On preparatory object rotation to adjust handle orientation for grasping

This study investigates preparatory rotation as a manipulation strategy for grasping objects from different presented orientations. Participants lifted heavy, handled objects from eight initial orientations under two task constraints. When object motion was permitted, participants used preparatory rotation to first adjust the object handle to a desired orientation before lifting. The amount of rotation increased for handle orientations further from the central orientation. When object motion was not permitted, increased upper body joint torque was required for the direct grasping strategy compared to that for the preparatory rotation strategy. Grasp configuration and ratings for comfort and naturalness also exhibited similar trends, leading to the conjecture that both energetic considerations and grasp kinematic considerations may drive the selection of preparatory rotation.