Fig. 3.

Time courses of the ground reaction force components F at the second leg during slow locomotion (10 cm/s) of Cupiennius salei. Forces ± SD (shaded; N = 4; n > 18) are normalized to a body mass of 3 g. a–c Components (X anteriad, Y mediad, Z dorsad) with respect to body orientation (global system; X, Y, Z). The reaction force has only minor anteriad and mediad components. d–f Components as calculated for a co-ordinate system (x anteriad, y ventrad, z proximad) with the z-axis parallel to the metatarsus and the y-axis within in the plain of the tibia–metatarsus joint (local system). Whereas the anteriad component is small due to the oblique position of the metatarsus, there is a considerable negative ventrad component which must be balanced by flexor activity at the tibia–metatarsus joint (Data: Brüssel 1987; Barth 2002)