Ando Luna, Itaguchi Yoshihiro
Department of Computer Science, Shizuoka University, Hamamatsu, 432-8011, Japan.
Department of Psychology, Keio University, 2-15-45 Mita, Minato-ku, Tokyo, 108-8345, Japan.
Exp Brain Res. 2022 May;240(5):1515-1528. doi: 10.1007/s00221-022-06350-6. Epub 2022 Mar 23.
Usually, our bodily movements are performed against gravity. Most studies using a force field have focused on adaptation processes to force applied in the horizontal plane, which is novel to us, but not to force in the gravitational direction. The present study investigated the immediate effects (aftereffects) of a force toward the gravitational direction on the kinematics of reach-to-grasp movements as well as short-term adaptation to the force, simply by adding a weight to participants' forearm. Healthy young adults performed blocks of 10 reach-to-grasp movements under three weight conditions; as the weights were changed between blocks, the participants experienced weight changes ranging from - 200 to + 200 g. We obtained three main results; first, the height of movement trajectory (trajectory height) was remarkably higher immediately after the forearm weight changed to lighter than after the weight changed to heavier, suggesting that participants planed the trajectory height with the same muscle efforts as in the previous trial. Second, the trajectory height at the end of the block became higher only in 200 g condition, indicating that the participants could not achieve same trajectory height as that without any weight load, at least in ten trials of adaptation period to the 200 g weight load. Third, the coordination between reach and grasp components was preserved immediately after forearm-weight changes. These findings may contribute to further understand how we perform adaptive reach-to-grasp movements with frequent weight changes that are inevitable in everyday life.
通常，我们的身体运动是在对抗重力的情况下进行的。大多数使用力场的研究都集中在对水平面施加的力的适应过程上，这对我们来说是新奇的，但对于重力方向的力并非如此。本研究仅通过在参与者的前臂上增加重量，来探究重力方向的力对伸手抓握动作运动学的即时影响（后效应）以及对该力的短期适应情况。健康的年轻成年人在三种重量条件下进行了每组10次的伸手抓握动作；由于组间重量发生变化，参与者经历了从 -200 克到 +200 克的重量变化。我们得到了三个主要结果：第一，前臂重量变轻后，运动轨迹的高度（轨迹高度）明显高于重量变重后，这表明参与者以与之前试验相同的肌肉力量来规划轨迹高度。第二，仅在200克的条件下，组末的轨迹高度才会变高，这表明至少在对200克重量负荷的十次适应试验中，参与者无法达到无重量负荷时的相同轨迹高度。第三，前臂重量变化后，伸手和抓握动作成分之间的协调性立即得到保持。这些发现可能有助于进一步理解我们如何在日常生活中不可避免的频繁重量变化情况下进行适应性伸手抓握动作。
