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A kinematic and electromyographic analysis of the development of sitting posture in infants
R T Harbourne1, C Giuliani, J M Neela
1Meyer Rehabilitation Institute, University of Nebraska Medical Center, Omaha 68198-5450.
Insights
Infants develop better sitting posture control as they mature, showing decreased trunk movement and more consistent muscle activation patterns. This improvement is linked to specific muscle synergies, particularly involving the lumbar paraspinals and hamstrings or quadriceps.
Area of Science:
- Developmental motor control
- Infant biomechanics
- Postural stability
Background:
- Independent sitting is a crucial developmental milestone.
- Understanding the development of posture control is key to identifying potential delays or impairments.
Purpose of the Study:
- To describe the development of posture control in infants sitting independently.
- To analyze postural responses to natural perturbations in relation to sitting development stages.
Main Methods:
- Seven infants (2-5 months) were tested at two stages of sitting development.
- Postural responses to trunk support removal were recorded using video and electromyography (EMG).
- Kinematic (trunk displacement, velocity, curvature) and EMG variables (muscle activation patterns) were analyzed.
Main Results:
- Anterior trunk displacement and velocity significantly decreased between sitting development stages.
- Muscle activation patterns showed reduced variability and the emergence of postural synergies in later stages.
- Lumbar paraspinals, hamstrings, and quadriceps were most active; common synergies involved lumbar paraspinals with hamstrings or quadriceps.
Conclusions:
- Trunk displacement and velocity decrease as infants develop independent sitting posture.
- The emergence and preferred use of specific muscle synergies (e.g., lumbar paraspinal-hamstring) are related to improved sitting posture control.
Abstract:
This study was designed to describe the development of posture control in sitting in response to a natural perturbation. Seven normal infants 2 to 5 months of age were tested at two stages of independent sitting development. Trunk support was removed from infants while sitting erect and the postural responses were videotaped and EMG recorded from the upper trunk extensors, lumbar paraspinals, gluteus maximus, rectus femoris, hamstrings, and abdominals. Kinematic variables (trunk displacement, trunk velocity, trunk curvature) and an EMG variable (pattern of muscle activation) were analyzed with computer programs. Between Stages 1 and 2 of sitting development, anterior trunk displacement and velocity decreased significantly, although the trunk extension curve did not change significantly. Infants had variable muscle responses during Stage 1; however, during Stage 2 EMG analysis revealed less variability and the emergence of postural synergies. Overall, lumbar paraspinals, hamstrings, and quadriceps were the muscles most frequently active during the postural response. Each subject had a preferred synergy, with the most common synergies being a lumbar paraspinal-hamstring synergy and a lumbar paraspinal-quadriceps synergy. These data provide evidence that trunk displacement and trunk velocity decrease in infants develop independent sitting posture, and these variables may be used to measure improvement in sitting control. We suggest that the control of sitting posture is related to the emergence and preferred use of the paraspinal-hamstring and paraspinal-quadriceps synergies.