Article

Postural reactions in healthy individuals in the seated position have previously
been described and have been shown to depend on the direction of the
perturbation; however the neck response following forward and backward
translations has not been compared. The overall objective of the present study
was to compare neck and trunk kinematic, kinetic and electromyographic (EMG)
stabilization patterns of seated healthy individuals to forward and backward
translations. Ten healthy individuals, seated on a chair fixed onto a movable
platform, were exposed to forward and backward translations (distance=0.15m, peak
acceleration=1.2m/s(2)). The head and trunk kinematics as well as the EMG
activity of 16 neck and trunk muscles were recorded. Neck and trunk angular
displacements were computed in the sagittal plane. The centers of mass (COMs) of
the head (HEAD), upper thorax (UPTX), lower thorax (LOWTX) and abdomen (ABDO)
segments were also computed. Moments of force at the C7-T1 and L5-S1 levels were
calculated using a top-down, inverse dynamics approach. Forward translations
provoked greater overall COM peak displacements. The first peak of moment of
force was also reached earlier following forward translations which may have
played a role in preventing the trunk from leaning backwards. These responses can
be explained by the higher postural threat imposed by a forward translation.
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Langue : ANGLAIS