An accurate estimation of the horizontal acceleration of a rower’s centre of mass using inertial sensors: a validation

For a valid determination of a rower’s mechanical power output, the anterior–posterior (AP) acceleration of a rower’s centre of mass (CoM) is required. The current study was designed to evaluate the accuracy of the determination of this acceleration using a full-body inertial measurement units (IMUs) suit in combination with a mass distribution model. Three methods were evaluated. In the first two methods, IMU data were combined with either a subject-specific mass distribution or a standard mass distribution model for athletes. In the third method, a rower’s AP CoM acceleration was estimated using a single IMU placed at the pelvis.

Experienced rowers rowed on an ergometer that was placed on two force plates, while wearing a full-body IMUs suit. Correspondence values between AP CoM acceleration based on IMU data (the three methods) and AP CoM acceleration obtained from force plate data (reference) were calculated. Good correspondence was found between the reference AP CoM acceleration and the AP CoM accelerations determined using IMU data in combination with the subject-specific mass model and the standard mass model (intraclass correlation coefficients [ICC] >?0.988 and normalized root mean square errors [nRMSE]?3.81%). Correspondence was lower for the AP CoM accelerations determined using a single pelvis IMU (0.877?Based on these results, we recommend determining a rower’s AP CoM acceleration using IMUs in combination with the standard mass model. Finally, we conclude that accurate determination of a rower’s AP CoM acceleration is not possible on the basis of the pelvis acceleration only.     

Use of probabilistic and deterministic measures to identify unfavorable earthquake records

This study introduces measures to identify resonant （concentration of energy in a single or a few frequencies） or unfavorable earthquake ground motions. Probabilistic measures based on the entropy rate and the geometric properties of the power spectral density function （PSDF） of the ground acceleration are developed first. Subsequently, deterministic measures for the frequency content of the ground acceleration are also developed. These measures are then used for identifying resonance and criticality in stochastic earthquake models and 110 acceleration records measured at rock, stiff, medium and soft soil sites. The unfavorable earthquake record for a given structure is defined as the record having a narrow frequency content and dominant frequency close to the structure fundamental natural frequency. Accordingly, the measures developed in this study may provide a basis for selecting records that are capable of producing the highest structural response. Numerical verifications are provided on damage caused to structures by identified resonant records.     

心理拓展训练对大学生自我和人际关系的研究

运用心理拓展训练的手段,采用《容纳他人量表》、《田纳西自我概念量表》、《心理健康自评量表》对大学生进行团体心理训练。实验结果表明:心理拓展训练组的自我概念、对自我和他人的接纳及心理健康水平与另外两组相比,呈现积极变化。心理拓展训练组与健美操对照组都能对大学生的心理健康水平起到积极影响。     

基于加速度传感器的上肢爆发力训练研究

利用＂三轴加速度传感器＂对运动员不同负荷下的卧推训练进行数据采集,分析得知：不同人爆发力水平不同,不同人在相同负荷下的爆发力也不同;同一人在不同负荷下的爆发力不同,且都存在极值点;同一人在保证卧推质量的前提下,在相同负荷中完成的五次卧推中所表现出来的爆发力基本相同;同一人的爆发力水平具有固定性和阶段性;速度对爆发力起关键作用;活体肌肉的力速关系符合希尔方程规律,但实验中最大爆发力值的负荷在1RM的41%-45%之间,对应的速度和力量约为50%-53%最大速度和52%-55%最大力量。并提出相关建议。     

Velocity and acceleration before contact in the tackle during rugby union matches

Abstract

The velocity and acceleration at which the ball-carrier or tackler enters the tackle may contribute to winning the contest and prevailing injury free. Velocity and acceleration have been quantified in controlled settings, whereas in match-play it has been subjectively described. The purpose of this study was to determine the velocity and acceleration of the ball-carrier and tackler before contact during match-play in three competitions (Super 14, Varsity Cup, and Under-19 Currie Cup). Using a two-dimensional scaled version of the field, the velocity and acceleration of the ball-carrier and tackler were measured at every 0.1 s to contact for 0.5 s. For front-on tackles, a significant difference (P < 0.05) between the ball-carrier (4.6 ± 1 m · s^–1) and tackler (7.1 ± 3.5 m · s^–1) was found at the 0.5 s time to contact interval in the Varsity Cup. For side-on tackles, differences between the two opposing players were found at 0.5 s (ball-carrier: 4.6 ± 1.7 m · s^–1; tackler: 3.1 ± 1.2 m · s^–1) and 0.4 s (ball-carrier: 6.3 ± 2.3 m · s^–1; tackler: 3.7 ± 1.6 m · s^–1) at Under-19 level. After 0.4 s, no significant differences (P > 0.05) were evident. Also, the ball-carrier's velocity over the 0.5 s was relatively stable compared with that of the tackler. Results suggest that tacklers adjust their velocity to reach a suitable relative velocity before making contact with the ball-carrier.     

Acceleration patterns in the lower and upper trunk during running

Abstract

The purpose of the present study was to relate 3D acceleration patterns of the lower and upper trunk during running to running gait cycle, assess the validity of stride duration estimated from acceleration patterns, investigate speed-dependent changes in acceleration, and examine the test–retest reliability of these parameters. Thirteen healthy young men performed two running trials each on a treadmill and on land at three speeds (slow, preferred, and fast). The 3D accelerations were measured at the L3 spinous process (lower trunk) and the ensiform process (upper trunk) and synchronised with digital video data. The amplitude and root mean square of acceleration and stride duration were calculated and then analysed by three-way analysis of variance to test effects of running conditions, device location, and running speed. Bland-Altman analysis was used to evaluate the test–retest reliability. Marked changes in acceleration were observed in relation to foot strike during running. Stride durations calculated from the vertical accelerations were nearly equal to those estimated from video data. There were significant speed effects on all parameters, and the low test–retest reliability was confirmed in the anterior–posterior acceleration during treadmill running and the anterior–posterior acceleration at slow speed during treadmill and overground running.     

跳远助跑准确性教法的研究

跳远的完整技术包括助跑、起跳、腾空和落地4个连续的动作过程。4个环节中,无论哪个环节出现问题都会影响到跳远的成绩。研究影响助跑准确性的因素,探讨如何提高助跑准确性的教学方法。在教学中,着重强调跳远助跑准确性方法的教学,是提高跳远成绩的关键所在,从而使学生在短期内熟练掌握正确的助跑技术,并且能取得一定的效果。     

Technical Reliability Assessment of the Actigraph GT1M Accelerometer

The purpose of this study was to determine the reliability of the Actigraph GT1M (Pensacola, FL, USA) accelerometer activity count and step functions. Fifty GT1M accelerometers were initialized to collect simultaneous acceleration counts and steps data using 15-sec epochs. All reliability testing was completed using a mechanical shaker plate to perform six different test conditions in Experiment 1 and 18 test conditions in Experiment 2. The overall intra- and inter-instrument reliability of the GT1M was CV_intra = 2.9% and CV_inter = 3.5% for counts and CV_intra = 1.1% and CV_inter = 1.2% for steps. No batch effects were evident in the 50 GT1Ms. The Actigraph GT1M accelerometer demonstrated good reliability for measuring both counts and steps. However, the ability of the GT1M to consistently detect acceleration at a given acceleration and frequency condition varied widely. Future studies clarifying the filtering limitations and the threshold necessary to detect the occurrence of movement are warranted.     

Validity of an upper-body-mounted accelerometer to measure peak vertical and resultant force during running and change-of-direction tasks

This study assessed the validity of a tri-axial accelerometer worn on the upper body to estimate peak forces during running and change-of-direction tasks. Seventeen participants completed four different running and change-of-direction tasks (0°, 45°, 90°, and 180°; five trials per condition). Peak crania-caudal and resultant acceleration was converted to force and compared against peak force plate ground reaction force (GRF) in two formats (raw and smoothed). The resultant smoothed (10 Hz) and crania-caudal raw (except 180°) accelerometer values were not significantly different to resultant and vertical GRF for all running and change-of-direction tasks, respectively. Resultant accelerometer measures showed no to strong significant correlations (r = 0.00–0.76) and moderate to large measurement errors (coefficient of variation [CV] = 11.7–23.9%). Crania-caudal accelerometer measures showed small to moderate correlations (r = ? 0.26 to 0.39) and moderate to large measurement errors (CV = 15.0–20.6%). Accelerometers, within integrated micro-technology tracking devices and worn on the upper body, can provide a relative measure of peak impact force experienced during running and two change-of-direction tasks (45° and 90°) provided that resultant smoothed values are used.     

论教师的形象境界

教师的外在形象和内在形象的完善统一构成了独特的职业。在新的历史 时期,教师的外在形象连同他的社会价值被现凸现出来,教师的内在形象表现在自身的德才学识和身心素质。时代要求教师在完善自身形象的同时达到一定的学术境界,育人境界和职业道德境界。