My data sources are Humanscale 4/5/6 (Diffrient, Tilley, & Harman, 1981), Hand Anthropometry of U.S. Army Personnel (Greiner, 1991), and direct measurements of nine models of handguns (described in the next section).
Anthropometric measurements are made with the body in standard, reproducible positions. For the hand, this means that measurements are made with the hand extended and flat. However, when one places a handgun in the hand, with the center of the backstrap in the thumb crotch and the index finger wrapped around the trigger so that the pad of the outermost section (distal phalange) rests against the centerline of the trigger, both the first (distal) index finger joint and the second (medial) index finger joint must be bent. This bending decreases the effective length of the index finger and causes the adjacent flesh to fold and further decrease the effective length of the finger.
Because of these bends and folds, and the distance from the edge of the trigger to the centerline, an additional factor must be added to the distance between the thumb crotch and the first index finger joint. For my own hand, this additional factor is approximately .25 inch (6.4 mm). The resulting measure, which can be matched to corresponding handgun data, is designated trigger grip length. Although the .25-inch factor can be expected to vary with body size and gender, its variation should be small, and it should not affect trigger grip length appreciably. Trigger grip length as measured on a user is designated TGLU (illustrated in Figure 1).
Using data from Diffrient et al. (1981) and Greiner (1991), it is possible to correlate TGLU with the percentile of U.S. mal
Contact: Lois Smith
Human Factors and Ergonomics Society