Power Grip Force Magnitude and Direction for Varying Cylindrical Handle Diameters and Hand Size

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, 3.8 1, 5.08, 6.35, and 7.62 cm diameter) using a maximal voluntary exertion for a five-fmger 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 of2.54 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 fmgertips 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.

A New Method for Estimating Biomechanical Loading in Grip

“…The average angle for the situation where the least friction existed (handle bare and oiled) increased from 24 to 37.2 degrees as load was increased. Edgren and Radwin (2000) strength data was used to estimate the tendon tension, which increased as cylinder size increased (Figure 5), even though the total force magnitude decreased for the larger handle diameters. At the largest handle diameters tendon tension decreased because the grip force magnitude was much smaller (57% of maximum).…”

“…In this manner, the relative flexor tendon tensions could be determined for any hand orientation and handle geometry. Data from Edgren and Radwin (2000), which was reported in grip force magnitude and force vector direction, was divided into lower, middle, and upper 33 percentiles by hand size and used as input into the biomechanical model. This was done to observe how flexor tendon force changes as handle diameter changes for maximal grip exertions.…”

“…Pheasant and O'Neil(l975) assumed that grip force was the sum of the components of the compressive forces uniformly distributed about the handle, however subsequent studies considering contribution of different parts of the finger (Amis, 1987) or different fingers (Kinoshita, et al, 1996;Radwin, et al, 1992) do not support this assumption. Edgren and Radwin (2000) considered grip force as a vector quantity having magnitude and direction by making two orthogonal force measurements and calculating the resultant vector. This procedure was used to test 61 employees force static maximal grip strength using a variety of cylinder diameters (25.4,38.1,50.8,63.5, and 76.2mm).…”