Impact of hemispheric specialization on reactive upper limb motor control after perturbations via a newly designed reactive pinch-holding-up activity test

Background: Reactive motor control is essential for optimizing movements, particularly in response to unexpected perturbations. Although hemispheric specialization is known to influence motor performance, its role in reactive motor control during fine motor tasks remains uncertain. This study aimed to develop a reliable reactive Pinch-Holding-Up Activity test to deliver controlled perturbations and measure reactive responses, evaluate the effects of various perturbation scenarios on grip responses, and investigate hemispheric influences on motor adaptation. Methods: This cross-sectional observational study recruited 20 right-handed young adults to assess the reliability of the test and 26 participants to investigate the effects of hemispheric specialization. The reactive Pinch-Holding-Up Activity test comprised three conditions: predictive perturbation, unpredictable perturbation during holding, and unpredictable perturbation during lifting. Key parameters analyzed included reaction time, time to regain grip stability, peak grip force, force ratio, and baseline pinch force. Findings: The test demonstrated good reliability, with the intraclass correlation coefficient improving from 0.571 to 0.868 after removing outliers. In the perturbation during lifting condition, both hands exhibited lower peak grip force compared to the perturbation during holding condition (p = 0.002 for the right hand; p < 0.001 for the left hand). The left hand showed greater precision in timing and force adjustments under both holding and lifting conditions (p < 0.05). Interpretation: These findings indicate that the test is a reliable tool for assessing fine motor control and reveal hemispheric differences in reactive motor adaptation. The left hand's superior precision under unpredictable conditions suggests potential applications in rehabilitation and motor adaptation research.