Obstacle clearance and prevention from failing in the bipedally walking Japanese monkey, Macaca fuscata

Background: studies are needed which consider CNS-controlled strategies for accommodating perturbed bipedal (Bp) posture and walking. Objective: to demonstrate the suitability of the Japanese monkey, Macaca fuscata, for the above purpose. Setting and subjects: three adult monkeys were operantly trained to use Bp-walking on a moving treadmill belt. On one side of the belt, a rectangular adjustable-height obstacle confronted the ipsilateral leg every 4-6 steps, as determined by belt speed. Methods: animal posture and walking patterns were captured and digitized by two high-speed video systems. Frame-by-frame analyses of side- and back-view kinematics were obtained. Results: the monkeys learned quickly to proactively clear the in-coming obstacles by use of a flexible hip-knee-ankle flexion strategy. This featured an appropriate postural adjustment and leg trajectory. In cases where a monkey failed to clear the obstacle, it promptly adopted a defensive posture to avoid falling. There was then a quick return to a posture that allowed the resumption of a Bp gait. Conclusions: when Bp posture and gait are perturbed in a non-human primate model, the prompt adjustment of a flexible hip-knee-ankle flexion strategy and a defensive postural adjustment act together to prevent a fall and enable the speedy resumption of normal Bp posture and gait.