Article

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 1.17 m/s(2) 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 degrees, 7.0 degrees and 7.1 degrees for forward translations, and
4.0 degrees, 8.2 degrees and 7.0 degrees 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.

Langue : ANGLAIS