Performance and postural interactions during synchronous pointing and leg flexion.

Abstract

When several tasks are superimposed in a sequence, their associated postural dynamics interact, being either in opposition or in adequacy. The aim of this study was to test the influence of these postural interactions on the performance of each elementary task composing a sequence. Seven subjects performed the following experimental conditions: pointing to a target; right leg flexion; left leg flexion; right leg flexion and pointing (ipsilateral leg sequence, IS); and left leg flexion and pointing (contralateral leg sequence, CS). Movements were performed on a large force plate. Wrist and trunk accelerations were detected with accelerometers. Analysis of the postural dynamics along the lateral axis showed that the direction of the anticipatory postural adjustments (APA) for the pointing was the same as for the contralateral leg flexion, and that it was opposite to that for the ipsilateral leg flexion; that is, APA of the elementary tasks were compatible or in opposition. The performance of the pointing (maximal wrist velocity) was higher in the isolated pointing than in both sequences, and it was higher in CS than in IS. The performance of the leg flexion (maximal vertical velocity of the center of gravity) was higher in both sequences than in the isolated leg flexion, and body weight transfer toward the stance leg was facilitated in CS as compared with IS. These results show that the performance of a task depends whether it is done in isolation or in combination with an associated task, and that there exists favorable combinations for task performance. These results are interpreted in terms of compatibility between the postural dynamics associated with each task of the sequence.