Abstract
This study investigated external grip force vectors when grasping cylindrical handles of varying diameters. Forty-eight subjects (18 males and 30 females) grasped strain gage instrumented cylinders (2.54, 3.81, 5.08, 6.35, and 7.62 cm diameter) using a maximal voluntary exertion for a five-finger power grip and standardized postures. The third metacarpal bone was parallel to the axis of sensitivity to measure the force being exerted by the fingers against the palm. Each condition was presented to every subject in a random order and on a different day. The subjects were recruited from a manufacturing facility in the Midwest and consisted of a mixture of office and production personnel. Their ages ranged from 22 to 59 years. Hand length ranged from 15.2 cm to 20.9 cm. Two measurements were resolved into a force vector magnitude and associated force direction. On average, total grip force monotonically increased as handle diameter increased from 2.54 cm to 3.81 cm (30 N and 33 N increases for the left and right hands, respectively), and then decreased as diameter increased further. Average force direction for the resolved vector on the dominant hand was 57.5 degrees, 52.1 degrees, 46.7 degrees, 42.8 degrees and 36.3 degrees for handle diameters of 2.54 cm, 3.81 cm, 5.08 cm, 6.35 cm, and 7.62 cm respectively. The smallest contribution to the total force magnitude (39.3%) was produced in the direction where the fingertips opposed the thumb tip when the cylinder diameter was small. Conversely, the smallest contribution of the total force magnitude (42.1%) was produced in the direction where the fingertips opposed the palm when the cylinder diameter was large. These data are useful in the design of handles that require exertions to be directed in a specific direction relative to the hand.
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