External forces and torques generated by the brachiating White-handed gibbon (Hylobates lar)

We compared the kinetics of brachiation to bipedal walking and running. Gib bons use pectoral limbs in continuous contact with their overhead support a t slow speeds, but exhibit aerial phases (or ricochetal brachiation) at fas ter speeds. This basic interaction between limb and support suggests some a nalogy to walking and running. We quantified the forces in three axes and t orque about the vertical axis generated by a brachiating White-handed gibbo n (Hylobates lar) and compared them with bipedal locomotion. Handholds orie nted perpendicular to the direction of travel (as in ladder rungs) were spa ced 0.80, 1.20, 1.60, 1.72, 1.95, and 2.25 m apart. The gibbon proportional ly matched forward velocity to stride length. Handhold reaction forces rese mbled ground reaction forces of running humans except that the order of hor izontal braking and propulsion were reversed. Peak vertical forces in brach iation increased with speed as in bipedal locomotion. In contrast to bipeda lism, however, peak horizontal forces changed little with speed. Gait trans ition occurred within the same relative velocity range as the walk-run tran sition in bipeds (Froude number = 0.3-0.6). We oriented handholds parallel to the direction of travel (as in a continuous pole) at 0.80 and 1.60 m spa cings. In ricochetal brachiation, the gibbon generated greater torque with handholds oriented perpendicular as opposed to parallel to the direction of travel. Handhold orientation did not affect peak forces. The similarities and differences between brachiation and bipedalism offer insight into the u biquity of mechanical principles guiding all limbed locomotion and the dist inctiveness of brachiation as a unique mode of locomotion. (C) 2000 Wiley-L iss, Inc.