Task demands modulate distal limb handedness: A comparative analysis of prehensile synergies of the dominant and non-dominant hand

The dynamic dominance hypothesis of handedness suggests a distinct control strategy for the dominant and the non-dominant limb. The hypothesis demonstrated that the dominant proximal limb is tuned for optimal trajectory control while the non-dominant limb is tuned for a stable grasp. Whether the hypothesis can be extended to distal segments like fingers, especially during a five-fingered grasp, has been studied little. To examine this, an attempt was made to compare the prehensile synergies and force magnitudes of the dominant (DOM) and non-dominant hands (NDOM) during a 5-fingered prehension task. Participants traced a trapezoidal and inverse trapezoidal path with their thumbs on a sliding platform while holding a handle in static equilibrium. The DOM hand performed better only in the inverse trapezoid condition, exhibiting a reduced grip force and increased synergy index aligning with the dynamic dominance hypothesis. No differences were observed for the trapezoid condition, likely due to reduced task demands. The study also explored changes in anticipatory synergy adjustments between the DOM and NDOM hands, but the differences were non-significant. Overall, the DOM hand demonstrated better force coordination than the NDOM hand in challenging conditions. Applications of the study in the objective assessment of handedness were proposed.