Sport selection in under-17 male roller hockey

Abstract

Characteristics of 32 international and 41 local under-17 (U-17) (14.5–16.5 years) roller hockey players were considered in the context of discrimination by competitive level using training history, anthropometry, skeletal maturation, and several laboratory and field performance tests. More international (42%) than local (22%) players were advanced in maturity status. International players had slightly less hockey experience (years), but had more practice sessions and match time (minutes) during the season. Local players were shorter and attained better performance in the 25-m dash, while international players performed better in sit-ups, ball throw and 20-m shuttle run. The fatigue index derived from the Wingate anaerobic test was higher among local players, while peak torques of knee extension and flexion were greater in international players. Stepwise discriminant function correctly classified 85% of players by competitive level based on grip strength, ratio of eccentric and concentric knee extension, number of training sessions, playing time and fatigue index. The results suggested an interaction among strength, anaerobic fitness and training plus game time as factors in discriminating international from local level players and by inference in the selection and development of youth roller hockey players.     

The influence of electrostimulation on mechanical and morphological characteristics of the triceps surae

The present study assessed the effects of training using electrostimulation of muscle (EMS) on the torque‐angular velocity and torque‐angle relationships, and the cross‐sectional area (CSA) of the triceps surae. Twelve physical education students, divided into two groups (6 control, 6 experimental), participated in the experiment. The EMS sessions were undertaken using a ‘Compex‐type’ stimulator. Flexible elastomer electrodes were used. The current used discharged pulses lasting for 200 μs at a frequency of 70 Hz. The durations of contraction and rest were 5 and 15 s, respectively. The session lasted for 10 min for each muscle. The training regimen was three sessions per week for 4 weeks. Biomechanical tests were performed with the Biodex (Biodex Corporation, Shirley, NY, USA) isokinetic ergometer. Plantar flexions of the ankle over a concentric range of voluntary contractions were performed at different angular velocities (1.05, 2.10, 3.14, 4.20, 5.23 and 6.28 rad s^‐1) and maximum voluntary isometric contractions were held for 5 s at several ankle flexion angles (–30°, –15°, 0° and 15°; 0° corresponds to foot flexion of 90° relative to the leg axis). The peak value of the torque was recorded. Morphological tests consisted of measuring the CSA of the triceps surae on the right leg, 15 cm below the tibial protuberance, by a computerized tomography technique. The torque‐velocity relationship was seen to shift significantly upwards after EMS training. The increase in the isometric torque observed after EMS training was greater in dorsiflexion than in plantarflexion. No change was noted in the CSA of the muscle. It appears that the increase in strength following EMS training is not related to an increase in the contractile matter. These observations show that EMS training for 4 weeks develops dynamic and static contractile properties of the muscle. Neural mechanisms may account for these adaptations.     

The effects of imagery training on fast isometric knee extensor torque development

Abstract

We hypothesized that imagery training would improve the fast onset of neuromuscular activation and thereby fast knee extensor isometric torque development. Forty young healthy participants, not involved in strength training, were assigned to one of four groups: physical training, imagery training, placebo training or control. The three training groups had three 15 min sessions per week for 4 weeks, with a 90° knee angle but were tested also at 120°. At 90° knee angle, maximal torque increased (～8%) similarly in all three training groups. The torque–time integral (contractile impulse) over the first 40 ms after torque onset (TTI40) increased (P < 0.05) after physical training (by ～100%), but only at 90°. This increase was significantly different from the delta values (change pre to post) in the control and placebo groups, whereas delta values in the imagery group were similar to those in the placebo group. The increases in TTI40 following physical training were related (r ² = 0.81, P < 0.05) to significant increases of knee extensor rectified surface EMG at torque onset (EMG40). In conclusion, only physical training led to a knee angle specific increase of contractile impulse that was significantly different from placebo and controls and that was related to improved onset of neuromuscular activation.     

Yearly Changes in the Body Composition and Muscular Strength of High School Wrestlers

Abstract

The purpose of this investigation was to determine the yearly changes in body composition as well as absolute and relative isokinetic forearm flexion and extension strength of high school wrestlers. Evaluations of body composition (underwater weighing) were performed on 27 high school wrestlers prior to three consecutive seasons. In addition, isokinetic forearm flexion and extension strength values at 180°/s (Cybex II) were available for 20 of the subjects. The mean ages at the times of laboratory testing were 15.5 (± .5), 16.5 (± .5), and 17.5 (± .5) years. Repeated measures ANOVA or ANCOVA with Tukey post-hoc comparisons were used to locate significant (p<.05) differences across age for height, body weight, relative fat, body density, fat weight, fat-free weight, absolute muscular strength, and muscular strength covaried for body weight and fat-free weight. There were yearly increases in all variables except fat weight, forearm flexion covaried for fat-free weight and forearm extension covaried for fat-free weight. The results of this study indicated that the improved wrestling performance and the increase in weight classification which normally occurs during high school are, in part, a function of yearly changes in body composition and muscular strength.     

Isokinetic Leg Flexion and Extension Strength of Elite Adolescent Female Track and Field Athletes

Abstract

Sixty-two elite adolescent (age: 16.39 ± 1.62 yrs) female track and field athletes volunteered to be measured isokinetically for peak torque of the leg flexors and extensors. The sample included 16 throwers, 11 jumpers, 12 middle-distance runners (> 400 m), and 23 sprinters. A Cybex II isokinetic dynamometer was used to measure dominant leg strength at 180°/sec. One-way ANOVA revealed significant between group differences for absolute flexion and extension (Nm), extension/body weight (Nm/Kg), and extension/lean body weight (Nm/Kg). Scheffe post-hoc comparisons showed that, for absolute leg extension strength, throwers were stronger than middle-distance runners (by 54.4%), sprinters (35.6%), and jumpers (23.6%). For absolute leg flexion movements, throwers were stronger than middle distance runners (37.4%) and sprinters (32.1%). Jumpers had greater extension peak torque values than middle-distance runners relative to body weight (14.0%), and throwers were stronger than middle-distance runners for extension/lean body weight (14.9%)). No other comparisons were significant. However, when strength was expressed relative to body weight or lean body weight, there were few differences between events for flexion or extension. Given that absolute strength scores were correlated with body weight and lean body weight, peak torque/body weight or peak torque/lean body weight may be more sensitive than absolute values as indicators of underlying factors (such as training status or fiber type composition) responsible for the differences in muscular strength between groups.     

Does a land-based compensatory strength-training programme influences the rotator cuff balance of young competitive swimmers?

Abstract

During the repeated execution of the swimming strokes, the shoulder adductor and internal rotator muscles have a tendency to become proportionally stronger when compared to their antagonist group. This can lead to muscle imbalances. The aim of this study was to examine the effects of a compensatory training programme on the strength and balance of shoulder rotator muscles in young swimmers. A randomized controlled trial design was used. Forty male swimmers took part in the study and were randomly divided into two groups: an experimental group (n?=?20) and a training group (n?=?20). A control group (n?=?16) of young sedentary male students was also evaluated. The experimental group subjects participated in a 16-week shoulder-strength programme with Thera-Band^® elastic bands; the training group was restricted to aquatic training. Peak torque of shoulder internal rotator and external rotator (ER) was measured at baseline and after 16 weeks. Concentric action at 1.04?rad?s^?1 (3 reps) and 3.14?rad?s^?1 (20 reps) was measured using an isokinetic dynamometer. The strength-training programme led to an improvement of the ER strength and shoulder rotator balance in the experimental group (data from both shoulders at 1.04?rad?s^?1). Moreover, concentric action at 3.14?rad?s^?1 presented significant differences only for the dominant shoulder. Findings suggest that the prescribed shoulder-strengthening exercises could be a useful training option for young competitive swimmers. They can produce an increase in absolute strength values and greater muscle balance in shoulder rotators.     

虚拟应急演练系统的设计与实现

虚拟应急演练系统基于Torque3D游戏引擎开发,以应急预案为蓝本,以灾害伤害模型为理论依据,实现了灾害场景设置、事件注入、事件接报、事件分析研判、决策标绘、演练执行、演练总结等一系列应急演练流程。该系统能够体现应急预案的处置流程,训练各不同部门在应急处置过程中协作能力,检验各相关人员对预案实施的执行能力。     

扭矩对于煤矿锚杆支护结构强度的影响

分析了现有锚杆力学传递机制的研究特点,指出煤矿拉伸型锚杆的受力特征,并通过理论计算表明矿用拉伸型锚杆支护结构的强度受到轴力和扭矩的共同影响,附加扭矩降低了锚杆支护结构的强度。由此总结出改进预紧力施加方法应该遵循的原则是直接张拉锚杆,避免提高支护成本和安装工艺复杂化。     

中国国家蹦床队运动员髋、膝关节屈伸肌群力量特征分析

新规则的出台,弹性更大弹网的出现,都对蹦床运动项目体能和技术产生革命性的影响,针对这一新特点必须加快跟进研究。2012年伦敦奥运会越来越近,中国国家蹦床队能否续写2008年北京奥运会赛场上的辉煌,科研保障必须跟上。研究运用Isomed2000等速力量测试与训练系统,对国家蹦床队10名队员左右腿髋、膝关节屈伸肌群肌力的等速测试,通过峰力矩找出国家蹦床队员髋、膝关节肌肉群肌力的整体情况和个体差异,为未来的训练提供依据。研究结果表明:国家蹦床队队员整体髋、膝关节肌力发展的个体差异显著;髋、膝关节左右腿同名肌群肌力比较均衡,个体具有一定的差异;膝关节屈伸肌群肌力比值严重偏低,不利于下肢的稳定性;运动员整体左腿力量弱于右腿,需要在训练中引起重视。     

排球运动员下肢起跳肌群等速测试的研究

用Biodex等速测力系统对排球运动员进行了下肢3关节肌的力量测试,获得了在两种不同速度下的等动测试数据,并把所得数据与运动学拍摄的结果相结合进行了分析研究.结果显示运动员的弹跳能力与下肢起跳肌群等速测试的结果较为一致;下肢髋关节和膝关节起跳肌群肌肉力量和肌肉耐力对起跳能力有较大影响;功疲劳度可以作为评价运动员肌肉耐力素质的有效指标.