The stepping response in early infancy

Postnatally, the stepping response can be elicited right after birth, but s oon diminishes and disappears by about 2-3 months of age. It is still not c lear if the disappearance of the response is caused by gradual maturation o f the central nervous system, environmental factors, or biomechanical facto rs 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 infant s (n = 58) at the age of 6 weeks: 37 born preterm and corrected for gestati onal 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 studi ed by dividing the infants according to their birth weight status, and calc ulating the ponderal index (PI), leg volume (LV), and weight gain of each g roup. Preterm infants show more stepping responses, more muscle power discr epancies, and different leg volumes than their full-term counterparts. In a ddition, our results reported significant relationship between gestational age and relative birth weight on the manifestation of stepping response. Wi thin the preterm group the responses lingered longer in infants with shorte r gestational ages and in those with lower birth weight status. Consequentl y, 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.