Enoka R M
Med Sci Sports. 1979 Summer;11(2):131-7.
Data from five experienced weightlifters on the vertical forces applied to the barbell and system (barbell and lifter) during the pull were in excellent agreement with earlier displacement-time descriptions of the double knee bend as consisting of two stages of extension interrupted by a period of realignment (second knee bend). The vertical component of the ground reaction force (Rz) consisted of three phases: Weighting I, Unweighting, and Weighting II. The relative magnitude of the Rz impulse with respect to the system weight impulse (as an indicant of the proportion of the Rz impulse contributing to system acceleration) ranged from 118--141% for Weighting I, 74--89% for Unweighting, and 122--135% for Weighting II. In agreement with published theoretical calculations the most experienced and successful lifter produced the larger phase of positive acceleration first. The rebending of the knees was associated with the Unweighting phase. Although this latter interval corresponded to a phase of barbell deceleration, it appeared that the concomitant enhancement of the back, hip, and knee extensor activity outweighed any adverse effects.
来自五名经验丰富的举重运动员在提拉过程中施加在杠铃和系统（杠铃和举重运动员）上的垂直力的数据，与早期对双膝弯曲的位移-时间描述非常一致，即双膝弯曲由两个伸展阶段组成，中间被一段重新调整（第二次膝盖弯曲）的时间打断。地面反作用力（Rz）的垂直分量包括三个阶段：加载I、卸载和加载II。Rz冲量相对于系统重量冲量的相对大小（作为Rz冲量对系统加速度贡献比例的指标），加载I阶段为118%-141%，卸载阶段为74%-89%，加载II阶段为122%-135%。与已发表的理论计算结果一致，最有经验且最成功的举重运动员首先产生了较大的正加速度阶段。膝盖的再次弯曲与卸载阶段相关。虽然这后一个时间段对应于杠铃减速阶段，但似乎背部、臀部和膝盖伸肌活动的同时增强超过了任何不利影响。
