Kinematic data acquisition and processing
head and trunk positions, clavicular notch, tremor, inferior lip, wrist joints
Data acquisition was carried out by means of an optical motion capture system equipped with 8 infrared cameras set at a sampling rate of 120 Hz (SMART-D, BTS Bioengineering, Milan, Italy). Retro-reflective markers (14 mm diameter) were positioned bilaterally on the acromion, lateral humeral epicondyle, ulnar and radial styloid processes, on second metacarpal head and on the fingertip to identify the position and orientation of, respectively, the upper arm, forearm, and hand. The head and trunk positions were estimated through markers positioned respectively on the zygomatic, nasion processes and mouth under the inferior lip (head), right and left acromion, clavicular notch and spinous processes of C7 and T8 vertebrae (trunk) according to standardized protocols previously employed for similar purposes [ Going phase, which identifies the hand movement from the table to the mouth Adjusting phase, dedicated to precisely locating the mouth Returning phase, during which the hand is moved back to the initial positionIn particular, the beginning of the going phase was identified as the point in time at which the linear velocity of the fingertip marker exceeded 20% of the peak velocity [Each participant’s performance was further quantitatively characterized by calculating: Total movement duration (s). Time needed to complete going, adjusting, and return phases (s). Index of curvature: which is a dimensionless parameter obtained by dividing the length of the 3D trajectory of the marker placed on the fingertip and the linear distance between its initial position and the target (i.e., mouth [ Number of movement units: that is, the number of velocity peaks that exceeded the 10% of the maximum velocity calculated across the entire task. Such value is representative of repeated accelerations and decelerations during movement performance and reflects efficiency and smoothness of movement [ Frequency of changes in direction (Hz): this is another measure of smoothness which characterizes the finger displacements associated to the possible presence of tremor [While the listed parameters are the most commonly employed to characterize the HTM performance from a kinematic point of view, it is noteworthy that the employed marker set also allows to obtain data about the angular trends at shoulder, elbow, and wrist joints during the movement execution. However, for the sake of brevity, such data will not be presented here.