Grip posture and forces during holding cylindrical objects with circular grips.

Individual finger position and external grip forces were investigated while subjects held cylindrical objects from above using circular precision grips. Healthy females (n = 11) and males (n = 15) lifted cylindrical objects of various weights (0.5, 1.0 and 2.0 kg), and varied diameters (5.0, 7.5 and 10.0 cm) using the 5-finger grip mode. The effects of 4-, 3- and 2-finger grip modes in the circular grip were also investigated. Individual finger position was nearly constant for all weights and for diameters of 5.0 and 7.5 cm. The mean angular positions for the index, middle, ring and little fingers relative to the thumb were 98 degrees, 145 degrees, 181 degrees, and 236 degrees, respectively. At the 10-cm diameter, the index and middle finger positions increased, while the ring and little finger positions decreased. There were no differences in individual finger position with regard to gender, hand dimension, or hand strength. Total grip force increased with weight, and at diameters greater or lesser than 7.5 cm. Total grip force also increased as the number of fingers used for grasping decreased. Although the contribution of the individual fingers to the total grip force changed with weight and diameter, the thumb contribution always exceeded 38% followed by the ring and little fingers, which contributed approximately 18-23% for all weights and diameters. The contribution of the index finger was always smallest (> or = 11%). There was no gender difference for any of the grip force variables. The effects of hand dimension and hand strength on the individual finger grip forces were subtle.