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Updated: Aug 26, 2026
EEG Mu Rhythm in Typical and Atypical Development
Published on: April 9, 2014
Developmental course of general movements in early infancy. II. EMG correlates
M Hadders-Algra1, L A Van Eykern, A W Klip-Van den Nieuwendijk
1Department of Developmental Neurology, University Hospital Groningen, The Netherlands.
Insights
Muscle coordination in infants develops from writhing to fidgety general movements (GM). Despite expectations, co-activation, not reciprocal activation, dominated, with motor unit sensitivity changes influencing movement patterns.
Area of Science:
- Developmental neuroscience
- Motor control
- Infant motor development
Background:
- Early infant motor development involves significant changes in movement patterns.
- Understanding muscle coordination is crucial for assessing neurological development.
Purpose of the Study:
- To investigate developmental changes in muscle coordination during the first postnatal months.
- To analyze the transition of general movements (GM) from 'writhing' to 'fidgety' patterns.
- To examine the underlying muscle activation patterns during spontaneous infant movements.
Main Methods:
- Simultaneous polymyography and video recordings of 22 healthy infants from birth.
- Longitudinal observation of spontaneous movements during the first postnatal months.
- Analysis of muscle co-contraction and reciprocal activation patterns.
Main Results:
- General movements transitioned from 'writhing' to 'fidgety' character within the first two months.
- Co-activation of antagonistic muscle groups remained the predominant pattern, contrary to hypothesis.
- With age, shorter burst durations, reduced amplitude, and decreased tonic activity were observed.
- Development of rapid arm movements ('swipes' and 'swats') with reciprocal shoulder muscle activity by the third month.
Conclusions:
- Motor unit sensitivity changes, due to spinal and supraspinal reorganization, likely underlie observed developmental adjustments.
- Bistable properties of motoneurones are hypothesized to play a key role in neonatal and infant motor control.
- While co-activation persists, specific reciprocal patterns emerge for goal-directed movements like 'swats'.
Abstract:
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.
