Direction and distance dependency of reaching movements of lower limb

Efficient movement of the body is an important part of our daily lives, which we perform unconsciously. Such efficient movements have been investigated using reaching movements in the upper limb, and whose kinematics reportedly vary depending on the movement direction. However, the reaching movements of the lower limbs are not well understood. Therefore, we aimed to examine changes in the kinematics of the lower limb reaching movements to determine the mechanism of skilled motor ability in terms of direction and distance. Sixteen adults (10 males) were requested to reach targets projected on the floor in seven directions and at three distances, for a total of 21 points. We found that the reaching time slowed down for the contralateral side (right foot to left-sided target), and was caused by a slower start of the toe movement. To identify the cause of this delay, we analyzed the onset of movement at each joint and found that movement to the contralateral side began closer to the torso than movement to the ipsilateral side. The time-to-peak velocity was also calculated; the motion required to reach the target in the shortest time varied depending on the direction and distance. Acceleration phases that were not observed in the upper limb velocity profile were observed in the lower limb velocity profiles. These results suggest that movement kinematics vary with direction and distance, resulting in slower reaching time on the contralateral side.