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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.

A simple pendulum model is used to study how feedforward and feedback can be combined to control rhythmic limb movements. I show that a purely feedforward central pattern generator (CPG) is highly sensitive to unexpected disturbances. Pure feedback control analogous to reflex pathways can compensate for disturbances but is sensitive to imperfect sensors. I demonstrate that for systems subject to both unexpected disturbances and sensor noise, a combination of feedforward and feedback can improve performance. This combination is achieved by using a state estimation interpretation, in which a neural oscillator acts as an internal model of limb motion that predicts the state of the limb, and by using alpha-gamma coactivation or its equivalent to generate a sensory error signal that is fed back to entrain the neural oscillator. Such a hybrid feedforward/feedback system can optimally compensate for both disturbances and sensor noise, yet it can also produce fictive locomotion when sensory output is removed, as is observed biologically. CPG behavior arises due to the interaction of the internal model and a feedback control that uses the predicted state. I propose an interpretation of the neural oscillator as a filter for processing sensory information rather than as a generator of commands.

Experimental studies concerning the analysis of locomotor behavior in spinal cord injury research are widely performed in rodent models. The purpose of this study was to quantitatively evaluate the degree of functional recovery in reflex components and bipedal locomotor behavior of bonnet macaques (Macaca radiata) after spinal contusive injury. Six monkeys were tested for various reflex components (grasping, righting, hopping, extension withdrawal) and were trained preoperatively to walk in bipedal fashion on the simple and complex locomotor runways (narrow beam, grid, inclined plane, treadmill) of this investigation. The overall performance of the animals’ motor behavior and the functional status of limb movements during bipedal locomotion were graded by the Combined Behavioral Score (CBS) system. Using the simple Allen weight-drop technique, a contusive injury was produced by dropping a 13-g weight from a height of 30 cm to the exposed spinal cord at the T12-L1 vertebral level of the trained monkeys. All the monkeys showed significant impairments in every reflex activity and in walking behavior during the early part of the postoperative period. In subsequent periods, the animals displayed mild alterations in certain reflex responses, such as grasping, extension withdrawal, and placing reflexes, which persisted through a 1-year follow-up. The contused animals traversed locomotor runways—narrow beam, incline plane, and grid runways—with more steps and few errors, as evaluated with the CBS system. Eventually, the behavioral performance of all spinal-contused monkeys recovered to near-preoperative level by the fifth postoperative month. The findings of this study reveal the recovery time course of various reflex components and bipedal locomotor behavior of spinal-contused macaques on runways for a postoperative period of up to 1 year. Our spinal cord research in primates is advantageous in understanding the characteristics of hind limb functions only, which possibly mimic the human motor behavior. This study may be also useful in detecting the beneficial effect of various donor tissue–neuroprotective drugs on the repair of impaired functions in a bipedal primate model of spinal injury.

Increases in movement variability have previously been observed to be a hallmark property of cooraination changes between coupled oscillators that occur as movement frequency is scaled. Prior research on the walk-run transition in human locomotion has also demonstrated increases in variability around the transition region, supporting predictions of nonequilibrium phase transitions (Diedrich & Warren, 1995). The current study examined the coordinative patterns of both intra- and inter-limb couplings around the walk-run transition using two different temporal manipulations of locomotor velocity as a control parameter in healthy young participants (N = 11). Coordination variability did not increase before the transition. The nature of the change in continuous relative phase variability between gait modes was coupling-specific, and varying the time spent at each velocity did not have an overall effect on gait transition dynamics. Lower extremity inter-limb coordination dynamics were more sensitive to changes in treadmill velocity than intra-limb coordination. The results demonstrate the complexity of segmental coordination change in human locomotion, and question the applicability of dynamical bimanual coordination models to human gait transitions.

This study investigated developmental aspects of the acquisition of operant-trained bipedal (Bp) standing and Bp walking in the normally quadrupedal (Qp) juvenile Japanese monkey (M. fuscata). Four male monkeys (age: 1.6 to 2.4 years, body weight: 3.3 to 4.6 kg) were initially operantly trained to stand upright on a smooth floor and a stationary treadmill belt (width = 60 cm, walking length = 150 cm). They were then trained to walk bipedally on the moving treadmill belt (speed: 0.4–0.7 m/s). A regular training program (5 days/week; 30–60 min/day) was given to each monkey for the first 40 to 60 days, followed by less intensive training. After the beginning of locomotor training, upright postural stability and Bp walking capability were assessed kinematically for 592, 534, 526, and 537 days on monkeys A, B, C, and D, respectively. Left side- and back-views of the walking monkey were photographed (10 frames/s) and videotaped (250 frames/s). Stick figures of the head, body, and hindlimbs were drawn with reference to ink-marks positioned in front of the ear and over the pivot points of hindlimb joints. All kinematic data were digitized and analyzed using image-analyzing software. After sufficient physical growth and locomotor training, all the monkeys gradually acquired: (a) a more upright and a more stable posture with a constant body axis orientation during Bp locomotion; (b) a more stable and a stronger functional coupling between the body and hindlimb movements with a less anterior (A)-posterior (P) fluctuation of a body axis; (c) a smaller leftward (Lt)-rightward (Rt) displacement of the midline pelvic position, allowing the monkey to walk along a straight course; (d) a more coordinated relationship among hip-knee, knee-ankle, and ankle-metatarsophalangeal (MTP) joints; and finally (e) the acquisition of well-coordinated Bp walking even at high treadmill belt speeds up to 1.5 m/s. All of these results demonstrated the capability of the physically developing monkey to integrate the neural and musculoskeletal mechanisms required for sufficient coordination of upper (head, neck, trunk) and lower (hindlimbs) motor segments so that Bp standing and Bp walking could be elaborated.