Jeon H S, Trimble M H, Brunt D, Robinson M E
Department of Physical Therapy, University of Florida, Gainesville 32610-0154, USA.
J Orthop Sports Phys Ther. 2001 Mar;31(3):122-9; discussion 130-2. doi: 10.2519/jospt.2001.31.3.122.
Single group repeated measures design.
To determine if the rate of transition between knee flexion and extension influences the subsequent concentric activation of the quadriceps and knee extension torque during reciprocal movements.
Preloading a muscle by stretching, a prior isometric or eccentric muscle action, or a prior movement controlled concentrically by the antagonist muscle group increases the maximal torque-generating capability of the agonist. We hypothesized that the rate of transition from the prior movement may be the critical factor that influences the degree of muscle facilitation and torque potentiation. Rapid reversal of antagonistic movements has been postulated as a potential facilitatory mechanism.
Knee extension torque and electromyographic (EMG) amplitude (dependent variables) from 2 of the vasti muscles were recorded while subjects (N = 20; 12 men, 8 women, mean age, 28.5+/-2.68 years) maximally activated their quadriceps at 3 constant angular velocities, 100 degrees/s, 200 degrees/s, and 300 degrees/s, and 2 preload conditions, SLOW and RAPID (independent variables). In the SLOW transition condition, subjects actively flexed their knee to 110 degrees from an extended position, paused in this position for 3 seconds, and then extended to 0 degrees. In the RAPID transition condition, the same movement from knee flexion to extension was performed without a pause.
Peak torque, the root-mean-square (RMS) average, peak (peak rectified and smoothed), and initial (100 milliseconds prior to torque onset) EMG amplitudes were all significantly greater during the RAPID transition condition. Peak torque decreased with increasing movement velocity. There were no interactions between the preload conditions and angular velocity on peak torque or the EMG amplitude variables. There was also no influence of velocity on the EMG amplitude variables.
The effect of preloading the quadriceps by prior concentric activation of the hamstrings is dependent on the rate of transition between the flexion and extension movements and is due primarily to neural facilitation.
单组重复测量设计。
确定膝关节屈伸转换速率是否会影响后续往复运动中股四头肌的向心激活和膝关节伸展扭矩。
通过拉伸、先前的等长或离心肌肉动作，或先前由拮抗肌群控制的向心运动对肌肉进行预加载，可增加主动肌产生最大扭矩的能力。我们假设先前运动的转换速率可能是影响肌肉易化程度和扭矩增强的关键因素。拮抗运动的快速逆转被认为是一种潜在的易化机制。
记录20名受试者（12名男性，8名女性，平均年龄28.5±2.68岁）在3种恒定角速度（100度/秒、200度/秒和300度/秒）以及2种预加载条件（慢和快，自变量）下最大程度激活股四头肌时的膝关节伸展扭矩和股外侧肌中2块肌肉的肌电图（EMG）幅度（因变量）。在慢转换条件下，受试者从伸展位主动屈膝至110度，在此位置停顿3秒，然后伸展至0度。在快转换条件下，进行相同的从屈膝到伸展的运动但不停顿。
在快转换条件下，峰值扭矩、均方根（RMS）平均值、峰值（整流和平滑后的峰值）以及初始（扭矩开始前100毫秒）EMG幅度均显著更大。峰值扭矩随运动速度增加而降低。预加载条件和角速度之间在峰值扭矩或EMG幅度变量上没有交互作用。速度对EMG幅度变量也没有影响。
通过先前绳肌的向心激活对股四头肌进行预加载的效果取决于屈伸运动之间的转换速率，且主要归因于神经易化。
