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Developmental changes in upper limb muscle synergies during throwing: A comparison between preschoolers and schoolers

Hiroki Saito1,2,3, Ayane Kusafuka4, Taishi Okegawa3

  • 1Department of Physical Therapy, Tokyo University of Technology, Tokyo, Japan.

Iscience
|October 2, 2025
PubMed

Insights

Children refine throwing skills by developing more specialized muscle movements. Older children show improved accuracy and velocity due to fractionated muscle synergies, enhancing motor control.

Area of Science:

  • * Developmental motor control
  • * Biomechanics of human movement
  • * Pediatric neuromuscular adaptations

Background:

  • * Throwing is a fundamental motor skill that develops significantly during childhood.
  • * The underlying neuromuscular mechanisms driving this developmental refinement are not fully understood.
  • * Understanding muscle coordination is key to explaining improvements in throwing performance.

Purpose of the Study:

  • * To compare upper limb muscle synergies between preschool-aged and school-aged children during overarm throwing.
  • * To investigate how muscle recruitment strategies change with age and throwing proficiency.
  • * To identify developmental adaptations in neuromuscular control that enhance throwing performance.

Main Methods:

  • * Electromyographic activity from 16 upper limb muscles was recorded in 3-5 year olds (n=13) and 6-9 year olds (n=8).
  • * Ball kinematics were captured as participants threw balls toward a target.
  • * Non-negative matrix factorization (NMF) was used to extract and analyze muscle synergies for structure and sparseness.

Main Results:

  • * School-aged children demonstrated higher ball velocity and improved accuracy compared to preschoolers.
  • * Older children exhibited greater muscle synergy sparseness, indicating more selective muscle recruitment.
  • * Cluster analysis revealed a developmental shift from fewer, more generalized synergies in preschoolers to more numerous, specialized synergies in school-aged children.

Conclusions:

  • * Throwing performance in children is enhanced by the fractionation of muscle synergies into specialized components.
  • * This developmental adaptation improves energy transfer efficiency and control during the throwing motion.
  • * Findings underscore the importance of synergy fractionation as a key mechanism for refined motor skills in childhood development.

Keywords:
biological scienceshealth sciences

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