| Abstract: | When held upright, newborns show well-coordinated walking movements that normally cannot be elicited after about 2 mo of age. In contrast, spontaneous kicking in the supine position increases in frequency during the 1st 6 mo of age. In the present study, 8 2-wk-old infants were observed with a combination of a videotaped recording and concurrent EMG of 4 muscle groups of the legs. In a single session, Ss were viewed first kicking, then stepping. Kinematic, EMG, and motivational data indicate that kicking and stepping are the same muscle synergisms. The disappearance of stepping may be a result of the biodynamic consequences of the upright posture due to asynchronous development of muscle mass and concomitant strength. It is shown how this hypothesis explains training effects on prolonging the stepping reflex. (42 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) |
