Shintaro Uehara

INTRODUCTION: Sitting activities involve trunk leaning, which requires precise coordination of the head, trunk, and pelvis to maintain the center of pressure (COP) within limits of stability. However, how the movement in each segment is associated with COP displacement remains unclear. METHODS: Twenty-eight healthy volunteers performed seated trunk leaning twice in left, right, forward, and backward directions. COP displacements and angular changes were measured in head, trunk, and pelvic tilt in all directions, and additionally in the hip during forward-backward leaning. Within-session reliability of measured indices was assessed using intraclass correlation coefficients (ICCs) and Bland-Altman analyses, and relationships between segment angle changes and COP displacements were examined using mixed-effects models. RESULTS: ICCs between two trials showed substantial to very high correlations (ICC = 0.84-0.95), and Bland-Altman analyses showed neither fixed nor proportional bias, suggesting sufficient reliability. Pelvic tilt angle changes were significantly associated with COP displacements during left-right and forward-backward leaning (p < 0.001). Head, trunk, and hip angle changes were also significantly associated with COP displacement during forward-backward leaning (all p < 0.01). CONCLUSIONS: Pelvic tilt was associated with COP displacement during leaning, regardless of direction, indicating the importance of pelvic shifts in strategies for maintaining sitting balance in healthy adults.

OBJECTIVES: To investigate the feasibility of robot-assisted hand movement training using a novel end-effector robot in individuals after stroke. METHODS: Eleven individuals with subacute stroke with hand motor impairment underwent robot-assisted repetitive finger flexion/extension for 20 min daily and repeated this training on 7 non-consecutive days. The robot was designed to allow the flexion and extension of the metacarpophalangeal and proximal interphalangeal joints of the index to the little fingers, and to provide assistive torque if the movement did not reach the target angle within a limited time. We assessed the co-contraction index (CCI) of the flexor digitorum superficialis and extensor digitorum muscles and assessed the active range of motion (AROM) of the index finger before and after training each day (intra-day effect). We performed clinical assessments of motor function and spasticity and evaluated the CCI and AROM before and immediately after the 7-day training (inter-day effect). RESULTS: Ten participants completed the 7-day training. For the intra-day effect, the CCI was significantly decreased immediately after training, particularly during active finger flexion, and the AROM tended to improve from the middle of the training days. For the inter-day effect, there were no significant changes in the Stroke Impairment Assessment Set for Finger Function, modified Ashworth scale, CCI, or AROM after the 7-day training. CONCLUSIONS: Repetitive finger movement training with the assistance of the novel robot improves muscle activation patterns, reducing co-activation between the agonist and antagonist muscles immediately after training.