Lee W A, Michaels C F, Pai Y C
Programs in Physical Therapy, Northwestern University, Chicago, IL 60611.
Exp Brain Res. 1990;82(2):304-14. doi: 10.1007/BF00231250.
This study examined whether the torques and EMG activity that precede and accompany bilateral arm pulls made by standing humans demonstrate a pulse height form of organization. Nine adults made abrupt bilateral pulls in the sagittal plane against a handle, to force targets equal to 5, 10, 20, 40, 60, 80 and 95% of their maximal pulling force (%MPF). The force applied at the handle, ground reaction forces, the center of pressure (CP), and EMG activity in gastrocnemius (GS), biceps femoris (BF), tibialis anterior (TA) and quadriceps (QD) muscles were recorded. Our analysis divided the action into a pre-pull phase (events prior to the increase of handle force) and a pulling phase (while handle force was greater than zero). We evaluated the effects of %MPF on the durations and peak amplitudes of the pre-pull and pulling angular impulses about the ankle joint and on pre-pull EMG patterns. The results showed that the angular impulse associated with the pulling torque (due to the reactive force on the body during the pull) had a pulse height organization: peak torque increased linearly with %MPF, and the durations of the pulling torque were relatively constant. In contrast, a pulse height organization did not characterize the pre-pull period for either the angular impulse associated with ankle torque (due to net ground reaction force) or EMG activity in the leg muscles. Rather, peak ankle torque typically increased up to some submaximal %MPF and then plateaued, perhaps due to a constraining effect on foot length on CP. The durations of pre-pull ankle torques increased over the whole range of %MPF, thereby compensating for the limit on ankle torque. Depending on the subject, the muscles were recruited in two different orders: GS-BF-TA-QD, or GS-TA-BF-QD. As the %MPF increased, the EMG onset times of all four muscles occurred earlier, and there was a greater likelihood that the BF, TA and QD muscles would be recruited on a given trial. The changes in the ankle torque and EMG patterns were gradual, suggesting that the pre-pull phase could have one underlying form of organization, with parameters that are tuned to task goals and anatomical constraints.
本研究考察了站立的人进行双侧手臂拉伸之前及过程中的扭矩和肌电图（EMG）活动是否呈现脉冲高度形式的组织方式。九名成年人在矢状面内突然双侧拉动一个手柄，以达到相当于其最大拉力（%MPF）的5%、10%、20%、40%、60%、80%和95%的力目标。记录了手柄处施加的力、地面反作用力、压力中心（CP）以及腓肠肌（GS）、股二头肌（BF）、胫骨前肌（TA）和股四头肌（QD）的EMG活动。我们的分析将该动作分为预拉伸阶段（手柄力增加之前的事件）和拉伸阶段（手柄力大于零时）。我们评估了%MPF对踝关节预拉伸和拉伸角冲量的持续时间和峰值幅度以及预拉伸EMG模式的影响。结果表明，与拉伸扭矩相关的角冲量（由于拉伸过程中身体上的反作用力）具有脉冲高度组织方式：峰值扭矩随%MPF线性增加，且拉伸扭矩的持续时间相对恒定。相比之下，与踝关节扭矩相关的角冲量（由于地面净反作用力）或腿部肌肉的EMG活动在预拉伸阶段均未表现出脉冲高度组织方式。相反，峰值踝关节扭矩通常会增加到某个次最大%MPF，然后趋于平稳，这可能是由于CP处足长的限制作用。预拉伸踝关节扭矩的持续时间在整个%MPF范围内增加，从而补偿了踝关节扭矩的限制。根据受试者的不同，肌肉以两种不同的顺序被募集：GS - BF - TA - QD或GS - TA - BF - QD。随着%MPF的增加，所有四块肌肉的EMG起始时间都更早出现，并且在给定试验中BF、TA和QD肌肉被募集的可能性更大。踝关节扭矩和EMG模式的变化是渐进的，这表明预拉伸阶段可能具有一种潜在的组织形式，其参数根据任务目标和解剖学限制进行调整。
