This article focuses on postural anticipation and multi-joint coordination during locomotion in healthy and autistic children. Three questions were addressed. (1) Are gait parameters modified in autistic children? (2) Is equilibrium control affected in autistic children? (3) Is locomotion adjusted to the experimenter-imposed goal? Six healthy children and nine autistic children were instructed to walk to a location (a child-sized playhouse) inside the psychomotor room of the pedopsychiatric centre located approximately 5 m in front of them. A kinematic analysis of gait (ELITE system) indicates that, rather than gait parameters or balance control, the main components affected in autistic children during locomotion are the goal of the action, the orientation towards this goal and the definition of the trajectory due probably to an impairment of movement planning.

The aim of the present investigation was to see whether the kinematic synergy responsible for equilibrium control during upper trunk movement was preserved in absence of gravity constraints. In this context, forward trunk movements were studied during both straight-and-level flights (earth-normal gravity condition: normogravity) and periods of weightlessness in parabolic flights (microgravity). Five standing adult subjects had their feet attached to a platform, their eyes were open, and their hands were clasped behind their back. They were instructed to bend the trunk (the head and the trunk together) forward by approximately 35 degrees with respect to the vertical in the sagittal plane as fast as possible in response to a tone, and then to hold the final position for 3 s. The initial and final anteroposterior center of mass (CM) positions (i.e., 200 ms before the onset of the movement and 400 ms after the offset of the movement, respectively), the time course of the anteroposterior CM shift during the movement, and the electromyographic (EMG) pattern of the main muscles involved in the movement were studied under both normo- and microgravity. The kinematic synergy was quantified by performing a principal components analysis on the hip, knee, and ankle angle changes occurring during the movement. The results indicate that 1) the anteroposterior position of the CM remains minimized during performance of forward trunk movement in microgravity, in spite of the absence of equilibrium constraints; 2) the strong joint coupling between hip, knee, and ankle, which characterizes the kinematic synergy in normogravity and which is responsible for the minimization of the CM shift during movement, is preserved in microgravity. It represents an invariant parameter controlled by the CNS. 3) The EMG pattern underlying the kinematic synergy is deeply reorganized. This is in contrast with the invariance of the kinematic synergy. It is concluded that during short-term microgravity episodes, the kinematic synergy that minimizes the anteroposterior CM shift is surprisingly preserved due to fast adaptation of the muscle forces to the new constraint.

The aim of the present investigation was to study the adaptation of the kinematic synergy responsible for equilibrium control during upper trunk movements to a 10-kg load added to the subject's shoulders. Five adult subjects were asked to bend their upper trunk forward to an angle of 35 degrees and then to hold the final position for 3 s, first without any load and then with a 10-kg load fixed to their shoulders. The final anteroposterior CM positions 400 ms after the movement offset, the time course of the anteroposterior center of mass (CM) shift during the movement, the EMG pattern of the main muscles involved in the movement and the initial CP shift were studied under both unloaded and loaded conditions. The kinematic synergy was quantified by performing a principal components analysis on the hip, knee and ankle angle changes occurring during the movement. The results indicate that: (1) the final anteroposterior position of the CM changed little if at all in the presence of the additional load, and that the anteroposterior CM shift was minimized throughout the duration of the movement; (2) the kinematic synergy was still characterized, in the presence of the additional load, by a strong coupling between the angle changes, as indicated by the fact that the first principal component (PC1) accounted for more than 99% of the hip, knee and ankle joint movements. A change was observed, however, in the ratio between the angles: the ankle extension increased, thus compensating for the additional theoretical forward CM shift that the additional load could be expected to cause; (3) the lack of change in the initial backward CP shift observed under loaded condition as well as the lack of change of the initial agonist EMG bursts suggest that the initial feedforward control of the kinematic synergy was not affected in the presence of the additional load. An increase in the antagonist bursts, presumably reflecting an adaptation of the kinematic synergy, was observed during the late phase of the movement; and (4) it is concluded that the adaptation of the kinematic synergy to the load was due to a specific change in the feedback control during the braking phase of the movement which presumably increases the ankle joint extension and consequently causes an increased backward shift of the hip which compensates for the forward shift due to the load.

No abstract