(1) Background: Mirror therapy is one of the promising interventions for the upper limb rehabilitation of stroke patients. Postural asymmetry during mirror therapy was pointed out as a possibility to influence stroke patients' rehabilitation negatively. However, it is still difficult to find studies on the postural changes in mirror therapy concept interventions. This study compared three methods of postural differences as follows: traditional mirror therapy (mirror); displaying the real-time movement of the unaffected side on the screen above the affected side (screen); and playing a pre-recorded movement of the unaffected side on a tablet placed on a movable box where the affected hand is put inside (movable). (2) Methods: to observe a kinematic difference, we recruited 16 healthy volunteers to go through three different interventions (mirror, screen, movable). The motion capture system made observations on the postures before and during interventions, then compared and analyzed. (3) Results: while using the mirror, the sitting posture was observed to become asymmetric, and the following unique posture was observed where the target hand went further from the trunk while performing tasks. In addition, the shoulder of the target side came forward, and the difference between both elbow flexion angles was also observed. On the other hand, the screen or movable device did not cause a significant change in the sitting posture, and no additional postural differences were observed either. (4) Conclusions: mirror therapy showed a tendency to cause lateral flexion opposite the target hand, thus, creating additional postural change. However, developed methods controlled spine tilt, and enabled the keeping of the midline while sitting during the intervention.
Keywords: kinematic analysis; mirror therapy; posture; virtual reality.