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The aim of this study was to evaluate the effect of varying knee angle (120° and 90°) on the external validity of an isometric leg press test with reference to vertical jump performance. Isometric peak force (PF 120 and PF 90 ), rate of force development (RFD 120 and RFD 90 ), and maximum height reached with a squat jump and counter-movement jump were measured in 14 males. Although RFD 120 was significantly correlated with squat jump and counter-movement jump performance ( r = 0.71 and 0.69), and the correlations with PF 120 approached statistical significance ( r = 0.53 and 0.50), neither PF 90 nor RFD 90 was significantly related to vertical jump performance. Furthermore, although both RFD 120 and PF 120 were significantly different between the best five and the worst five jumpers, RFD 90 and PF 90 did not differentiate between individuals' vertical jump performance. We conclude that the choice of joint angle affects the external validity of isometric strength testing. Based on our results, we recommend accurate control of biomechanical specificity and assessment at different angles to find the position at which isometric strength testing is most comfortable. 相似文献
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目的：：探讨棒球投手运动学与等速肌力参数间关联关系，并比较不同类型投手各类参数的差异性。方法：采用德国ISOMED2000等速肌力测试系统及三台高速摄像机获取相关参数。结果：( a)肩关节外、内旋峰力矩及屈、伸峰力矩两个比值高度相关，两者均与挥肘速度、棒球出手及触垒速度高度正相关；( b)与“非衡型”棒球投手相比，“均衡型”投手在许多关键参数上存有显著差异，表现为投球动作总时间、提膝时间、伸踏时间及动作加速时间显著变短；肘关节屈伸幅度、棒球出手等及触垒速度则显著增大；( c)挥肘速度与肩关节最大外展角存有显著正相关，而与投球动作总时间呈负相关；动作加速时间与肩关节最大外展角成负相关，却与躯干扭转角成正相关；( d)棒球出手及触垒速度均与肩关节最大外展角等呈显著正相关。结论：目前我国大学生优秀棒球投手与国外同级别投手相比，在众多运动学测试指标上存有显著差距，而投掷臂肌力发展不均衡是问题的关键所在。 相似文献
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刘良瑞 《黄冈职业技术学院学报》2010,12(5):24-27,46
本文介绍了使用AutoCAD2010软件对正等轴测图绘制文字和标注尺寸的方法与技巧。 相似文献
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Anderson Souza Oliveira Rogério Bulhões Corvino Fabrizio Caputo Per Aagaard 《European Journal of Sport Science》2016,16(2):199-205
This study examined whether short-term maximal resistance training employing fast-velocity eccentric knee extensor actions would induce improvements in maximal isometric torque and rate of force development (RFD) at early (<100 ms) and late phases (>100 ms) of rising torque. Twenty healthy men were assigned to two experimental groups: eccentric resistance training (TG) or control (CG). Participants on the TG trained three days a week for a total of eight weeks. Training consisted of maximal unilateral eccentric knee extensors actions performed at 180°s-1. Maximal isometric knee extensor torque (MVC) and incremental RFD in successive 50 ms time-windows from the onset contraction were analysed in absolute terms (RFDINC) or when normalised relative to MVC (RFDREL). After eight weeks, TG demonstrated increases in MVC (28%), RFDINC (0–50 ms: 30%; 50–100 ms: 31%) and RFDREL (0–50 ms: 29%; 50–100 ms: 32%). Moreover, no changes in the late phase of incremental RFD were observed in TG. No changes were found in the CG. In summary, we have demonstrated, in active individuals, that a short period of resistance training performed with eccentric fast-velocity isokinetic muscle contractions is able to enhance RFDINC and RFDREL obtained at the early phase of rising joint torque. 相似文献
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《European Journal of Sport Science》2013,13(2):95-103
Abstract The main aim of this study was to compare the reliability of percutaneous electrical stimulation over the muscle (MES) and electrical stimulation over the nerve (NES) to assess quadriceps muscle voluntary activation and muscle contractile properties. A secondary aim was to determine whether MES detects the fatigue induced by prolonged exercise in the heat. For the first purpose, eight participants performed on three non-consecutive days: quadriceps maximal voluntary contractions (MVC) with superimposed electrical stimulation to assess voluntary activation, and electrically evoked contractions to assess peak force (PEVO), using NES (ball-shaped cathode) or MES (adhesive electrodes). For the second purpose, the same participants pedalled for 2 h at 60% VO2max in a 36°C environment. Quadriceps maximal voluntary contractions, voluntary activation, and PEVO were measured before and just after the completion of exercise using MES. Voluntary activation assessed with MES presented lower intra-day (1.3±0.2 vs. 2.5±0.5%) and inter-day (1.7±0.3 vs. 2.9 ±0.4%) coefficients of variation than with NES. PEVO had lower intra-day and inter-day coefficients of variation (5.6±1.0 vs. 17.0±3.3%) and higher intraclass correlation values (ICC 0.95 vs. 0.85) when using MES than with NES either when stimulating at 20 or 80 Hz. Prolonged exercise in the heat reduced MVC (11±2%) and quadriceps muscle voluntary activation (5.2±0.5%) from pre-exercise values (P<0.05), as previously found. PEVO was unaffected by exercise in the heat. In conclusion, MES is more reliable than NES to assess quadriceps muscle voluntary activation and PEVO. In addition, MES readily detects the reduction in voluntary activation induced by prolonged exercise in the heat. 相似文献
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Malachy P. McHugh Declan A. J. Connolly Roger G. Eston Gilbert W. Gleim 《Journal of sports sciences》2013,31(3):163-172
Surface electromyographic (EMG) signals were recorded from the hamstring muscles during six sets of submaximal isokinetic (2.6 rad s -1 ) eccentric (11 men, 9 women) or concentric (6 men, 4 women) contractions. The EMG per unit torque increased during eccentric (P < 0.01) but not during concentric exercise. Similarly, the median frequency increased during eccentric (P < 0.01) but not during concentric exercise. The EMG per unit torque was lower for submaximal eccentric than maximum isometric contractions (P < 0.001), and lower for submaximal concentric than maximum isometric contractions (P < 0.01). The EMG per unit torque was lower for eccentric than concentric contractions (P < 0.05). The median frequency was higher for submaximal eccentric than maximum isometric contractions (P < 0.001); it was similar, however, between submaximal concentric and maximum isometric contractions (P = 0.07). Eccentric exercise resulted in significant isometric strength loss (P < 0.01), pain (P < 0.01) and muscle tenderness (P < 0.05). The greatest strength loss was seen 1 day after eccentric exercise, while the most severe pain and muscle tenderness occurred 2 days after eccentric exercise. A lower EMG per unit torque is consistent with the selective recruitment of a small number of motor units during eccentric exercise. A higher median frequency during eccentric contractions may be explained by selective recruitment of fast-twitch motor units. The present results are consistent with the theory that muscle damage results from excessive stress on a small number of active fibres during eccentric contractions. 相似文献
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《European Journal of Sport Science》2013,13(1):27-33
Abstract In this study, we examined indirect markers of muscle damage and muscle soreness following a 50-km cross-country ski race completed in 2 h and 57 min to 5 h and 9 min by 11 moderately trained male university students. Maximal strength of the knee extensors, several blood markers of muscle damage and inflammation, and muscle soreness (visual analog scale: 0 = “no pain”, 50 mm = “unbearably painful”) were measured one day before, immediately after, and 24, 48, 72, and 144 h after the race. Changes in the measures over time were analysed using one-way repeated-measures analysis of variance and a Fisher's post-hoc test. Maximal strength of the knee extensors decreased significantly (P<0.05) immediately after the race (mean ?27%, s=6), but returned to pre-exercise values within 24 h of the race. All blood markers increased significantly (P<0.05) following the race, peaking either immediately (lactate dehydrogenase: 253.7 IU · l?1, s=13.3; myoglobin: 476.4 ng · ml?1, s=85.5) or 24 h after the race (creatine kinase: 848.0 IU · l?1, s=151.9; glumatic oxaloacetic transaminase: 44.3 IU · l?1, s=4.2; aldolase: 10.0 IU · l?1, s=1.3; C-reactive protein: 0.36 IU · l?1, s=0.08). Muscle soreness developed in the leg, arm, shoulder, back, and abdomen muscles immediately after the race (10–30 mm), but decreased after 24 h (<15 mm), and disappeared 48 h after the race. These results suggest that muscle damage induced by a 50-km cross-country ski race is mild and recovery from the race does not take long. 相似文献