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Development of proximal arm muscle control during reaching in young infants: from variation to selection
Hanneke Bakker1, Victorine B de Graaf-Peters, Leo A van Eykern
1Department Paediatrics - Developmental Neurology, University Medical Center Groningen, University of Groningen, Hanzeplein 1, 9713 GZ Groningen, The Netherlands.
Insights
Between 4 and 6 months, infants develop dominant biceps brachii (BB) muscle activity for reaching. This prime mover emergence correlates with more efficient infant reaching movements.
Area of Science:
- Developmental motor control
- Infant biomechanics
- Neuroscience of movement
Background:
- Reaching movements are initiated by prime mover muscle activation.
- Understanding infant motor development is crucial for identifying developmental milestones.
Purpose of the Study:
- To investigate the relationship between prime mover activity and reaching kinematics in infants.
- To examine changes in motor control and movement efficiency between 4 and 6 months of age.
Main Methods:
- Electromyography (EMG) and kinematic analysis of reaching movements in 14 typically developing infants.
- Assessment in supine and supported sitting positions at 4 and 6 months.
- Recorded EMG of deltoid, pectoralis major, biceps brachii (BB), and triceps brachii.
Main Results:
- Prime mover muscle use was variable at 4 months but showed a dominance of BB at 6 months.
- Infant reaching kinematics showed a decrease in movement units (MUs) and an increase in the relative proportion of the transport MU with age.
- BB prime mover dominance at 6 months was associated with a larger transport MU.
Conclusions:
- A dominance of biceps brachii (BB) as the prime mover emerges between 4 and 6 months in infants.
- This developmental shift in prime mover activity is linked to more efficient reaching characteristics in infants.
Unlabelled:
Reaching movements are initiated by activity of the prime mover, i.e. the first activated arm muscle. We aimed to investigate the relationship between prime mover activity and kinematics of reaching in typically developing (TD) infants in supine and sitting position. Fourteen infants were assessed at 4 and 6 months during reaching in supine and supported sitting. Kinematics and EMG-activity of deltoid, pectoralis major, biceps (BB) and triceps brachii were recorded. Kinematic analysis focused on number of movement units (MUs) and transport MU (MU with longest duration). Prime mover use was variable, but at 6 months a dominance of BB emerged in both testing conditions. Kinematics were also variable, but with increasing age the number of MU decreased and the relative proportion of the transport MU increased. BB as prime mover at 6 months was related to a larger transport MU.
Conclusion:
Between 4 and 6 months BB prime mover dominance emerges which is related to relatively efficient reaching characteristics.
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