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A pointing task was performed both while subjects stood beside and while subjects walked past targets that involved differing movement amplitudes and differing sizes. The hand kinematics were considered relative both to a fixed frame of reference in the movement environment (end effector kinematics) and to the subject's body (kinematics of the hand alone). From the former view, there were few differences between standing and walking versions of the task, indicating similarity of the kinematics of the hand. However, when the hand was considered alone, marked differences in the kinematics and spatial trajectories between standing and walking were achieved. Furthermore, kinematic analyses of the trunk showed that subjects used differing amounts of both flexion-extension and rotation movements at the waist depending on whether they were standing or walking as well as on the constraints imposed by target width and movement amplitude. The present results demonstrate the existence of motor equivalence in a combined upper and lower extremity task and that this motor equivalence is a control strategy to cope with increasing task demands. Given the complexity involved in controlling the arm, the torso, and the legs (during locomotion), the movements involved in the present tasks appear to be planned and controlled by considering the whole body as a single unit.

Locomotion generates a visual movement pattern characterized as optic flow. To explore how the locomotor adjustments are affected by this pattern, an experimental paradigm was developed to eliminate optic flow during obstacle avoidance. The aim was to investigate the contribution of optic flow in obstacle avoidance by using a stroboscopic lamp. Ten young adults walked on an 8m pathway and stepped over obstacles at two heights. Visual sampling was determined by a stroboscopic lamp (static and dynamic visual sampling). Three-dimensional kinematics data showed that the visual information about self-motion provided by the optic flow was crucial for estimating the distance from and the height of the obstacle. Participants presented conservative behavior for obstacle avoidance under experimental visual sampling conditions, which suggests that optic flow favors the coupling of vision to adaptive behavior for obstacle avoidance.

We studied the coordination of arm movements in standing persons who performed an out-of-phase arm-swinging task while stepping in place or while standing. The subjects were instructed to stop one of the arms in response to an auditory signal while trying to keep the rest of the movement pattern unchanged. A significant increase was observed in the amplitude of the arm that continued swinging under both the stepping and standing conditions. This increase was similar between the right and left arms. A dynamic model was developed including two coupled nonlinear van der Pol oscillators. We assumed that stopping an arm did not eliminate the coupling but introduced a new constraint. Within the model, superposition of two factors, a command to stop the ongoing movement of one arm and the coupling between the two oscillators, has been able to account for the observed effects. The model makes predictions for future experiments.

There have been few attempts to synthesize the knowledge gleaned from the study of cyclic human locomotion and, specifically, to determine whether there are general laws that describe or govern all such forms of locomotion. The purpose of this paper was to test the hypothesis that, when a human participant performs multiple trials of a given form of cyclic locomotion at a wide range of speeds (S) and without constraint on cycle rate (CR) or cycle length (CL), the relationships of CR vs. S and CL vs. S have the same basic characteristics as do those for any other form of cyclic locomotion. Data were gathered from published and unpublished sources. For each participant and form of locomotion, CR-vs.-S and CL-vs.-S relationships were plotted on a common scattergram with S on the abscissa and both CR and CL on the ordinate. Analysis of data collected on 49 participants and 12 forms of locomotion showed that, for every combination of participant and form of locomotion considered (excluding combinations involving simulated locomotion), the relationships of CR vs. S and CL vs. S had the same basic characteristics. These relationships were quadratic in form with CR-vs.-S concave upward and CL-vs.-S concave downward. The factor that made the greater contribution to increases in S was a function of S, with CL the primary factor at low S and CR the primary factor at high S. In short, the results obtained provided unequivocal support for the hypothesis of the study. The basic CR-vs.-S and CL-vs.-S relationships observed for forms of actual locomotion were also observed for some, but not all, of the forms of simulated locomotion examined.