| The many degrees of freedom of the hand and arm afford the wide range and rich adaptability of human grip configurations in action. There have been several classification schemes of human grip configurations proposed but none are based on scaling laws of physical biology that are well established for other categorizations of fundamental physical activities, such as locomotion. We have examined the preferred human grip configurations used to displace cubes, that varied systematically in length (L), mass (M) and density (ML -3), to a new location. A total of 56 subjects aged 6--49 years were partitioned in four different experiments where different ranges of cubes dimension were displaced. Here we show that the body scaled equation K = log Lc + log Mc/( a + bLh + cMh), where Lh and Mh are the anthropometric measures of the hand length and mass and a, b and c are empirical constants, is the body-scaled information that predicts the grip configurations used to displace objects. Given that the hand grip configuration is organized prior to contact with the object, these findings suggest that information about the dynamic scaling relation is picked-up visually and organizes the many degrees of freedom of the hand-arm complex in the coordination of prehensile grip configurations. |
