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Published on: March 4, 2014
Spatially Specific Changes in Infants' Muscle Coactivity as They Learn to Reach
John P Spencer1, Esther Thelen2
1Department of Psychology University of Iowa.
Insights
Infants develop new muscle coordination patterns when learning to reach for objects between 3 and 5 months. This transition involves significant changes in how muscles like the biceps and deltoids work together.
Area of Science:
- Developmental motor control
- Infant motor development
- Biomechanics of reaching
Background:
- Infants develop the ability to reach and touch objects between 3 and 5 months of age.
- Motor control involves complex muscle coordination.
- Understanding the developmental trajectory of motor skills is crucial.
Purpose of the Study:
- To investigate changes in muscle coactivity during the transition to reaching in infants.
- To analyze the kinematic and electromyographic data associated with prereaching and reaching movements.
Main Methods:
- Longitudinal observation of 4 infants from 3 to 52 weeks.
- Collection of hand kinematics for prereaching and reaching movements.
- Electromyographic (EMG) recordings of trapezius, deltoid, biceps, and triceps muscles.
Main Results:
- Before reaching, infants used biceps and triceps for hand movements towards objects.
- After the transition to reaching, infants utilized trapezius and deltoid muscles.
- Complex muscle combinations were observed in later stages, particularly with extended arms.
Conclusions:
- Infants exhibit a significant shift in muscle recruitment patterns during the development of reaching.
- The transition to reaching involves a refinement of motor control strategies.
- Despite similar spatial hand movements, the underlying muscle synergies change dramatically.
Abstract:
Infants first reach out and touch objects between the ages of 3 and 5 months. This article reports changes in muscle coactivity associated with this transition. A group of 4 infants were observed weekly from 3 to 30 weeks and every 2 weeks from 30 to 52 weeks. Hand kinematics of both prereaching and reaching movements were collected, as was electromyographic activity from the trapezius, deltoid, biceps, and triceps. Before infants first reached for toys presented at midline, they used biceps and triceps to move their hands near the toy in front of them and 45° to the side of midline. After the transition, they used trapezius and deltoid to move the hand toward the toy and combinations of multiple muscles when their arms were high and extended near the toy. Thus, infants showed a dramatic change in which muscles worked together across the transition to reaching, even though their hands moved in similar spatial regions.
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