Direction-dependent neck and trunk postural reactions during sitting |
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| Authors: | Nancy St-Onge Julie N Côté Richard A Preuss Isabelle Patenaude Joyce Fung[Author vitae] |
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| Institution: | aDepartment of Exercise Science, Concordia University, 7141 Sherbrooke St. West, Montreal, QC, Canada H4B 1R6;bConstance-Lethbridge Rehabilitation Center, Montreal Center for Interdisciplinary Research in Rehabilitation (CRIR), 7005 Maisonneuve W., Montreal, QC, Canada H4B 1T3;cFeil & Oberfeld/CRIR Research Centre, Jewish Rehabilitation Hospital, 3205 Place Alton Goldbloom, Laval, QC, Canada H7V 1R2;dDepartment of Kinesiology and Physical Education, McGill University, 475 Pine Avenue West, Montreal, QC, Canada H2W 1S4;eSchool of Physical and Occupational Therapy, McGill University, 3654 Promenade Sir William Osler, Montreal, QC, Canada H3G 1Y5 |
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| 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 = 0.15 m, peak acceleration = 1.2 m/s2). 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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| Keywords: | Postural reactions Muscle activity Kinematics Kinetics |
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