Differences in pointing movement performance between healthy and post stroke adults

The exposure group will include 20 post stroke adults. This group will perform a pointing task using the more disable upper extremity from a sitting position and with the trunk vertical. The pointing task consists in indicating with the index finger five targets, projected on a panel in front of the participant and equally distributed in a semicircle. The center of the semicircle is aligned to the shoulder of the participant with a radius equal to 80% of arm length. Each of the targets will be pointed five times following the next consecutive steps: (1) hold the arm in a rest position (forearm resting on the leg) for 1 s. (2) move the arm at a preferred speed to point the lighted target with the index finger (3) hold steady pointing the target for 1s (4) move back the arm to the initial rest position The start of each step is indicated using sound (ie., beeps). In total, each participant will performed 25 trials (5 targets x 5 times). Before starting the pointing task, the weight of participants and length of their upper body segments (torso, arm, forearm, hand and clavicle) will be measured. Then, an electromyography surface sensor will be place in the supraspinatus, infraspinatus and teres minor muscles. Finally, 4 small plates containing 3 reflective markers each, will be placed on the participants’ joints (wrist, elbow, shoulder and clavicle). During the performance of the pointing task, the following measurements will be taken: (i) competition time, (ii) angular and Cartesian variables of joints, such as position, velocity and acceleration, (iii) dynamic variables, such as torques and derived metrics, such as mechanical work and movement smoothness, and (iv) EMG rectified signal of three muscles. All these measurements will be obtained from the integration and analysis in real time of raw data coming from a tracking camera (Optitrack V120) and a surface electromyography system (Delsys Bagnoli). Each participant of the Exposure Group will complete the pointing task on a session day, which will be organized chronologically as follows: (1) Take body weight and length segments measurements (2) Placement of 4 small plates of reflective markers on participant´s joints (3) Placement of 3 EMG surface sensors (4) Performance of the pointing task (n=6) (5) Removal of the reflective markers and EMG sensors A short practice period before starting step 4 will be considered and short breaks between the pointing of each target will be allowed. The total duration of the observation session will be approximately of 1 hour and 30 min.