Developmental course of general movements in early infancy. II. EMG correlates.
In order to study developmental changes in muscle co-ordination during the first postnatal months, simultaneous polymyographic recordings and video-recordings were made during spontaneous movements of 22 healthy infants, who were followed from birth onwards. During the first 2 months general movements (GM) change from movements with a so-called 'writhing' character, which have a tight appearance, a relatively slow speed and a limited amplitude, into GM with a 'fidgety' character, which consist of an ongoing flow of small, elegant movements. We hypothesized that this transformation would coincide with a change from a pattern of co-contraction of antagonistic muscle groups into a pattern of reciprocal activation. This was not the case, a pattern of co-activation of antagonistic muscle groups remained the prevailing pattern. With increasing age, we found shorter burst durations of phasic activity, an attenuation of burst amplitude and a decrease of tonic background activity. These changes were attributed to a reduction of the sensitivity of the motor units due to spinal and supraspinal reorganization. It is hypothesized that the so-called 'bistable' properties of motoneurones play a central role in the observed phenomena: in neonates motor units are apt at displaying sustained activity, at 2 months of age the threshold for reaching this maintained activity increases, resulting in a low level of excitation of motor units during spontaneous movements. In the third month rapid arm movements ('swipes' and 'swats') develop. The 'swats' are characterized by a consistent pattern of reciprocal activity of antagonistic (shoulder) muscles.
Hadders-Algra
M
M
Department of Developmental Neurology, University Hospital Groningen, The Netherlands.
Van Eykern
L A
LA
Klip-Van den Nieuwendijk
A W
AW
Prechtl
H F
HF
D004576:Electromyography; D004594:Electrophysiology; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D009068:Movement / Q000502:physiology*; D009132:Muscles / Q000502:physiology*