The ability to sit erect and reach to grasp toys on a raised surface is first seen when infants start to sit unsupported in a feeding chair with a tray.
Infants who have learned to sit independently are able to keep the head and trunk stable in the midline when using their hands for manipulation in the workspace directly in front of the body.
This alignment of vision, hands actions and objects (toy) allows the infant to link the information from vision, the position and movements of the hands and the shape and size of the objects and tools being manipulated. .
However, as soon as the child reaches up, or to one side with one hand, the trunk and UEs tend to move as a unit. So lifting of one hand above the head or the side may be associated with lateral flexion of the trunk.
When moving the hand to objects within easy reaching distance, young children are increasingly able to keep the head and trunk stable when moving the hand to objects within easy reaching distance.
Reaching further than arms length
Any action that requires reaching beyond arms length is produced by a combination of shoulder and elbow movements along with tipping and rotation of the trunk.
The exact combination of shoulder/elbow movements and trunk tipping and rotation depends on the direction of the hand movement .
Reaching forwards is associated with tipping the trunk forwards along with rotation of the trunk if the reach is with one hand.
Reaching to the side is associated with lateral weight transference over the pelvis and side flexion of the trunk in the contralateral direction.
Reaching across the body to the contralateral workspace is associated forwards rotation of the trunk.
Turning the head to look backwards and reaching backwards is associated with trunk rotation back on the ipsilatral side.
Bilateral manipulation of objects positioned on one side of the workspace
Sometimes a task involves using the hands to manipulate objects that are positioned in one side of the workspace.
When this is the case, the trunk is rotated so that the head and hands can retain their relationship to the midline of the trunk and keep the hands in th center of the visual field.
Reaching across beyond the body midline
Moving one hand past the midline of the trunk is not a common action. The movement requires the full range of adduction of the shoulder.
This is a movement used in special circumstance such as playing the piano.
In everyday tasks, reaching far across the middle of the workspace is usually accomplished by a combination of shoulder adduction and rotation of the trunk.
Sitting at a table influences the movements of the shoulder
Young children will often play sitting on the floor. Small range shoulder flexion movement to position the hands for grasping, manipulation and moving of objects that are within easy reaching distance.
Working at a table on the other hand requires increased range of movement at the shoulder in order to lift and position the hand for activities.
Young children adapt their reaching actions in a flexible manner
When young children are deeply engaged in an activity they use a variety of movement combinations to achieve their goals.
Here you see how Will (4y3m) coloring in a large picture using a series of fairly long strokes. He uses a flexion-extension movement of the elbow to draw the long strokes and changes direction of the stokes by either shifting his trunk or moving the paper.
Using flexion-extension movements of the elbow is a good solution to drawing long strokes. The alternative is to use a combination of shoulder and elbow movements to change the direction of the strokes - but at 4 years Will has not yet developed this complex level of coordination.
When he has finished the task he reaches far to the left with his right hand to put the marker away. The distance he is able to reach is due to the rotation of the trunk.