Kelleran K J, Morrison S, Russell D M
Human Movement Sciences Department, Old Dominion University, Norfolk, VA, 23529, USA.
School of Physical Therapy and Athletic Training, Old Dominion University, Norfolk, VA, 23529, USA.
Exp Brain Res. 2016 Dec;234(12):3399-3409. doi: 10.1007/s00221-016-4738-x. Epub 2016 Jul 22.
The performance of fine motor tasks which require a degree of precision can be negatively affected by physiological tremor. This study examined the effect of different aiming positions on anterior-posterior (AP), medial-lateral (ML) and vertical (VT) postural tremor. Participants were required to aim a mock handgun at a target located in front of them at eye level. Changes in AP, ML and VT tremor from the forearm and gun barrel were assessed as a function of limb (i.e., whether one or both arms were used) and upper arm position (elbow bent or extended). Tremor was recorded using triaxial accelerometers. Results showed that, across all tasks, the ML and VT tremor for any point was characterized by two frequency peaks (between 1-4 and 8-12 Hz) with amplitude increasing from proximal (forearm) to distal (gun barrel). Interestingly, irrespective of the posture adopted, ML accelerations were of greater amplitude than VT oscillations. AP oscillations were markedly smaller compared to VT and ML tremor, did not display consistent frequency peaks, and were not altered by the arm conditions. Altering the aiming posture resulted in changes in VT and ML tremor amplitude, with oscillations being greater when using a single arm as compared to when two arms were used together. Similarly, tremor amplitude was reduced when the task was performed with the elbow bent compared to the straight arm condition. Overall, these results highlight that ML oscillations make as significant a contribution to the overall tremor dynamics as those observed in the VT direction. However, the origin of ML tremor is not simply the product of voluntary adjustments to maintain aim on the target, but also exhibits features similar to the neural generated 8-12-Hz tremor seen under postural conditions.
需要一定精确度的精细运动任务的表现可能会受到生理性震颤的负面影响。本研究考察了不同瞄准位置对前后（AP）、内外侧（ML）和垂直（VT）姿势性震颤的影响。参与者被要求用一把模拟手枪瞄准位于他们眼前视线高度的目标。评估了前臂和枪管在AP、ML和VT方向上震颤的变化，这些变化是肢体（即使用一只手臂还是两只手臂）和上臂位置（肘部弯曲或伸直）的函数。使用三轴加速度计记录震颤情况。结果表明，在所有任务中，任何点的ML和VT震颤都有两个频率峰值（1 - 4赫兹和8 - 12赫兹之间），且振幅从近端（前臂）到远端（枪管）逐渐增加。有趣的是，无论采用何种姿势，ML方向的加速度振幅都大于VT方向的振荡。与VT和ML震颤相比，AP方向的振荡明显较小，没有显示出一致的频率峰值，并且不受手臂条件的影响。改变瞄准姿势会导致VT和ML震颤振幅的变化，单臂使用时的振荡比双臂同时使用时更大。同样，与伸直手臂的情况相比，肘部弯曲执行任务时震颤振幅会降低。总体而言，这些结果突出表明，ML方向的振荡对整体震颤动态的贡献与VT方向观察到的贡献一样显著。然而，ML震颤的起源不仅仅是为了保持瞄准目标而进行的自愿调整的产物，还表现出与姿势条件下所见的神经源性8 - 12赫兹震颤相似的特征。
