Fatigue effects upon sticking region and electromyography in a six-repetition maximum bench press     

Roland van den Tillaar  Atle Hole Saeterbakken 《Journal of sports sciences》2013,31(16):1823-1830

Abstract

The aim of the study was to examine the sticking region and concomitant neuromuscular activation of the prime movers during six-repetition maximum (RM) bench pressing. We hypothesised that both peak velocities would decrease and that the electromyography (EMG) of the prime movers (deltoid, major pectoralis and triceps) would increase during the pre-sticking and sticking region during the six repetitions due to fatigue. Thirteen resistance-trained males (age 22.8 ± 2.2 years, stature 1.82 ± 0.06 m, body mass 83.4 ± 7.6 kg) performed 6-RM bench presses. Barbell kinematics and EMG activity of pectoralis major, deltoid anterior, and triceps brachii during the pre-, sticking and post-sticking region of each repetition in a 6-RM bench press were analysed. For both the sticking as the post-sticking region, the time increased significantly from the first to the sixth repetition. Vertical barbell height at the start of sticking region was lower, while the height at the end of the sticking region and post-sticking region did not change during the six repetitions. It was concluded that in 6-RM bench pressing performance, the sticking region is a poor mechanical force region due to the unchanged barbell height at the end of the sticking region. Furthermore, when fatigue occurs, the pectoralis and the deltoid muscles are responsible for surpassing the sticking region as indicated by their increased activity during the pre- and sticking region during the six-repetitions bench press.  相似文献   

The influence of cricket fast bowlers’ front leg technique on peak ground reaction forces     

Peter Worthington  Craig Ranson 《Journal of sports sciences》2013,31(4):434-441

Abstract

High ground reaction forces during the front foot contact phase of the bowling action are believed to be a major contributor to the high prevalence of lumbar stress fractures in fast bowlers. This study aimed to investigate the influence of front leg technique on peak ground reaction forces during the delivery stride. Three-dimensional kinematic data and ground reaction forces during the front foot contact phase were captured for 20 elite male fast bowlers. Eight kinematic parameters were determined for each performance, describing run-up speed and front leg technique, in addition to peak force and time to peak force in the vertical and horizontal directions. There were substantial variations between bowlers in both peak forces (vertical 6.7 ± 1.4 body weights; horizontal (braking) 4.5 ± 0.8 body weights) and times to peak force (vertical 0.03 ± 0.01 s; horizontal 0.03 ± 0.01 s). These differences were found to be linked to the orientation of the front leg at the instant of front foot contact. In particular, a larger plant angle and a heel strike technique were associated with lower peak forces and longer times to peak force during the front foot contact phase, which may help reduce the likelihood of lower back injuries.  相似文献   

The respiratory time and flow profile at volitional exercise termination     

Jamie Kift 《Journal of sports sciences》2013,31(14):1599-1606

Abstract

In this study, we examine the effect of exercise on the time and flow characteristics of the respiratory cycle profile at the point of volitional exercise termination. Eight males (mean age 29 years, s = 10; body mass 74 kg, s = 7; height 1.75 m, s = 0.04) undertook a cycle test to volitional exhaustion on a cycle ergometer, which allowed peak oxygen uptake ([Vdot]O_2peak) to be measured (mean 51 ml · kg^?1 · min^?1, s = 7). At a later date, two sub-maximal tests to volitional exhaustion were completed in a random order at 76% (s = 6) and 86%[Vdot]O_2peak (s = 7). As expected, the magnitude of the respiratory flow and time characteristics varied with the three exercise intensities, as did the point of exercise termination and terminal ventilation rates, which varied from 7 to 27 min and 112 to 132 litres · min^?1 respectively. More importantly, however, at exercise termination some of the characteristics were similar, particularly the breathing frequency (at termination 49 breaths · min^?1), the ratio between inspiration and total breath time (0.5), and the later occurrence of peak inspiratory flow (0.24 – 0.48 s). The coincident unity of these time and flow profile characteristics at exercise termination illustrates how the integration of timing and flow during breathing influence exercise capacity in non-elite athletes.  相似文献   

Muscle fatigue induced by exercise simulating the work rate of competitive soccer     

N Rahnama  T Reilly  A Lees  P Graham-Smith 《Journal of sports sciences》2013,31(11):933-942

Fatigue represents a reduction in the capability of muscle to generate force. The aim of the present study was to establish the effects of exercise that simulates the work rate of competitive soccer players on the strength of the knee extensors and knee flexors. Thirteen amateur soccer players (age 23.3±3.9 years, height 1.78±0.05?m, body mass 74.8±3.6?kg; mean±s) were tested during the 2000–2001 soccer season. Muscle strength of the quadriceps and hamstrings was measured on an isokinetic dynamometer. A 90?min soccer-specific intermittent exercise protocol, incorporating a 15?min half-time intermission, was developed to provide fatiguing exercise corresponding in work rate to a game of soccer. The exercise protocol, performed on a programmable motorized treadmill, consisted of the different intensities observed during soccer match-play (e.g. walking, jogging, running, sprinting). Muscle strength was assessed before exercise, at half-time and immediately after exercise. A repeated-measures analysis of variance showed significant reductions (P?<0.001) in peak torque for both the quadriceps and hamstrings at all angular velocities (concentric: 1.05, 2.09, 5.23 rad?·?s^?1; eccentric: 2.09 rad?·?s^?1). The peak torque of the knee extensors (KE) and knee flexors (KF) was greater before exercise [KE: 232±37, 182±34, 129±27, 219±41?N?·?m at 1.05, 2.09 and 5.23 rad?·?s^?1 (concentric) and 2.09 rad?·?s^?1 (eccentric), respectively; KF: 126±20, 112±19, 101±16, 137±23?N?·?m] than at half-time (KE: 209±45, 177±35, 125±36, 214±43?N?·?m; KF: 114±31, 102±20, 92±15, 125±25?N?·?m) and greater at half-time than after exercise (KE: 196±43, 167±35, 118±24, 204±43?N?·?m; KF: 104±25, 95±21, 87±13, 114±27?N?·?m). For the hamstrings?:?quadriceps ratio, significant changes were found (P?<0.05) for both legs, the ratio being greater before than after exercise. For fast?:?slow speed and left?:?right ratios, no significant changes were found. We conclude that there is a progressive reduction in muscle strength that applies across a range of functional characteristics during exercise that mimics the work rate in soccer.  相似文献   

THz-TDS和FTIR对云冈石窟岩芯的光谱分析     

杨成全  孟田华  卢玉和  任建光 《雁北师范学院学报》2013,(4):13-16

分别利用太赫兹时域光谱系统（THz-TDS）和傅里叶变换红外光谱仪（FTIR）,对由钻孔取芯机所取岩芯上选取的6个不同深度样品进行了测试。结果表明：随着样品深度的增加,在太赫兹波段,吸收系数和透射系数变化不明显,但折射率则逐渐降低;在红外波段,样品所含盐类逐渐减少,而CaCO3和SiO2的含量则逐渐增大,说明盐类物质是由外部环境污染而来,内部岩石则尚未被污染。  相似文献   

我国优秀短距离速滑运动员弯道滑冰腿部肌电特征研究     

吴新炎  陈月亮 《北京体育大学学报》2014,37(10):77-82

摘要：目的：通过分析短距离速滑运动员弯道单步周期腿部肌电特征,探讨弯道单步周期腿部肌肉动作和协调模式,发现腿部力量训练可能存在的问题。方法：采集运动员第一弯道2-6连续5次单步周期肌电图,原始肌电图进行全波整流处理,再进行均化处理。结论：1）单步周期收腿阶段大小腿折叠可能是由蹬伸动作的后效应引起的随势动作,踝关节在右单步周期收腿阶段背屈,落腿阶段拓屈,左单步周期收腿阶段和落腿阶段前期背屈,落腿阶段后期拓屈;2）左单步周期重心转移阶段腓肠肌表现出与胫骨前肌共激活,蹬冰阶段胫骨前肌表现出与腓肠肌共激活,但激活程度逐渐降低,直至消失。蹬冰期股四头肌和股后肌群表现共激活协调模式,左单步周期协调性更高;3）在实践训练过程中对胫骨前肌、股直肌和臀大肌存在认识不足的问题。  相似文献   

三维地震勘探技术在煤矿采空区探测中的应用   总被引：1，自引：0，他引：1  

霍军鹏  周竹峰  王万合 《黑龙江科技信息》2012,(14):15-16

本文以三维地震勘探技术在陕北韩家湾煤矿的应用为基础,通过对小煤窑采空区和煤矿综采形成的采空区特征认识、总结,结合地震剖面和提取的地震波最大振幅属性,解释了采空区的分布范围,解释结果与矿方钻探资料对比,吻合较好,说明该方法适用于煤矿采空区的探测,且效果较好。  相似文献   

基于MC1496平衡调幅实验电路的分析与改进     

李红 《中国现代教育装备》2010,(9):42-44

文章介绍了基于MC1496平衡调幅实验电路的工作原理和实验方法,推导了调制度理论值的计算公式,对实验结果调制度船。实验值与理论值的误差进行了分析,指出了造成误差的原因,提出了减小误差的方法,将基于MC1496平衡调幅实验电路的耦合电容C3的电容值从原来的10uF改变成33uF。本文给出了C3=10uF和C3=33uF时的实验结果。实验结果表明,调制度ma实测值与理论值的误差大为减小,调制度ma的实验精度大为提高。  相似文献   

张爱玲小说的颠峰与末路     

袁良骏 《南通师范学院学报》2010,(4):81-89

张爱玲以中国传统小说特别《红楼梦》为底色,广收博采,中体西用,兼收并蓄,做到了艺术上的中体西用、中西合璧。张爱玲是一个中西文化功底都很扎实的富有现代色彩的作家。张家玲早期以《传奇》为代表的十九篇小说堪称其创作颠峰。这批小说在为人生、为社会的主流文学基础上,做出了新的开拓和贡献。其善写婚恋中男女的心理变化,大大丰富了现代文学的艺术手段;善写人性异化和心理变态,在现代文学中更是独树一帜。这批小说意象丰富,文字优美,耐人咀嚼,具有参差对照的艺术风格和苍凉美,以及中体西用、中西合璧的艺术取向。张爱玲晚年创作力衰退,其小说创作因滑波而走向末路,这除了因为抗战胜利之后政治环境的变化外,还要充分考虑到张爱玲赴美定居后的种种不利因素,首先是因为她远离祖国,举目无亲,连生存都成了问题,还谈何创作;其次是她无法融入美国社会,仅靠英文好,并不能写出切近社会生活的好作品;此外随着年龄的增长,俗务的缠身,张爱玲晚年创作力的衰退也符合自然规律,并不值得大惊小怪。  相似文献   

CFRP约束轴压预压混凝土的峰值应变预测     

李素娟 《唐山学院学报》2012,25(6):81-83

对CFRP约束预压混凝土的轴压性能试验进行研究,并对混凝土的峰值应变的影响因素进行分析。结果发现,对于CFRP约束预压混凝土,峰值应变的主要影响因素可归结为等效圆柱约束刚度Er,混凝土弹性模量Ec和预加轴压比B三个因素。参考已有峰值应变模型,结合参数分析,对已有峰值应变模型进行改进,提出CFRP约束轴压预压混凝土的峰值应变预测模型,为CFRP约束预压混凝土的应力-应变模型的参数确定提供计算方法。  相似文献