Effects of body build and arousal on newborn infant stepping

Abstract

Newborn stepping is widely believed to be a "primitive reflex" whose disappearance signals cortical maturation. Observations of normal newborns showed that the number of steps was directly related to generalized behavioral arousal. In less highly distressed infants, those who were relatively heavier for their length stepped less. These results challenge the view that stepping is reflexively released by the upright posture and support the hypothesis that the movements disappear because infants' muscle strength may not be sufficient to lift their increasingly heavy legs.

Spontaneous kicking behavior in infants: Age-related effects of unilateral weighting

“…From the perspective of nonlinear dynamics, however, it has become clear that neural and behavioral changes do not map in a one-to-one way: Rates of change at the neural level might well be more gradual than those at the behavioral level (Farmer, 1990). Furthermore, the observed changes in spontaneous kicking might be influenced by changes in musculo -skeletal parameters such as absolute mass and centers of gravity of limbs and body segments (Thelen, Fisher, Ridley-Johnson, & Griffin, 1982; see also Thelen & Smith, 1994).…”

Upper and lower body functional asymmetries in the newborn: Do they have the same lateral biases?

“…While two studies reported a right-foot preference for stepping (Melekian, 1981;Peters & Petrie, 1979), two others found no lateral bias in this response (Kamptner, Cornwell, Fitzgerald, & Harris, 1985;Thelen, Fisher, Ridley-Johnson, & Griffin, 1982)-a finding that also was obtained for placing (Korczyn, Sage, & Karplus, 1978). Furthermore, three other studies tested both stepping and placing in the same newborns, and again, there was a lack of consistent findings.…”

“…As for expressions of ''footedness,'' two other considerations stem from the work of Thelen et al (1982). One concerns individual differences in body build or, in our case, the relative masses of the newborn's legs.…”

“…The other feature involves the latency time from elicitation to the first stepping or placing movement. Thelen et al (1982) did not examine whether latency time (or their anthropometric measures) had any bearing on asymmetries in leg movements during stepping; however, Grattan et al (1992) rated by means of direct observation the latencies for stepping and placing on a 5-point scale ranging from ''over 6-s delay'' to ''immediate.'' No asymmetries in latency time were noted.…”

Dynamical Analyses for Developmental Science: A Primer for Intrigued Scientists

“…For example, early work by Thelen and colleagues [Thelen, Fisher, & RidleyJohnson, 1984;Thelen, Fisher, Ridley-Johnson, & Griffin, 1982] focused on infant locomotion. They showed that the infant stepping reflex (order parameter) is a function of the infant's leg strength (control parameter).…”