title: Direction-dependent neck and trunk postural reactions during sitting.
abstract: 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.
authors.affiliation: Department of Exercise Science, Concordia University, 7141 Sherbrooke St. West, Montreal, QC, Canada. nancy.st-onge@concordia.ca
authors.forename: Nancy
authors.initials: N
authors.lastname: St-Onge
authors.forename: Julie N
authors.initials: JN
authors.lastname: Côté
authors.forename: Richard A
authors.initials: RA
authors.lastname: Preuss
authors.forename: Isabelle
authors.initials: I
authors.lastname: Patenaude
authors.forename: Joyce
authors.initials: J
authors.lastname: Fung
mesh_terms: D000005:Abdomen / Q000502:physiology*; D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009068:Movement / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D009333:Neck / Q000502:physiology*; D004856:Postural Balance / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology; D013909:Thorax / Q000502:physiology*; D055815:Young Adult