Muscle Activity and Postural Behaviour in Newborn Infants – A Polymyographic Study

Abstract

In a group of 9 healthy newborns, spontaneous activity of different muscles was studied for 6 or 8 hours by means of surface electromyography on the 5th or 6th day of life. According to the local nursing routine the infants were placed in alternating left and right side positions. Averaged EMG activities were analysed with respect to behavioural states and observed postural behaviour. An improved recording technique and the logarithmic presentation of averaged EMG activities allowed the study of characteristics of tonic activity in state 1. The chin muscles showed the most specific EMG pattern in state 1. Chin muscle quiescence was observed during only 15% of that state. Lack of tonic activity was observed more in the beginning than at the end, but never in the middle of state 1. By visual analysis of 41 patterns of averaged EMG activities from the chin muscle it was found that increases of tonic activity only happen stepwise following concomitant phasic activities. Relaxation of tonic activity is either asymptotic or abrupt or by steps. The latter two are especially characteristic for the transition to state 2. Long periods of sustained tonic activity and low motility were characteristic for a long lasting state 1. The interval between the beginning of state 1 and the first increase of tonic activity varied more than the interval between the end of state 1 and the final drop of tonic activity back to the noise level. Other muscles showed less tonic activity in state 1: the neck area (sterncleidomastoid muscle 48% of state 1 time, trapezius m. 32%) was followed by the muscles of the forearm (extensor carpi m. 18%, flexor carpi m. 16%). These muscles also lead the rank order of the modulation of tonic activity. Tonic activity sustained for more than 30 sec. was not observed in state 2, except during transitions. In state 2 as in state 1 the muscles from chin, neck and upper extremities were more active than the muscles from the lower extremities. Durations of activities ranged from 28% (chin) to 13% (ant. tibialis) of state 2 time. No dominance of flexor muscles, which might account for the observed flexed posture, was found. Systematically changed side positions during the recording had no consistent effect on either motility or presence of tonic activity when corresponding muscles from the upper- and the lower-lying body side were compared during state 1. Likewise in state 2 no consistent effect on the total duration of phasic activity was observed. The results are discussed in relation to other known state dependent motor phenomena. It is suggested that sustained tonic activity results from an increased gain of the gamma-loop which may also contribute to the regularity of respiration. Differences between muscles probably reflect maturational and functional differences.

Learning about gravity: segmental assessment of upright control as infants develop independent sitting

“…The infants did not make many recognizable attempts to right themselves and gradually came to rest at the end of their available range. This stage is consistent with reports from previous researchers who found a period of limited postural responses to perturbation in 3-to 4-mo-old infants (Hedberg et al 2005;Woollacott et al 1987), lack of organized patterns of muscle activity to counteract gravity prior to 4 mo of age (Schloon et al 1976), and increased range and velocity of trunk collapse when trunk support was removed from infants while sitting erect (2-3 mo compared with 5 mo) (Harbourne 1993).…”

The Visual Scoring of Sleep in Infants 0 to 2 Months of Age

“…26,73 However, chin EMG activity may be inappropriately absent or low in 15-20% of the N sleep time in infants 40 w CA. 29 Similar percentages of absent chin EMG tone during N sleep are also seen 6-mo-old infants 26,74,75 and even in adults. 76 Two PSG markers best identify N sleep in infants 37-44 w CA: the discontinuous EEG pattern of TA and regularity of respiration.…”

Transcutaneous Oxygen Tension of Newborn Infants in Different Behavioral States

“…Changes in tonic activity are preceeded by a startle (25). The alternations in tone occur periodically and with a preferred time interval of 3 min (29). It would seem that the characteristic stepwise changes in tcPOz level and tonic activity are in some way related and possibly reflect alterations in muscle tone.…”

“…Polygraphic studies on newborn infants have shown that the tonic activity of muscle groups in the body during state 1 increases and decreases in a stepwise fashion (29). Changes in tonic activity are preceeded by a startle (25).…”