Development of an Infant’s Peripheral Motor System Within the First 3 Years of Life as Studied Using Surface Electromyography

Relevance. Clinical assessment of condition of the neuromuscular system of a growing body is difficult in practice due to lability and instability of many neurological symptoms. Objective. Analysis of a child’s peripheral neuromuscular system development from the 33 gestational week to the end of 3 years (36 months) of postnatal life. Methods. The authors conducted a longitudinal sampling study observing the stratified randomization principles. The subjects were stratified by gestational and postnatal age, sex and neurological status. Results. The authors studied premature (31-32 gestational weeks) and term (38-39 gestational weeks) infants. Interference electromyograms (iEMG) of a premature infant within the first 6 weeks of life and a term infant within the first days of life were similar and characterized by “simplified” time structure, low amplitude and frequency. The dynamics of iEMG parameters in premature infants was low. Rapid increase in the non-linear iEMG parameters in term infants in the first year of life reflected on the complication of the iEMG signal. Linear iEMG parameters would monotonously increase in the course of the year. Maximum changes of the non-linear and linear analysis parameters were observed at the age of 6 month, which is a crucial period of development of corticospinal tracts and establishment of voluntary manipulative motions. Conclusion. The obtained data indicate importance of the first 2 weeks of life for the development of a term infant’s musculoskeletal system, within which a “mature” type of the motor neuron pool organization is formed. At the same time, quantitative changes observable in the iEMG (amplitude increase) continued throughout the 36 months of the study and indicate a continuing growth of skeletal muscles. iEMG of premature infants are peculiar in that they show a simpler time organization, which indicates a continuing “intrauterine” pattern of the motor neuron pool functioning.