Measuring postural sway in sitting: a new segmental approach.

Global measures of trunk sway are traditionally used even though the trunk comprises a multiple number of segments. The authors' aim was to measure the seated sway of typically developing children using a multisegment approach. Twenty typically developing children divided into 2 groups, older and younger than 10 years old, participated in this study. The children sat unsupported for 30 s while their posture and sway were quantified using stereophotogrammetry. The tendency in both age groups was to sit with a backward tilted pelvis and a kyphotic trunk. The sitting position was most varied in the younger group. Marker sway amplitude and velocity in sitting were age dependent, with reduced sway amplitude and velocity with increased age for all segments. Anteroposterior intersegmental angular sway was not age dependent. The difference in marker sway in the anteroposterior direction for the younger group appeared to result from an equally stable trunk supported on a less stable pelvis. Mediolateral marker sway and intersegmental angular sway showed a clearer age dependency. Trunk postural control does not appear to differ between children older and younger than 10 years old, but sagittal plane pelvic stability can explain the increased sway reported in younger children.