Postural adjustments during spontaneous and goal-directed arm movements inthe first half year of life

We studied the development of postural control during goal-directed reachin g and spontaneous arm movements in early infancy. Two groups of infants par ticipated. The first group consisted of 10 healthy infants, who were assess ed four times at the ages of 3, 4, 5 and 6 months. Each assessment consiste d of simultaneous recording of video-data and surface EMGs of arm, neck, tr unk, and leg muscles in various lying and sitting positions. Additionally, postural adjustments during spontaneous arm movements were studied in a sec ond group of five infants aged 1-3 months. Already before the onset of succ essful reaching, which occurred at 4-5 months, both spontaneous and goal-di rected arm movements were accompanied by a high amount of postural activity . During the goal-directed arm movements a preference for neck muscle activ ation and a direction specific organisation (dorsal postural muscles activa ted before the ventral antagonists) prevailed, whereas during spontaneous a rm movements such a specific postural organisation was absent. With increas ing age and concurrent with successful reaching, the amount of postural act ivity decreased. Still, the persisting postural activity continued to becom e more organised with increasing age. Position affected the postural adjust ments accompanying goal-directed arm movements at all ages. (C) 1999 Elsevi er Science B.V. All rights reserved.