The Stepping Response in Early Infancy

Postnatally, the stepping response can be elicited right after birth, but soon diminishes and disappears by about 2 - 3 months of age. It is still not clear if the disappearance of the response is caused by gradual maturation of the central nervous system, environmental factors, or biomechanical factors such as added body weight and/or increased muscle mass of the legs. This clinical study assessed the stepping response in a group of healthy infants (n = 58) at the age of 6 weeks: 37 born preterm and corrected for gestational age. Quantitative measures of stepping response were obtained together with the qualitative measures of behavioural state and the distribution of active and passive muscle power of the legs. Mechanical factors were studied by dividing the infants according to their birth weight status, and calculating the ponderal index (PI), leg volume (LV), and weight gain of each group. Preterm infants show more stepping responses, more muscle power discrepancies, and different leg volumes than their full-term counterparts. In addition, our results reported significant relationship between gestational age and relative birth weight on the manifestation of stepping response. Within the preterm group the responses lingered longer in infants with shorter gestational ages and in those with lower birth weight status. Consequently, this study suggests that environmental experience and the time of birth of the infants play a more significant role than maturation and mechanical factors in the manifestation of the infantile stepping response.

Key words

Stepping response - Preterm and full-term infants - Maturation - Environmental experience - Muscle mass

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