Reaching movements performed from a crouched body posture require a shift of body weight from both arms to one arm. This situation has remained unexamined despite the analogous load requirements during step initiation and the many studies of reaching from a seated or standing posture. To determine whether the body weight shift involves anticipatory or exclusively reactive control we obtained force plate records, hand kinematics, and arm muscle activity from 11 healthy right-handed participants. They performed reaching movements with their left and right arm in two speed contexts - 'comfortable' and 'as fast as possible' - and two postural contexts - a less stable knees-together posture and more stable knees-apart posture. Weight-shifts involved anticipatory postural actions (APA) by the reaching and stance arms that were opposing in the vertical axis and aligned in the side-to-side axis similar to APAs by the legs for step initiation. Weight-shift APAs were correlated in time and magnitude, present in both speed contexts, more vigorous with the knees placed together, and similar when reaching with the dominant or non-dominant arm. The initial weight-shift was preceded by bursts of muscle activity in the shoulder and elbow extensors (posterior deltoid and triceps lateral) of the reach arm and shoulder flexor (pectoralis major) of the stance arm which indicates their causal role; leg muscles may have indirectly contributed but were not recorded. The strong functional similarity of weight-shift APAs during crouched reaching to human stepping and cats reaching suggests that they are a core feature of posture-movement coordination.

中文翻译：

---

从蹲伏姿势伸手时手臂之间的预期重量转移

从蹲下的身体姿势进行伸展运动需要将体重从双臂转移到单臂。尽管在踏步开始时有类似的负荷要求以及从坐姿或站立姿势伸手的许多研究，但这种情况仍未得到检验。为了确定体重转移是否涉及预期控制或完全反应控制，我们从 11 名健康的右手参与者那里获得了测力板记录、手部运动学和手臂肌肉活动。他们用左右臂在两种速度环境（“舒适”和“尽可能快”）和两种姿势环境（一种不太稳定的膝盖并拢姿势和更稳定的膝盖分开姿势）下进行了伸展运动。重量转移涉及通过伸展臂和站立臂的预期姿势动作 (APA)，这些臂在垂直轴上相对，并在左右轴上对齐，类似于腿部的 APA，用于踏步。重量转移 APA 在时间和幅度上具有相关性，在两种速度环境中都存在，膝盖并拢时更有力，而在使用优势或非优势臂时相似。在最初的体重转移之前，伸展臂的肩部和肘部伸肌（三角肌后束和肱三头肌外侧）和站立臂的肩屈肌（胸大肌）的肌肉活动爆发，这表明了它们的因果关系；腿部肌肉可能有间接贡献，但没有记录。