对广义二力平衡原理的探讨     

赵山 《周口师范学院学报》1999,(5)

本文把二力平衡原理从静力学到动力学推广到完整系统和非完整系统．认为所有经典力学原理都具有“相似性”,且阐述同一力学规律时,它们是“等价”的,其广义力可相互推导．  相似文献   

酶促反应动力学米氏常数的意义及在体育中的应用     

Hou Guangbin 《湘南学院学报》1998,(2)

本文探讨米氏常数对酶研究的重要意义及酶促动力学在体育教学、训练中的应用  相似文献   

French research into the didactics and technology of physical activities and sportes: An expanding new field     

David  Bernard  Bouthier  Daniel  Marsenach  Jackie  Durey  Alain 《Instructional Science》1999,27(1-2):147-163

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配合物K3[Al（C2O4）3]·3H2O的热分解反应及其动力学研究     

何飞刚 《延安教育学院学报》2009,23(1):101-103

采用TG—DSC方法研究了配合物K3[Al（C2O4）3]·3H2O的热分解反应过程,对其进行了动力学计算。由Friedman、Ozawa—Flynn—Wall、ASTME698三种方法得出峰温时的活化能值与指前因子值。应用Achar方法计算拟舍得到了最佳的机理函数。  相似文献   

Kinetic and kinematic analysis of stamping impacts during simulated rucking in rugby union     

Bodil Y Oudshoorn  Heather F Driscoll  Marcus Dunn  David James 《Journal of sports sciences》2018,36(8):914-919

Laceration injuries account for up to 23% of injuries in rugby union. They are frequently caused by studded footwear as a result of a player stamping onto another player during the ruck. Little is known about the kinetics and kinematics of rugby stamping impacts; current test methods assessing laceration injury risk of stud designs therefore lack informed test parameters. In this study, twelve participants stamped on an anthropomorphic test device in a one-on-one simulated ruck setting. Velocity and inclination angle of the foot prior to impact was determined from high-speed video footage. Total stamping force and individual stud force were measured using pressure sensors. Mean foot inbound velocity was 4.3 m ? s^?1 (range 2.1–6.3 m ? s^?1). Mean peak total force was 1246 N and mean peak stud force was 214 N. The total mean effective mass during stamping was 6.6 kg (range: 1.6–13.5 kg) and stud effective mass was 1.2 kg (range: 0.5–2.9 kg). These results provide representative test parameters for mechanical test devices designed to assess laceration injury risk of studded footwear for rugby union.  相似文献   

Comparative study on activating fly ash by quick lime and slaked lime: effects and kinetics     

WEI Ying-chun  WANG Zhi  QIAN Jue-shi 《重庆大学学报(英文版)》2009,8(3):175-180

Lime, which is a frequently used activating agent of fly ash （FA）, has two main states： slaked lime and quick lime. We studied the effects of slaked lime and quick lime on activating FA, and discussed their kinetics. The results show that slaked lime is more beneficial for activating FA than quick lime given the condition of equivalent CaO amount. The use of slaked lime has superiority in technology and economy on activating FA. Theoretical analysis revealed that the kinetic constant of the activation reaction using slaked lime is higher than using quick lime, credited to the better volume stability and fineness, and smaller water demand of slaked lime.  相似文献   

国家优秀女子速滑运动员直道滑行中下肢功率情况分析     

王新  夏娇阳 《首都体育学院学报》2012,24(4):381-384

为了有效评价运动员下肢各环节在蹬冰过程中的贡献情况,借助爱捷三维录像解析系统和CY-BEXNORM等动测试装置获得国家健将级女子速滑运动员的运动学和动力学数据,并采用牛顿差值计算方法计算出与实际运动学数据相对应的关节力矩,在此基础上计算出下肢各环节在蹬冰时功率输出值。研究结果表明:髋关节在单支撑阶段适当伸展,有利于增加整个蹬冰阶段的大腿功率输出;高速度、大角度伸膝肌群肌力差,引起两人小腿峰值功率过早出现,减少双支撑蹬冰阶段功率输出;踝关节肌力不足,刻意展踝,加重了伸小腿肌力不足现象,减少小腿在整个蹬冰过程中的作用。  相似文献   

Effect of movement speed on trunk and hip exercise performance     

《European Journal of Sport Science》2013,13(6):547-555

Abstract

The influence of speed on trunk exercise technique is poorly understood. The aim of this study was to analyse the effect of movement speed on the kinematics and kinetics of curl-up, sit-up and leg raising/lowering exercises. Seventeen healthy, recreationally trained individuals (13 females and 4 males) volunteered to participate in this study. Four different exercise cadences were analysed: 1 repetition/4 s, 1 repetition/2 s, 1 repetition/1.5 s and 1 repetition/1 s. The exercises were executed on a force plate and recorded by three cameras to conduct a 3D photogrammetric analysis. The cephalo-caudal displacement of the centre of pressure and range of motion (ROM) of six joints describing the trunk and hip movements were measured. As sit-up and curl-up speed increased, hip and knee ROM increased. Dorsal-lumbar and upper trunk ROM increased with speed in the curl-up. Faster cadence in the sit-up exercise had minimal effect on trunk ROM: only the upper trunk ROM decreased significantly. In the leg raising/lowering exercise there was a decrease in the pelvic tilt and hip ROM, and increased knee flexion ROM. During higher speed exercises, participants modified their technique to maintain the cadence. Thus, professionals would do well to monitor and control participants' technique during high-speed exercises to maintain performance specificity. Results also suggest division of speed into two cadence categories, to be used as a reference for prescribing exercise speed based on preferred outcome goals.  相似文献   

Effects of load on ground reaction force and lower limb kinematics during concentric squats     

Eleftherios Kellis  Fotini Arambatzi  Christos Papadopoulos 《Journal of sports sciences》2013,31(10):1045-1055

The purpose of this study was to examine the effects of external load on vertical ground reaction force, and linear and angular kinematics, during squats. Eight males aged 22.1?±?0.8 years performed maximal concentric squats using loads ranging from 7 to 70% of one-repetition maximum on a force plate while linear barbell velocity and the angular kinematics of the hip, knee and ankle were recorded. Maximum, average and angle-specific values were recorded. The ground reaction force ranged from 1.67?±?0.20 to 3.21?±?0.29 times body weight and increased significantly as external load increased (P?<?0.05). Bar linear velocity ranged from 0.54?±?0.11 to 2.50?±?0.50?m?·?s^?1 and decreased significantly with increasing external load (P?<?0.05). Hip, knee and ankle angles at maximum ground reaction force were affected by external load (P?<?0.05). The force?–?barbell velocity curves were fitted using linear models with coefficients (r ²) ranging from 0.59 to 0.96. The results suggest that maximal force exertion during squat exercises is not achieved at the same position of the lower body as external load is increased. In contrast, joint velocity coordination does not change as load is increased. The force?–?velocity relationship was linear and independent from the set of data used for its determination.  相似文献   

Contraction force specificity and its relationship to functional performance     

Nigel Harris  John Cronin  Justin Keogh 《Journal of sports sciences》2013,31(2):201-212

Abstract

Best practice for improving strength and power through resistance strength training has been the subject of much research and subsequent conjecture. Much of the conjecture can be attributed to methodological discrepancies. The type of dynamometry used in testing, the training experience of research participants, the specific technique employed in a lift, and the methods of collection and calculation all impact on the final variables of interest. This review examines contraction force specificity by first addressing the methodological issues surrounding our interpretation of the results. Then we address the kinematics and kinetics associated with single and multiple repetitions in relation to the development of strength, power, and functional performance. This discussion provides the delimitations for analysis of subsequent training studies. Finally, recommendations are formulated with the aim of assisting assessment and training practice as well as providing directions for future research. The results of this review suggest that the enhancements in performance resulting from resistance training are context specific in experienced resistance-trained participants. Thus, specific conditioning could be required to achieve improvements in functional performance in this group.  相似文献