Kinematics and kinetics of youth baseball pitching with standard and lightweight balls

Because youth athletes are smaller and weaker than their adult counterparts, smaller equipment and fields are often used in youth sports. Previous research has shown that youth baseball pitchers use similar motions to older pitchers, but generate lower kinetics and angular velocities at the shoulder and elbow. The purpose of this study was to determine potential biomechanical benefits for youth pitchers to use lighter baseballs. Thirty-four youth (11.1 ± 0.7 years) pitchers pitched both standard [5 ounce (142 g)] and lightweight [4 ounce(113 g)] baseballs in a laboratory setting. Kinematic and kinetic parameters were measured with a six-camera high-speed motion analysis system. Three repeated measures MANOVAs were used to compare (p > 0.05) position, velocity, and kinetic parameters between the standard and lightweight baseballs. Subjective data were also collected. Pitching the lightweight ball produced no difference in arm position, but greater shoulder, elbow, and ball velocities. With the lightweight ball, pitchers produced decreased kinetics.Post-hoc analysis of the kinetic data revealed significant decreases in elbow varus torque and shoulder internal rotation torque. The data suggest that playing with lightweight baseballs may reduce the risk of overuse injury in the youth pitcher and also help develop arm speed. However, before introducing lightweight baseballs into the youth game, the effect of lighter, faster pitched balls for the batters and fielders should also be considered.     

Reply to Glazier: “Comment on ‘Influence of shaft length on golf driving performance’”

Abstract

In this study we compared the kinematic features of the throwing motion between young baseball players of different age groups. Forty‐four Japanese baseball players aged 6.1 to 12.3 years who regularly played baseball, including pitchers and position players, had their throwing actions analyzed three‐dimensionally using high speed videography. Of this sample, 26 players aged above 9 years of age were categorized as the senior group, while the remaining 18 were categorized as the junior group. Senior group throwers had greater height and body mass, and produced a greater ball speed than junior group throwers. The throwing arm movement of senior group throwers was similar to that of adult skilled players. However, in the junior group throwers, the shoulder horizontal adduction angle was larger during the arm acceleration phase, and the maximum angular velocities of elbow extension and shoulder internal rotation occurred later than in senior group throwers. These results indicate that players aged above 9 years can acquire a mature throwing arm movement, while players younger than that will use an immature motion. A possible reason why these differences were shown is that the official baseball is relatively heavy for junior group throwers; they would be better advised to use a lighter ball in throwing practice.     

对我国优秀标枪运动员最后用力时相投掷臂肘关节角度以及手腕控枪动作特点的重新审视

针对目前学术界出现的"伸直"派和"未完全伸直"派两大观点,作者对我国优秀男女标枪运动员在最后用力时相标枪出手瞬间肘关节所呈现的角度变化以及手腕控枪动作特点进行深入的剖析。得出:(1)在标枪出手瞬间,手腕握枪的形态是掌心向上、引枪臂呈微曲(未完全伸直)状况;(2)从运动力学的角度讲,直臂引枪能增加最后用力时的工作距离,具有一定的合理性,但是从手臂做鞭打动作时的生物学和技术形态学角度来看,它既不符合肌肉用力的生物学特点,也不符合技术形态学特点。     

肘关节夹的研制及其在排球垫球教学中的作用

排球垫球技术是高校体育教学的重要内容,在此技术的教学中,教师常感到在大纲规定的教学时数内,学生难以正确掌握动作技术。根据条件限制有助于正确动作形成这一原理,研制了“肘关节夹”。通过教学实践证明：肘关节夹有助于排球垫球技术的正确掌握（Ｐ﹤０．０１）,具有切实可行的推广价值。     

手法整复治疗儿童伸直型严重移位肱骨髁上骨折

通过67例儿童严重移位的肱骨髁上骨折的手法整复治疗，认为骨折的尽早良好复位、合理的外固定和尽可能的缩短固定时间，肘部软组织损伤的及时有效处理，医生指导下的功能锻炼贯穿于治疗的全过程，解除固定后功能康复的综合治疗，可减少肱骨髁上骨折所引起的肘     

简易力量测试法和等速肌力测试相关性研究

目的:探讨体质监测中握力、下肢蹬踏爆发力作为力量素质的简易测试法能否反映人体的力量素质。方法:随机抽取311例上海市普通市民,进行握力,下肢蹬踏爆发力,肘、膝关节运动速度为60°/s的等速向心力量测试。对握力与肘关节等速向心力量,下肢蹬踏爆发力与膝关节等速向心力量进行相关性统计分析。结果:握力与肘关节屈肌峰力矩正相关(r=0.815),与肘关节屈肌相对峰力矩正相关(r=0.712);下肢蹬踏爆发力与膝关节屈肌峰力矩正相关(r=0.764),与伸肌峰力矩正相关(r=0.766);结论:握力、下肢蹬踏爆发力可以作为人体力量素质的简易测试方法并可应用于体质监测工作中。     

超等长式俯卧撑练习对推铅球技术和成绩的影响

为解决普体铅球课进行身体训练受学校场地、器材设备限制的困难，选用超等长式俯卧撑练习作为训练手段，通过实验与对照的方法，发现超等长式俯卧撑练习可有效地挖掘学生自身爆发力的潜在素质，迅速提高铅球成绩，并对推铅球最后用力出手时易产生的“掉肘”错误动作有明显的纠正作用。     

对皖西民俗体育“肘阁、抬阁”的现代生成机制研究

以皖西民俗体育肘阁、抬阁为个案,研究民俗体育融入现代生活存在的制约因素及路径选择,同时,从非物质文化遗产保护的角度探讨民俗体育的可持续发展。探讨非物质文化遗产保护下皖西民俗体育“肘阁、抬阁”的传承和发展。结果显示：社会的快速转型给民俗体育的传承和保护带来了严峻的挑战,在对民俗体育传承和保护的过程中体现出多元素融合的特点。充分挖掘民俗体育的文化内涵,探讨其融入现代生活的生成机制,才是民俗体育得以传承的最佳方式。     

对Elliott“生物力学与网球”一文的述评

在网球比赛中取胜,需要有天赋的运动员、优秀的教练员、适合的器材,以及对这个运动项目相关的体育科学的有关方面的理解。本文从体育科学和运动医学角度阐述了生物力学在运动员发展中的作用。生物力学在运动员发展中起着关键性的作用,因为所有的击球都具有一个基本的力学结构,运动损伤都是由于力学因素引起的。这篇发表在《英国运动医学杂志》上的研究综述从不同角度论述了网球运动中的生物力学问题。文章全面涵盖了网球运动所涉及的生物力学一般理论、网球运动技术和网球运动损伤生物力学。文章作者Bruce Elliott教授长期从事网球等运动的生物力学研究,是国际著名的运动生物力学专家,曾为国际运动生物力学学会（International Society of Biomechanics in Sports,ISBS）主席。     

优秀乒乓球运动员肘关节等动屈伸运动时拮抗肌共激活现象研究

目的:研究优秀乒乓球运动员和普通在校大学生肘关节拮抗肌活动在等动屈伸过程中的差异。方法:以8名优秀乒乓球运动员和8名普通高校大学生为研究对象,利用Biodex等动测试仪和Noraxon表面肌电仪记录上肢肘关节等动屈伸过程中作为拮抗肌的肱二头肌和肱三头肌的力量特征和表面肌电信号特征。肘关节伸肌和屈肌分别在最大等长收缩、15°/s、30°/s、60°/s、120°/s、180°/s、240°/s条件下进行3次最大等动离心屈伸运动。以标准化的均方根振幅(RMS)和标准化的峰值力矩作为评价指标。结果:对于大学生和优秀乒乓球运动员来说,随着肘关节速度的增加,两组受试者的屈伸肌力矩都呈下降趋势,大学生表现为速度大于60°/s时伸肌力矩大于屈肌力矩(P<0.05),优秀乒乓球运动员表现为伸肌力矩低于屈肌力矩,但没有统计学差别(P>0.05)。大学生和优秀乒乓球运动员都表现为在向心收缩时不同速度下随着主动肌力矩下降,拮抗肌激活水平表现为逐渐增高,且所有线性拟合系数r2>0.7。优秀乒乓球运动员拮抗肌肱三头肌的激活水平(在MVC时:10.1%±5.2%,240°/s时:15.1%±6.6%)要显著低于普通高校大学生(MVC时:29.3%±8.8%,240°/s时:38.0%±15.1%)。而作为拮抗肌的肱二头肌激活水平在普通大学生和优秀乒乓球运动员之间没有统计学差异(P>0.05)。优秀乒乓球运动员拮抗肌/主动肌肌电活动比要显著低于普通大学生(P<0.05)。结论:与普通大学生相比,优秀乒乓球运动员肘关节拮抗肌肱三头肌的激活水平要更低,这可能是优秀乒乓球运动员对肘关节周围肌肉进行长期训练的结果。而两者拮抗肌肱二头肌激活水平没有统计学差异,其原因可能是由于两者在日常活动中肱二头肌作为拮抗肌经常为了克服地心引力受到同样的刺激造成的。