A paradigm to assess postural responses triggered by anteroposterior translations in healthy seated individuals

St-Onge, Nancy; Côté, Julie N.; Patenaude, Isabelle; Fung, Joyce

doi:10.1016/j.gaitpost.2009.06.007

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Volume 30, Issue 4 , Pages 417-423, November 2009

A paradigm to assess postural responses triggered by anteroposterior translations in healthy seated individuals☆

Nancy St-Onge
- Department of Exercise Science, Concordia University, 7141 Sherbrooke Street West, Montreal, QC, Canada H4B 1R6
- Constance-Lethbridge Rehabilitation Center, Center for Interdisciplinary Research in Rehabilitation of Greater Montreal (CRIR), 7005 de Maisonneuve Boulevard West, Montreal, QC, Canada H4B 1T3
- Jewish Rehabilitation Hospital Research Site of CRIR, 3205 Place Alton Goldbloom, Laval, QC, Canada H7V 1R2
- Corresponding author at: Department of Exercise Science, Concordia University, 7141 Sherbrooke St. West, Montreal, QC, Canada H4B 1R6. Tel.: +1 514 848 2424x5805; fax: +1 514 848 8681.
Julie N. Côté
- Jewish Rehabilitation Hospital Research Site of CRIR, 3205 Place Alton Goldbloom, Laval, QC, Canada H7V 1R2
- Department of Kinesiology and Physical Education, McGill University, 475 Pine Avenue West, Montreal, QC, Canada H2W 1S4
Isabelle Patenaude
- Jewish Rehabilitation Hospital Research Site of CRIR, 3205 Place Alton Goldbloom, Laval, QC, Canada H7V 1R2
- Department of Kinesiology and Physical Education, McGill University, 475 Pine Avenue West, Montreal, QC, Canada H2W 1S4
Joyce Fung
- Jewish Rehabilitation Hospital Research Site of CRIR, 3205 Place Alton Goldbloom, Laval, QC, Canada H7V 1R2
- School of Physical and Occupational Therapy, McGill University, 3654 Promenade Sir William Osler, Montreal, QC, Canada H3G 1Y5

Received 19 November 2007; received in revised form 2 June 2009; accepted 10 June 2009. published online 02 September 2009.

Abstract

Postural adjustments following mechanical perturbations have been studied in healthy seated humans. However, little is known on the minimal intensity that should be used to provoke a reaction. This knowledge could be essential to assess seated postural deficits in some pathological populations. The goal of the present study was to identify a low-intensity perturbation that could elicit postural reactions in healthy seated individuals. Six healthy participants sat on an adapted ergonomic chair fixed on a moveable support surface that was submitted to forward and backward translations. The head and trunk kinematics as well as the activity of sixteen neck and trunk muscles were recorded. The head, arm and trunk center of mass was computed using kinematics and standard anthropometric tables. We found that ramp displacements with an acceleration profile reaching a maximal value of 1.17m/s² elicited reliable kinematic and electromyographic reactions across participants. Head and trunk segments initially responded opposite to the direction of translation, then reversed direction. Median peak-to-peak angular displacements in the neck, head and trunk, respectively, reached 3.6°, 7.0° and 7.1° for forward translations, and 4.0°, 8.2° and 7.0° for backward translations. For forward translations, neck and trunk flexor muscles were activated first, followed by the extensor muscles, whereas for backward translations, extensor muscles were activated first, followed by flexors. Although this perturbation is of low-intensity compared to those typically used previously to evoke postural reactions, this stimulus is sufficient to elicit a reliable response. We suggest that such a perturbation could be used to assess the physical condition of individuals with neck injuries.