Does an additional load modify the Anticipatory Postural Adjustments in gait initiation?

The objective of the study was to examine whether and how an additional load affects the Anticipatory Postural Adjustments (APA) in gait initiation in able-bodied individuals. Nineteen healthy participants initiated gait at a self-selected speed in two conditions: unloaded and with an overload of 15% body weight. The APA duration, the forward impulse of the APA and the duration of gait initiation increased significantly with the overload, while the other variables did not change. These results indicate that, during gait initiation with overload, able-bodied subjects modulate the APA duration to produce a higher forward impulse in order to achieve the steady-state gait at the end of the first step. These findings could have implications in clinical practice where overloading could be used to improve the gait initiation in pathologic patients. Further investigations are needed to confirm this suggestion.

Pelvis morphology, trunk posture and standing imbalance and their relations to the Cobb angle in moderate and severe untreated AIS.

Adolescent idiopathic scoliosis (AIS) is the most common form of scoliosis and usually affects young girls. Studies mostly describe the differences between scoliotic and non-scoliotic girls and focus primarily on a single set of parameters derived from spinal and pelvis morphology, posture or standing imbalance. No study addressed all these three biomechanical aspects simultaneously in pre-braced AIS girls of different scoliosis severity but with similar curve type and their interaction with scoliosis progression. The first objective of this study was to test if there are differences in these parameters between pre-braced AIS girls with a right thoracic scoliosis of moderate (less than 27°) and severe (more than 27°) deformity. The second objective was to identify which of these parameters are related to the Cobb angle progression either individually or in combination of thereof. Forty-five scoliotic girls, randomly selected by an orthopedic surgeon from the hospital scoliosis clinic, participated in this study. Parameters related to pelvis morphology, pelvis orientation, trunk posture and quiet standing balance were measured. Generally moderate pre-brace idiopathic scoliosis patients displayed lower values than the severe group characterized by a Cobb angle greater than 27°. Only pelvis morphology and trunk posture were statistically different between the groups while pelvis orientation and standing imbalance were similar in both groups. Statistically significant Pearson coefficients of correlation between individual parameters and Cobb angle ranged between 0.32 and 0.53. Collectively trunk posture, pelvis morphology and standing balance parameters are correlated with Cobb angle at 0.82. The results suggest that spinal deformity progression is not only a question of trunk morphology distortion by itself but is also related to pelvis asymmetrical bone growth and standing neuromuscular imbalance.

Target size modifies anticipatory postural adjustments and subsequent elementary arm pointing.

We herein studied whether arm-pointing movements from an upright posture (i.e. Belenkii's paradigm) toward various targets demanding a low degree of precision could influence associated anticipatory postural adjustments (APAs) and subsequent arm movements. Six subjects were asked to use their right arm to point (without finger touch) to targets of 2, 4 and 8 cm in diameter (respectively, D2, D4 and D8). APAs were measured by recording the electromyographic activity of the right anterior deltoid and biceps femoris, as well as the kinematics of the right arm. Longer APA durations and lower values for the ratio between acceleration duration and total duration of the focal movement were observed for D4 compared to D2 and D8, whereas precision was constant across all three targets. Thus, the medium target seemed to engender an optimum motor strategy for accomplishing the accuracy and velocity requirements of the task. These results emphasize that subjects build perceptual representations of their environment as well as representations of the actions to be produced. We suggest that, even in this simple movement traditionally studied from a biomechanical perspective, APAs function not only to compensate for perturbations to equilibrium, but also reflect a cognitive representation of the precision requirements of the task.