VARIABILITY OF NEUROMUSCULAR MECHANISMS AND GRAVITATIONAL TORQUE IN THE INITIAL STAGES OF INDEPENDENT GAIT IN TYPICALLY DEVELOPING CHILDREN

Paula Silva de Carvalho Chagas
Department of Physical Therapy, School of Medicine, UFJF

Marisa Cotta Mancini
Department of Occupational Therapy, Federal University of Minas Gerais State (UFMG)

S?rgio Teixeira da Fonseca
Department of Physical Therapy, Federal University of Minas Gerais State (UFMG)

Ana Paula Bensemann Gontijo
Department of Physical Therapy, Federal University of Minas Gerais State (UFMG)

Raquel Etrusco Luz
Occupational Therapist

Juliana Mambrini
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     Last modified: March 1, 2007

Abstract
INTRODUCTION: The use of neuromuscular mechanisms has been considered an essential component in the process of motor acquisition. In general, periods of variability are important because they characterize an exploration phase of the different systems, making possible the selection of future adaptive strategies.
AIM: Evaluate the longitudinal changes of the variability distribution of the co-contraction indexes (CCI) and the gravitational torque (mLg), within-children and between children, during the period of two months after gait acquisition in typical children.
METHODS: Twelve children with typical motor development were followed during two months after onset of independent gait. Quantification of the EMG signals of six muscles in the right lower limb allowed the calculation of the CCI considering pairs of antagonistic muscles, representing the hip, knee and ankle joints, and the sum of the CCIs yield a total index. The initial period of gait acquisition was documented by the standardized test Alberta Infant Motor Scale, and the anthropometric measurements were transformed into gravitational torque (mLg) for the stance and swing phases of gait. For the data analysis the normalized variable was used (CCI/mLg). Statistical analyses included a regression model for longitudinal data to evaluate how was the variability within-children and between children of the variables mentioned above, in both phases of gait.
RESULTS: The regression model demonstrated significant differences between infants in the CCI/mLg from all joints, in the total CCI/mLg, and in the mLg (p= 0,0001), during stance and swing. The variance partitioning revealed proportionally greater variation within-children than between children in the hip and ankle CCI/mLg, during stance, and in all joints during swing.
CONCLUSION: The results of this study demonstrated that the period of two months after gait acquisition was characterized by great variability in the use of neuromuscular mechanisms illustrated by the co-contraction indexes in the lower extremities. This variability was relatively greater between children, in the CCI/mLg of the knee and total indexes, in the stance phase of gait, compared to the variability observed in the same child through the longitudinal period. During the period of the study, the children presented different gravitational torques in the lower extremities and also, relatively greater variability in the individual use of neuromuscular mechanisms of the hip, in stance and swing phases of gait. These results suggest that the process of exploration and selection of motor patterns by typical children is characterized by great variability of individual strategies on neuromuscular mechanisms.