Sit happens

Does sitting development perturb reaching development, or vice versa?

Regina T. Harbourne, Michele A. Lobo, Gregory M Karst, James Cole Galloway

Research output: Contribution to journalArticle

24 Citations (Scopus)

Abstract

We followed infants longitudinally while sitting and reaching skills developed. We used observational coding, motion analysis and EMG to describe changes over time. Reaching development was not perturbed by unstable sitting postural control. Variable postural strategies characterized early sitting, often causing falls. Infants appear to prioritize reaching for objects in spite of postural errors. The development of reaching and of sitting during the first year of life is typically studied as separate yet related behaviors. Interestingly, very soon after learning to reach, 4-7-month-old infants start coordinating their arms with their trunk and legs for sitting. In this longitudinal study, we focused, for the first time, on how infants learn to use their arms for the dual tasks of reaching for objects while providing arm support as they learn to sit. We hypothesized that the use of arms for support during sitting development would be a temporary perturbation to reaching and result in a nonlinear progression of reaching skill.Eleven infants were studied monthly from the time they began to prop sit to the time of sitting independence (5-8 months of age). Behavioral coding, kinematics, and electromyography (EMG) characterized reaching and posture while infants sat as independently as possible. Results revealed significant changes across time in trunk movement and hand use as infants transitioned through three stages of sitting: with arm support, sitting briefly without arm support, and sitting independently. Infants used their hands more for contacting objects and less for posture support linearly across time. In contrast, changes in posture control as indicated by pelvis and trunk movement demonstrated a U-shaped curve with more movement of these two body segments during the middle stage of sitting than in the first or last stage. During the middle stage of sitting infants reached persistently even though posture control, measured by pelvis and trunk movement, appeared to be significantly challenged. Muscle activation consisted of tonic and variable combinations of muscle pairings in early sitting. As infants progressed to sitting without hand support, variable but successful strategies utilizing lower extremity muscles in a tight linkage with reach onset emerged to provide prospective control for reaching. Our findings support the contention that reaching both drives the development of sitting in infancy as well as perturbs sitting posture, factoring into the assembly of the complex dual sit-reach behavior that supports and expands flexible interaction with the environment.

Original languageEnglish (US)
Pages (from-to)438-450
Number of pages13
JournalInfant Behavior and Development
Volume36
Issue number3
DOIs
StatePublished - May 14 2013

Fingerprint

Posture
Arm
Hand
Electromyography
Pelvis
Muscles
Biomechanical Phenomena
Longitudinal Studies
Lower Extremity
Leg
Learning

Keywords

  • Infant development
  • Reaching
  • Sitting

ASJC Scopus subject areas

  • Developmental and Educational Psychology

Cite this

Sit happens : Does sitting development perturb reaching development, or vice versa? / Harbourne, Regina T.; Lobo, Michele A.; Karst, Gregory M; Galloway, James Cole.

In: Infant Behavior and Development, Vol. 36, No. 3, 14.05.2013, p. 438-450.

Research output: Contribution to journalArticle

Harbourne, Regina T. ; Lobo, Michele A. ; Karst, Gregory M ; Galloway, James Cole. / Sit happens : Does sitting development perturb reaching development, or vice versa?. In: Infant Behavior and Development. 2013 ; Vol. 36, No. 3. pp. 438-450.
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