A motion-assisted positioning arm for a medical procedure. The positioning arm includes a base, an arm coupled to the base, and an end effector coupled to the arm. The arm includes a plurality of arm segments. The arm includes a plurality of joints for connecting the arm segments. The end effector may be manipulable with six degrees of freedom in a task-coordinate space based on motion by at least one joint in the plurality of joints. The positioning arm includes a processor to: detect manipulation of and determine forces or torques acting on the end effector; determine a surgical mode for constraining movement of the end effector in the task-coordinate space; determine an end effector velocity based on the determined forces or torques and the surgical mode for moving end effector; and apply at least one joint space movement based on the end effector velocity.