Grip width and the organization of force output.

The authors investigated the structure of force production and variability as a function of grip configuration and width during precision grasping. Variability was studied in absolute (standard deviation) and relative (coefficient of variation) terms; in addition, the authors used approximate entropy to examine regularity. In Experiment 1, the participants (N = 14) used a 2-digit grasp (thumb, index), whereas in Experiment 2, the participants (N = 11) used a 3-digit grasp (thumb, index, middle). The level and regularity of force increased with grip width. The amount of variability was least at narrow grip widths for 2-digit grasping and greatest at narrow grip widths for 3-digit grasping. That pattern of findings is not necessitated by the mechanical equilibrium of grasping; thus, it also reflected adaptive neural reorganization of force output to task demands.