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Quantifying Learning in Young Infants: Tracking Leg Actions During a Discovery-learning Task
Published on: June 1, 2015
Adaptive Dynamics of the Leg Movement Patterns of Human Infants: I. The Effects of Posture on Spontaneous Kicking
J. L. Jensen1, K. Schneider, B. D. Ulrich
1Department of Exercise and Movement Science, University of Oregon, Eugene, OR 97403, USA. JLJ@OREGON.UOREGON.EDU
Insights
Infants adapt leg movements to posture, with upright positions increasing gravitational resistance and muscle coordination. This demonstrates how early motor control is influenced by gravity and limb dynamics.
Area of Science:
- Developmental neuroscience
- Motor control
- Infant biomechanics
Background:
- Infant motor development involves adapting movements to postural changes.
- Understanding how gravity influences early motor patterns is crucial.
Purpose of the Study:
- To investigate how 3-month-old infants adjust leg movement kinematics across different postures (supine, angled, vertical).
- To analyze the contributions of muscular and nonmuscular forces to infant leg movements in varying gravitational contexts.
Main Methods:
- Comparison of leg kick kinematics in infants across three distinct postural conditions.
- Assessment of muscular and nonmuscular force contributions to limb trajectory.
- Analysis of joint range of motion and muscle torque correlations.
Main Results:
- Upright postures significantly increased gravitational resistance at the hip compared to supine.
- Vertical posture led to reduced hip range of motion and increased synchronous hip and knee flexion/extension.
- Higher correlation between hip and knee muscle torques was observed in the vertical posture.
Conclusions:
- Infant motor systems show sensitivity to gravitational context, altering leg movement dynamics.
- Intrinsic limb dynamics, influenced by anatomical and energetic constraints, play a role in coordinating infant limb movements.
- Postural changes necessitate adjustments in muscle activation and joint coordination for effective locomotion.
Abstract:
This is the first of two articles in which we describe how infants adapt their spontaneous leg movements to changes in posture or to elicitation of behaviors by a mechanical treadmill. In this article, we compare the kinematics of kicks produced by 3-month-old infants in three postures, supine, angled (45 degrees ), and vertical, and examine the changes in muscular and nonmuscular force contributions to limb trajectory. By manipulating posture we were able to assess the sensitivity of the nascent motor system to changes in the gravitational context. The postural manipulation elicited a distinct behavioral and dynamic effect. In the more upright postures, gravitational resistance to motion at the hip was 4 to 10 times greater than resistance met in the supine posture, necessitating larger muscle torques to drive hip flexion. Kicks produced in the vertical posture showed a reduction in hip joint range of motion and an increase in synchronous joint flexion and extension at the hip and knee. At the same time, hip and knee muscle torques were also more highly correlated in kicks performed in the vertical than in the supine or angled posture. This increased correlation between muscle torques at the hip and knee implicates anatomical and energetic constraints-the intrinsic limb dynamics-in creating coordinated limb behavior out of nonspecific muscle activations.
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