Interlimb differences in reach-to-grasp coordination under goal- and dynamics-related perturbations.

Interlimb asymmetries in motor control are well documented in simplified tasks, but their expression in coordinated reach-to-grasp actions under perturbation remains unclear. Here, we examined whether differences between the dominant (DH) and non-dominant hand (NDH) emerge during online adjustments of reach-to-grasp movements. Participants (n = 12; 5 female, 7 male) performed reach-to-grasp actions in a virtual environment under control, visual perturbation, and mechanical perturbation conditions. Kinematic and electromyographic (EMG) measures were analyzed, and baseline-corrected values were used to isolate perturbation-specific effects. Under control conditions, differences between hands were minimal and limited to peak transport velocity and proximal muscle activity. During perturbations, analyses performed prior to baseline correction revealed a significant Hand × Perturbation interaction for index-finger curvature, indicating hand-dependent distal reorganization during mechanical perturbation. Crucially, applying baseline correction to isolate perturbation-driven effects eliminated most global kinematic asymmetries, while revealing greater transport deceleration and triceps brachii activity in the NDH and greater index-finger curvature and extensor indicis activity in the DH during mechanical perturbation. In contrast, visual perturbations elicited largely symmetric responses across both limbs. These results indicate that interlimb differences in reach-to-grasp are not expressed as stable, fixed traits, but emerge selectively under mechanical perturbation. The observed pattern suggests that lateralized coordination strategies depend on the specific demands of the task, with the DH showing greater distal reorganization and the NDH exhibiting stronger proximal stabilization-related responses.