Movement and force dynamics in bimanual cooperative tasks in chronic stroke and healthy individuals

Stroke rehabilitation often involves the use of haptic robots to improve motor control and bimanual coordination. This study examines how damping affects movement and force dynamics in bimanual tasks performed by healthy participants and participants with chronic stroke using a haptic robotic system equipped with force sensors for each hand. Participants completed tasks at three damping levels: $0\frac{N}{m/s}$ (no damping), $20\frac{N}{m/s}$ (low damping), and $40\frac{N}{m/s}$ (moderate damping). Key parameters for trajectory of movement, velocity, manipulation force, and internal force were analyzed to assess movement stability and control. The results revealed that damping $20\frac{N}{m/s}$ effectively stabilized movements in persons with stroke, reducing velocity deviations and making their performance more comparable to healthy participants, without introducing excessive resistance. In contrast, damping $40\frac{N}{m/s}$ acted as resistance training. Participants with stroke exhibited consistently higher internal forces than healthy participants, reflecting compensatory strategies and inefficient motor control. These findings demonstrate that low damping ($20\frac{N}{m/s}$) offers an optimal balance between movement stabilization and resistance, highlighting its potential as a rehabilitation strategy, while moderate damping ($40\frac{N}{m/s}$) may be reserved for resistance training.