Stance and gait perturbations in children: developmental aspects of compensatory mechanisms

The leg muscle EMG responses following perturbations during stance and gait were analysed in children between 1 and 8 years of age in order to study the development of those reflex systems responsible for the compensatory movements necessary to maintain body equilibrium. Single monosynaptic reflex potentials followed by a long-lasting (about 500 msec) polysynaptic gastrocnemius EMG response, along with coactivation of all antagonistic leg muscles, were characteristic of the EMG reactions following a treadmill acceleration impulse in early infancy. From 4 years of age on, the monosynaptic reflex potentials disappeared when perturbations were induced during gait. In addition, the polysynaptic reflex response became shorter (about 100 msec) and a reciprocal mode of leg muscle activation occurred, with a consequently more rapid and effective compensation of perturbation impulses. In older children with a disorder of the motor system acquired at an early age, a partial persistence of the immature motor responses could be observed, irrespective of whether the impairment was a cerebral lesion or a muscular dystrophy. It is concluded that the coactivation pattern is due to the immaturity of those nervous structures mediating afferent information necessary for the control of bipedal stance and gait. Furthermore, the existence of mutual inhibition of monosynaptic and polysynaptic spinal reflex responses, dependent on the function of supraspinal motor centres, can be assumed.