密度对稻秸秆纤维板物理性能的影响   总被引：1，自引：0，他引：1  

朱云  申黎明 《茂名学院学报》2013,(4):53-55

密度与稻秸秆板的物理力学性能密切相关。研究表明,合理的剖面密度和平面密度分布对稻秸秆板的弹性模量、静曲强度、内结合强度、翘曲度等物理指标有积极的影响。在不同工艺条件和使用要求下,稻秸秆板的最佳密度点能够在相关正负效应间找到平衡点,进一步提升稻秸秆板在家具产业中的利用空间。  相似文献   

带电圆线圈静电场勒让德级数解的收敛速度     

江俊勤 《广东教育学院学报》2013,(5):46-50

通过绘制电势和电场强度的空间分布图,对均匀带电圆线圈的静电场勒让德级数解的收敛速度进行数值研究.结果表明:电场强度勒让德级数解的收敛十分缓慢,用此级数绘制出电场强度的空间分布图远不如直接用叠加原理快捷.  相似文献   

Prevalence and correlates of resistance training skill competence in adolescents     

Jordan J. Smith  Matthew DeMarco  Sarah G. Kennedy  Mark Kelson  Lisa M. Barnett  Avery D. Faigenbaum 《Journal of sports sciences》2018,36(11):1241-1249

The aim of this study is to examine the prevalence and correlates of adolescents’ resistance training (RT) skill competence. Participants were 548 adolescents (14.1 ± 0.5 years) from 16 schools in New South Wales, Australia. RT skills were assessed using the Resistance Training Skills Battery. Demographics, BMI, muscular fitness, perceived strength, RT self-efficacy, and motivation for RT were also assessed. The proportion demonstrating “competence” and “near competence” in each of the six RT skills were calculated and sex differences explored. Associations between the combined RT skill score and potential correlates were examined using multi-level linear mixed models. Overall, the prevalence of competence was low (range = 3.3% to 27.9%). Females outperformed males on the squat, lunge and overhead press, whereas males performed better on the push-up (p < .05). Significant associations were seen for a number of correlates, which largely differed by sex. Muscular fitness was moderately and positively associated with RT skills among both males (β = 0.34, 95%CIs = 0.23 to 0.46) and females (β = 0.36, 95%CIs = 0.23 to 0.48). Our findings support a link between RT skills and muscular fitness. Other associations were statistically significant but small in magnitude, and should therefore be interpreted cautiously.  相似文献   

Influence of different attentional focus on EMG amplitude and contraction duration during the bench press at different speeds     

Joaquin Calatayud  Jonas Vinstrup  Markus D. Jakobsen  Emil Sundstrup  Juan Carlos Colado  Lars L. Andersen 《Journal of sports sciences》2018,36(10):1162-1166

The purpose of this study was to investigate whether using different focus affects electromyographic (EMG) amplitude and contraction duration during bench press performed at explosive and controlled speeds. Eighteen young male individuals were familiarized with the procedure and performed the one-maximum repetition (1RM) test in the first session. In the second session, participants performed the bench press exercise at 50% of the 1RM with 3 different attentional focuses (regular focus on moving the load vs contracting the pectoralis vs contracting the triceps) at 2 speed conditions (controlled vs maximal speed). During the controlled speed condition, focusing on using either the pectoralis or the triceps muscles increased pectoralis normalized EMG (nEMG) by 6% (95% CI 3–8%; p = 0.0001) and 4% nEMG (95% CI 1–7%; p = 0.0096), respectively, compared with the regular focus condition. Triceps activity was increased by 4% nEMG (95% CI 0–7%; p = 0.0308) at the controlled speed condition during the triceps focus. During the explosive speed condition, the use of different focuses had no effect. The different attentional focus resulted in comparable contraction duration for the measured muscles when the exercise was performed explosively. Using internal focus to increase EMG amplitude seems to function only during conditions of controlled speed.  相似文献   

Does inside passing contribute to the high incidence of groin injuries in soccer? A biomechanical analysis     

Thomas Dupré  Johannes Funken  Ralf Müller  Kristian R. L. Mortensen  Filip Gertz Lysdal  Markus Braun 《Journal of sports sciences》2018,36(16):1827-1835

Groin injuries are common in soccer and often cause time-loss from training. While groin injuries have been linked to full effort kicking, the role of inside passing is unclear. Therefore, the purpose of this study was to investigate hip joint kinematics and muscle force, stress and contraction velocity for adductor longus and gracilis during inside passing. 3D kinematics of ten soccer players (23.4 yrs; 77.5 kg; 1.81 m) were captured with a motion capture system inside a Footbonaut. Muscle force and contraction velocity were determined with AnyBody Modelling System. Gracilis muscle forces were 9% lower compared to adductor longus (p = 0.005), but muscle stress was 183% higher in gracilis (p = 0.005). Contraction velocity reveals eccentric contraction of gracilis in the last quarter of the swing phase. Considering the combination of eccentric contraction, high muscle stress and the repetitive nature of inside passing, gracilis accumulates high loads in matches and training. These results indicate that the high incidence of groin injuries in soccer could be linked to isolated pass training. Practitioners need to be aware of the risk and refrain from sudden increases in the amount of pass training. This gives the musculoskeletal system time to adapt and might avoid career threatening injuries.  相似文献   

赵堡太极拳“五需”妙义析     

李全海  王英杰  刘文碧 《中华武术(研究)》2021,(3):89-91

本研究以《太极拳正宗论五字妙诀》为蓝本,从笔者赵堡太极拳修炼实际出发,研究认为,"心静、身灵、气敛、劲整、神聚"的诀要首在其十个字的"五需"要求,这是太极拳的修炼基准与境界达成的前提和妙引。因此,基于"妙诀全文",给出了"五需"的"义解",以便助益于修炼体认与理解。  相似文献   

肢体间不对称对运动表现的影响及干预手段     

李丹阳  程序  阙怡琳  倪丽丽 《武汉体育学院学报》2021,55(8):94-100

肢体间不对称是当前国际体能训练研究领域的热点问题。梳理国际权威研究成果,厘清肢体间不对称的概念和内涵,探究肢体间不对称与运动表现的关系、肢体不对称的评估方式、肢体间不对称的干预方法。主要结论：第一,肢体间不对称主要是指身体左右两侧肢体结构、动作模式、运动能力和运动技能的差异;第二,肢体间不对称直接影响爆发力输出、多向速度、离心-向心能力、平衡能力,潜在影响运动经济性、动作模式及专项运动技能的发挥;第三,肢体间不对称的干预方式为力量和爆发力训练（双侧和单侧）、快速伸缩复合训练、核心区训练、平衡能力训练等。建议在训练实践中应将肢体不对称与基础力量、爆发力等测评结合起来,以优化精英运动员的评估体系;应对运动员的肢体间不对称进行持续的动态监控,探索肢体间不对称与多种运动能力、神经肌肉疲劳等多种能力的交互影响,为调控训练计划提供指南。  相似文献   

赛事认同对标志性体育赛事发展影响的实证研究——基于多中介的调节模型     

王飞  张瑞林 《武汉体育学院学报》2021,55(12):56-64

赛事认同关乎标志性体育赛事的长期稳定发展。基于认同理论,运用Bootstrap、线性回归方法展开赛事认同对标志性体育赛事发展影响机理的实证研究。结果显示:赛事认同对标志性体育赛事中赛事质量、赛事环境、赛事营销和赛事管理服务均具有显著的影响;赛事品牌形象在赛事认同与赛事环境和赛事管理服务的影响关系间具有部分中介作用;举办地意向在赛事认同与赛事质量、赛事环境和赛事营销的影响关系间具有部分中介作用;参与意愿在赛事认同与赛事质量、赛事环境、赛事营销和赛事管理服务的影响关系间具有部分中介作用;感知价值在赛事认同与赛事管理服务的影响关系间具有部分中介作用;感知综合实力分别对赛事认同与赛事质量、赛事环境、赛事营销、赛事管理服务的影响关系起调节作用。研究证明了赛事认同与标志性体育赛事发展的关系路径,为促进我国标志性体育赛事高质量发展提供理论参考与实践支撑。  相似文献   

离心运动伴不同程度的血流限制对外周疲劳及心脏自主神经功能的效应研究     

潘颖  赵彦  田宜鑫  马晓缓  谭朝文  俞莹莹 《中国体育科技》2021,(2):28-36

目的:探讨急性离心运动伴4种不同程度的血流限制对年轻女性外周疲劳及心脏自主神经功能的影响,综合评价各方案的安全性,为长期血流限制运动干预提供参考。方法:将40名女大学生随机分为4组,分别进行小强度抗阻(30%1RM)伴0%(CON组)、40%(BFR₄₀组)、60%(BFR₆₀组)和80%(BFR80组)动脉闭塞压(AOP)的血流限制运动。各小组进行4组伸膝离心运动,第1组重复30次,后3组重复15次,组间休息30 s。检测运动前、运动后即刻、15 min、30 min、1 h以及24 h的骨骼肌收缩性能(最大径向位移、收缩速度)、最大等长力量和心脏自主神经功能。结果:1)与CON组相比,BFR₄₀组的副交感神经活性受到轻微抑制(P<0.05),可在运动后30 min内恢复(P>0.05);2)BFR₆₀组的最大等长力量在运动后显著下降(P<0.01),副交感神经活性进一步抑制(P<0.01),交感神经支配增强(P<0.05),运动后30 min内恢复交感—副交感神经的平衡性(P>0.05);3)BFR80组运动后诱发显著的外周疲劳(P<0.01),使副交感恢复显著延迟,交感活性大幅增强(P<0.05),需更长时间恢复交感—副交感神经的平衡性(24 h内);4)相关性分析显示,副交感神经活性分别与最大径向位移(r=0.65)、收缩速度(r=0.62)和最大等长力量(r=0.55)呈正相关(P<0.05),交感神经活性与上述3个指标呈负相关(P<0.05)。结论:血流限制运动中,40%AOP会抑制迷走神经活性;60%AOP可明显影响交感神经活性和交感—副交感调控的平衡性;80%AOP可诱发显著的外周疲劳,且与心脏自主神经调控密切相关。综上所述,不建议心血管风险高的患者使用80%AOP训练。  相似文献   

利用氟石膏代替天然石膏作水泥缓凝剂的试验   总被引：2，自引：0，他引：2  

朱晓莉  杨晓雯 《唐山学院学报》1999,(4)

用氟石膏作缓凝剂,具有与天然石膏相同的缓凝作用,同时对矿渣还有一定的激发作用,可增加水泥强度．此外,还可降低水泥成本,获得可观的经济效益．  相似文献