Identification of human feedforward control in grasp and twist tasks

Grasping and twisting are basic motor skills for the execution of activities in daily life such as opening a door with a door knob. We study the relationship between grip force and hand trajectory during a grasp and twist task when unexpected load torques are encountered. The experimental results on grip force development and hand trajectories are consistent with similar studies on grasp and lift tasks in the literature. We also seek to build a simple model to study human feedforward control during grasp and twist movement. Our model includes a position source and driving point impedance. We provide detailed procedures to identify the relationship between the impedance values and grip forces and the algorithm to estimate the position source. We check our model by comparing the model prediction and experimental data on certain catch trial trajectories.