Parent handling of typical infants varies segmentally across development of postural control.

Although trunk muscles extend across multiple vertebral joints, recent motor control studies have shown that a top-down progression of trunk control in typical infants occurs incrementally, one segment at a time, until independent sitting. The current study merges this surprising developmental pattern with parent behavior by exploring the relationship between how parents hold their infant and the segmental level for which the infant exhibits postural control. We measured trunk control of 60 infants (1-8 months) via the segmental assessment of trunk control. Spontaneous parental hold and variability was recorded during repeated sitting and standing conditions. Parent hold correlated with infant level of control in both sitting and standing, providing evidence for a positive interaction between parent behavior and segmental trunk development.