Influence of surface curvature and pinch span on the maximal force exertion of pinch grip: a prospective cohort study

This study investigated how the pinch surface curvature and pinch span influence the maximal voluntary pinch grip forces (MVFs) for different pinch types. Twelve male participants (age range: 22–34) underwent MVF measurements using a pinch grip on a dynamometer with six interchangeable attachment surfaces. They were randomly assigned to either a concave or convex handle group, each tested with three pinch spans (3, 5, and 7 cm) using a custom-designed dynamometer (Model T.K.K. 1269m and TSA-210; Takei Scientific Instruments Co., Ltd.). The pinch type was controlled as a tip, three-jaw, or key pinch, and both the dominant and non-dominant hands were examined. After completing the trials for each condition, participants rated their overall comfort, perceived fit, and perceived difficulty on a 5-point rating scale. We demonstrated that the concave surface was associated with greater MVFs than the convex surface ( p < 0.01). However, the difference in MVF was insignificant when the pinch span was increased to 7 cm. The key pinch and dominant hand showed higher MVFs, better fit, and lower difficulty than their counterparts (key pinch: p s < 0.05; dominant hand: p s < 0.01). This study provides evidence on the design of pinch surface curvature and span that can effectively enhance MVF performance under varying pinch span conditions.