采纳使用。程序性标记和表示性标记会阻碍这一进程的发展,描述性标记则通过简化机械性任务,让学者们将注意力集中于内容上的做法,以加快这一进程。     

A channel distortion model for video over lossy packet networks

Error-resilient video communication over lossy packet networks is often designed and operated based on models for the effect of losses on the reconstructed video quality. This paper analyzes the channel distortion for video over lossy packet networks and proposes a new model that, compared to previous models, more accurately estimates the expected mean-squared error distortion for different packet loss patterns by accounting for inter-frame error propagation and the correlation between error frames. The accuracy of the proposed model is validated with JVT/H.264 encoded standard test sequences and previous frame concealment, where the proposed model provides an obvious accuracy gain over previous models.     

Accuracy of activPAL Self-Attachment Methods

This study examined the accuracy of self-attachment of the activPAL activity monitor. A convenience sample of 50 participants self-attached the monitor after being presented with written material only (WMO) and then written and video (WV) instructions; and completed a questionnaire regarding the acceptability of the instructional methods. Participants positioned the monitor lower than the instructed position on the thigh (WMO ?5.15 ± 2.75 cm, WV ?4.16 ± 2.15 cm; p = .008 difference) and approximately 2 cm laterally from the thigh midline (WMO 1.90 ± 0.92 cm; WV 2.08 ± 1.24 cm). The orientation of the device was positioned correctly along the midline (within < 1° of vertical). Acceptability was high for both instructional methods although preference was shown for the WV instruction. In conclusion, participants consistently self-attached the activPAL close to the intended placement with either instructional method. The addition of video instruction produced a slightly more accurate attachment and was preferred by the participants.     

A review of tennis racket performance parameters

The application of advanced engineering to tennis racket design has influenced the nature of the sport. As a result, the International Tennis Federation has established rules to limit performance, with the aim of protecting the nature of the game. This paper illustrates how changes to the racket affect the player-racket system. The review integrates engineering and biomechanical issues related to tennis racket performance, covering the biomechanical characteristics of tennis strokes, tennis racket performance, the effect of racket parameters on ball rebound and biomechanical interactions. Racket properties influence the rebound of the ball. Ball rebound speed increases with frame stiffness and as string tension decreases. Reducing inter-string contacting forces increases rebound topspin. Historical trends and predictive modelling indicate swingweights of around 0.030–0.035 kg/m² are best for high ball speed and accuracy. To fully understand the effect of their design changes, engineers should use impact conditions in their experiments, or models, which reflect those of actual tennis strokes. Sports engineers, therefore, benefit from working closely with biomechanists to ensure realistic impact conditions.     

Synchronized lower limb kinematics with pelvis orientation achieves the non-rotational shot

A non-rotational (NR) shot is now a well-known scoring move in soccer. To execute the NR shot, it is necessary to deprive the ball of any rotational forces during the impact phase. To execute the NR shot, it is natural that the force vector acting from the foot would pass through the ball’s center of gravity; however, the coordinated motion of the lower limb joint’s angular displacement and the pelvis is still unclear. The aim of this study is to estimate the coordinated leg and pelvis motion during the NR shot as compared to that during instep kicking. Four right-leg dominant college league players were asked to perform a NR shot and an instep kick a total of 10 times each. Hip, knee, and ankle joint angular displacements in the sagittal plane and pelvis yaw and roll rotational motions during both types of kicks were calculated with 14 IR reflective markers using a 3D real-time motion analysis system with a 250-Hz sampling. The Euclidean distances of the joint space of the NR shot and the instep kick were also calculated to detect similarities in the coordinated motion of the lower limb. The results showed that the lower limb joint motions in the sagittal plane were not different; however, the pelvis roll and yaw motions were apparently different, and these phenomena could simulate a pendulum motion with changes in both the vertical and horizontal displacements. These results suggest that the coordinated motion of the lower limb joint’s angular displacement shows high similarity between the NR shot and the instep kick, and the pelvis roll and yaw synchronized orientation is essential for achieving the NR shot.     

Elite wheelchair rugby: a quantitative analysis of chair configuration in Australia

Limited recommendations of wheelchair configurations for court sports have been identified in the published literature. To accommodate the wide range of impairments in wheelchair rugby, players are given a point score that reflects their impairment. Players have regularly been grouped as high-, mid-, or low-point players in research, with high-point players having greater levels of muscle function compared with other classifications. This research documented the wheelchair configurations of elite Australian wheelchair rugby players across classification groups. Significant differences (p < 0.05) were found for increased seat height and decreased seat depth for high-point players compared with low- and mid-point groups, respectively. Low-point players displayed reduced wheelchair mass compared with high- and mid-point players, as well as increased frame length. Camber angles showed no significant differences across the classification groups. The incorporation of anthropometric measures, such as the elbow angle at the top dead center, was also investigated. While elbow angle showed no significant differences, seat height-to-total arm length ratio was higher for high-point players. Participants also completed surveys detailing their perception of the effect of altering wheelchair configurations. It is suggested that wheelchair configurations should consider an individual’s anthropometrics, impairment, training history, and court role to promote optimal performance, with predictive modeling having the potential to reduce the associated time and cost.