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The development toward stereotypic arm kinematics during reaching in the first 3 years of life
1Department of Neurology, University of Tübingen, Germany. Konczak@uni-duesseldorf.de
Insights
Infant reaching movements mature later than expected, with adult-like coordination patterns emerging around the second year of life. This study tracks the development of multijoint coordination in infants up to three years old.
Area of Science:
- Developmental neuroscience
- Motor control
- Human kinematics
Background:
- Infant reaching is a fundamental motor skill.
- Understanding the timeline of motor development is crucial for identifying developmental milestones.
Purpose of the Study:
- To determine when infants achieve adult-like multijoint coordination patterns.
- To analyze the relationship between hand trajectory and proximal joint motion in infants.
Main Methods:
- Longitudinal recording of reaching movements in nine infants from 5 months to 3 years.
- Analysis of hand and proximal joint (shoulder, elbow) trajectories.
- Examination of temporal coordination between arm segments.
Main Results:
- Most kinematic parameters reach adult-like levels after 2 years of age.
- Infants develop velocity profiles with minimal force reversals.
- Stable interjoint coordination emerges between 12-15 months and develops through 3 years.
Conclusions:
- Development of adult-like multijoint coordination in reaching is a prolonged process.
- Stereotypical kinematic motor patterns are not established before 2 years of age, despite early object grasping ability.
Abstract:
We recorded reaching movements from nine infants longitudinally from the onset of reaching (5th postnatal month) up to the age of 3 years. Here we analyze hand and proximal joint trajectories and examine the emerging temporal coordination between arm segments. The present investigation seeks (a) to determine when infants acquire consistent, adult-like patterns of multijoint coordination within that 3-year period, and (b) to relate their hand trajectory formation to underlying patterns of proximal joint motion (shoulder, elbow). Our results show: First, most kinematic parameters do not assume adult-like levels before the age of 2 years. At this time, 75% of the trials reveal a single peaked velocity profile of the hand. Between the 2nd and 3rd year of life, "improvements" of hand- or joint-related movement units are only marginal. Second, infant motor systems strive to obtain velocity patterns with as few force reversals as possible (uni- or bimodal) at all three limb segments. Third, the formation of a consistent interjoint synergy between shoulder and elbow motion is not achieved within the 1st year of life. Stable patterns of temporal coordination across arm segments begin to emerge at 12-15 months of age and continue to develop up to the 3rd year. In summary, the development toward adult forms of multijoint coordination in goal-directed reaching requires more time than previously assumed. Although infants reliably grasp for objects within their workspace 3-4 months after the onset of reaching, stereotypic kinematic motor patterns are not expressed before the 2nd year of life.