Validity of wearable activity monitors for tracking steps and estimating energy expenditure during a graded maximal treadmill test

The purpose of this study was to assess the accuracy of energy expenditure (EE) estimation and step tracking abilities of six activity monitors (AMs) in relation to indirect calorimetry and hand counted steps and assess the accuracy of the AMs between high and low fit individuals in order to assess the impact of exercise intensity. Fifty participants wore the Basis watch, Fitbit Flex, Polar FT7, Jawbone, Omron pedometer, and Actigraph during a maximal graded treadmill test. Correlations, intra-class correlations, and t-tests determined accuracy and agreement between AMs and criterions. The results indicate that the Omron, Fitbit, and Actigraph were accurate for measuring steps while the Basis and Jawbone significantly underestimated steps. All AMs were significantly correlated with indirect calorimetry, however, no devices showed agreement (p < .05). When comparing low and high fit groups, correlations between AMs and indirect calorimetry improved for the low fit group, suggesting AMs may be better at measuring EE at lower intensity exercise.     

Analysis of elbow muscle strength parameters in Brazilian jiu-jitsu practitioners

Upper-body dynamic and isometric maximum strength are essential components for success in Brazilian jiu-jitsu (BJJ). This study was aimed at analysing strength parameters in the elbow flexor and extensor muscles of BJJ practitioners. Participants (n = 28) performed maximum isometric contractions of elbow flexors and extensors to determine peak torque (PT), rate of force development (RFD), and the torque–angle (T–A) relationship at elbow angles of 45°, 60°, 75°, 90°, 105°, and 120°. Additionally, concentric and eccentric PTs were measured at 1.04 rad·s^-1. Student t-test and ANOVA were performed using α = 0.05. Elbow flexors were stronger isometrically (P < 0.001, ES = 1.23) but weaker concentrically (P < 0.05, ES = 0.54) than extensor muscles, possibly because of the extensive grip disputes and pushing of opponents in BJJ. The T–A relationship had an inverted “U”-shape. Torque differences across elbow angles were moderate (ES = 0.62) for the extensor and large (ES = 0.92) for the flexor muscles. Isometric torque was greatest for elbow angles of 105° and 75° and smallest for 45° and 120° for extensor and flexor muscles, respectively. Elbow flexors had a greater RFD than extensors, regardless of elbow angle. The present study provides comprehensive results for elbow muscle strength in BJJ practitioners.     

Kinetic analysis of the lower limbs in baseball tee batting

The purpose of this study was to investigate effects of the ground reaction forces on the rotation of the body as a whole and on the joint torques of the lower limbs associated with trunk and pelvic rotation in baseball tee batting. A total of 22 male collegiate baseball players participated in this study. Three-dimensional coordinate data were acquired by a motion capture system (250 Hz), and ground reaction forces of both legs were measured with three force platforms (1,000 Hz). Kinetic data were used to calculate the moment about the vertical axis through the body’s centre of mass resulting from ground reaction forces, as well as to calculate the torque and mechanical work in the lower limb joints. The lateral/medial ground reaction force generated by both legs resulted in the large whole body moment about its vertical axis. The joint torques of flexion/extension of both hips, adduction of the stride hip and extension of the stride knee produced significantly larger mechanical work than did the other joint torques. To obtain high bat-head speed, the batter should push both legs in the lateral/medial direction by utilising both hips and stride knee torques so as to increase the whole body rotation.     

浅谈中长跑大运动量训练结束后的恢复

恢复训练在现代中长跑训练体系中占有重要的地位,同时也是运动训练中的一个重要组成部分。现代中长跑训练为了使运动员获得较好的成绩,都必须从事大运动量训练,伴随而来的就是疲劳的产生。如何才能使运动员的疲劳更快的消除呢？因为训练结束后恢复得好和坏与运动员的成绩息息相关,目前运动成绩的竞争,也就是大运动量训练结束后恢复效果的竞争,谁大运动量训练结束后恢复抓的好抓的紧,就可能成为明天赛场上的获胜者。     

最大速度对提高100 m成绩作用的再认识

越来越多的研究表明,最大速度是提高100m成绩的关键。然而,我国的100m成绩并未随着运动员最大速度的提高而得到相应的显著提高。为此,运用影片解析等方法对我国和世界优秀女子短跑运动员100m的相关数据进行对比分析,结果表明,最大速度值本身并不能完全代表它对100m所起的作用,我国100m成绩的提高有赖于短跑所需的各种速度能力的综合提高,而其中最为关键则是加速跑的质量（加速节奏和能达到的速度最高值）。     

Dynamic simulation and optimal control strategy for a parallel hybrid hydraulic excavator

The primary focus of this study is to investigate the control strategies of a hybrid system used in hydraulic excavators. First, the structure and evaluation target of hybrid hydraulic excavators are analyzed. Then the dynamic system model including batteries, motor and engine is built as the simulation environment to obtain control results. A so-called multi-work-point dynamic control strategy, which has both closed-loop speed PI （proportion integral） control and direct torque control, is proposed and studied in the simulation model. Simulation results indicate that the hybrid system with this strategy can meet the power demand and achieve better system stability and higher fuel efficiency.     

跳远运动员下肢关节振动力量训练效果的比较研究

对10名跳远专项二级运动员8周系统的振动力量训练研究表明:在刺激频率为30～35 Hz、加速度25～30m/s2条件下,实验组(I组)和对照组(Ⅱ组)髋、膝、踝关节的伸屈肌群最大功都有不同程度提高,其中I组髋关节伸屈肌、膝、踝关节的屈肌最大功增长幅度比Ⅱ组大,屈肌最大功增长幅度比伸肌大,而且屈肌的最大功要比实验前呈现显著性增长;I组髋关节伸屈肌、膝关节屈肌、踝关节伸肌相对峰力矩的增值幅度比Ⅱ组大,而髋、膝、踝三个关节屈肌相对峰力矩增长幅度相对较小.髋、膝、踝关节肌力增长情况表明:髋关节前4周增长幅度较低,后4周增长幅度较高,呈现出明显的"先低后高"变化特征;而膝、踝关节前4周增长幅度较高,后4周提高幅度降低,呈现出明显的"先高后低"变化特征.     

不同强度下健美操运动对女大学生心肺功能影响的实验研究

为探讨特定负荷强度健美操运动对女大学生心肺功能的影响,将我校体育专业健美操专修班女生分成实验组和对照组,以不同强度训练一年,利用德国产Cortex 3B型号的心肺功能仪测试其训练前后的心肺功能指标,并分析指标数据的前后变化特点.实验结果表明:无氧阈强度下健美操运动可明显改善大学生的心率、最大通气量、摄氧量、氧脉搏、等心肺功能指标.研究认为,在无氧阈强度下的健美操运动更能促进女大学生心肺功能的提高.     

论以人为本与唯物史观的统一

马克思以前的哲学家们在关注和探讨人的问题过程中,已确立以人为本的思想.马克思和恩格斯继承了西方哲学关注人及其生存境遇的哲学思维传统,并赋予人本思想新的内涵.唯物史观的创立,除了当时社会历史提供的客观条件之外,从马克思和恩格斯的个人条件看,也是他们的人本思想发展的必然.从唯物史观的基本内容和历史使命来看,以人为本是唯物史观的最高价值原则.