Figure 2.

Representative examples of digit force vectors (A) and displacement of the points of digit force application on the sensor surface (B). The handle (total weight 15.71 N) was maintained vertically at rest in the air at three different torques exerted on the handle, −1.5 Nm, 0 Nm (no torque), and 1.5 Nm. The torques were applied to the handle about an axis perpendicular to the plane of the page. The subjects were instructed to exert minimal force on the handle. The positive and negative direction of the torque refers to the resistive torque exerted by the subject (which is in the opposite direction to the external torque due to the loading). The supination torque efforts are negative and the pronation torque efforts are positive.

(A) The thin arrows originating at the five force sensors represent the corresponding digit forces; they are in proportion to force magnitude and along the line of force action. The two thick curved arrows indicate the subject efforts either in supination (−1.5 Nm, the arrow on the left) or in pronation (1.5 Nm, on the right), group average data. In this and future references, if not mentioned otherwise, the sensors are covered by 100-grit sandpaper (friction coefficient ≈ 1.40–1.52).

(B) Displacement of the point of application of digit forces in the vertical direction at the various torque levels. The results are for an individual subject (average of ten trials). Note that the displacement can be as large as 10 mm. (Adapted by permission from V.M. Zatsiorsky, F. Gao, and M.L. Latash. Finger force vectors in multi-finger prehension. Journal of Biomechanics, 2003, 36:1745–1749).