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Are you wondering what crossing the midline is all about?
When Occupational Therapists and other professionals talk about “midline crossing”, the midline they are referring to is an imaginary line drawn from the head to the feet that separates the left and the right halves of the body.
Crossing this midline means that a body part (eg hand or foot) is able to spontaneously move over to the other side of the body to work there.
Click on the quick links below to find the information you need on this page:
Crossing of the body midline begins as early as infancy, when babies are learning to reach out for objects with both hands.
When an infant reaches with both hands to grasp a large object (eg a ball) that is positioned slightly to one side of the body, the child will end up crossing the midline to take hold of the object.
Bilateral movements and interaction with the environment are therefore important factors in helping a child develop the skill of crossing the midline.
Young children may tend to use the left hand on the left side of the body and the right hand on the right side of the body as they play. However, as body scheme, left-right discrimination and spatial perception continue to develop between the ages of 4 – 8 years, the ability to spontaneously cross the midline also continues to develop.
There is usually a lot of maturation in this skill between the ages of 6 and 8 years old, and the skill is usually fully integrated by the ages of 8-9 years.
As mentioned earlier, bilateral movements and interaction with the environment (such as caretakers playing with the child; the presence of objects to grasp) are important factors in helping a child develop the skill of crossing the midline.
Spending too much time in baby gear (car seats, bouncers), having too much screen time, or growing up in a deprived situation can affect how a baby interacts with the environment, and may limit opportunities for bimanual reaching and crossing the midline.
However, there is another vital factor in crossing the midline, and that is trunk rotation. If a child avoids rotating the trunk owing to poor core stability, and/or moves the trunk stiffly as a unit, then this may affect the child's ability to freely cross the midline.
You can see this in action in the photos below of a child throwing to a target off to her side:
The child has turned her lower body WITH the upper body, so the shoulders and the hips are moving as one unit as she throws.
There is no trunk rotation, which means she is not crossing her midline when she throws.
This is a better position: while sitting criss-cross, the child’s upper body has turned around (rotated), while her lower body (hips and legs) is stable and facing forward.
There is some trunk rotation and the child is crossing the midline with her throwing hand.
Many kids shift their body subtly to avoid rotating their trunks and therefore avoiding crossing their midline. It usually takes a trained eye to see when they are doing this, so please do take your child for an assessment if you are all concerned about a weak core and/or poor trunk rotation and/or avoiding midline crossing.
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Being able to cross the midline may help a baby or toddler to interact more fully with the environment. Even if the hand on one side is occupied, the infant can cross over with the other hand to grasp a new object.
This ability can help a toddler who needs to reach for an object while creeping/crawling, as well as babies who are learning to feed themselves.
Children need to develop a strong preferred hand for tool use (cutting with scissors, drawing with a crayon etc) by the time they start formal schooling.
The ability to spontaneously cross the midline plays an important role in developing a strong preferred hand, by enabling the preferred hand to practice on both sides of the body as it crosses over the midline.
If a child avoids crossing the midline, and uses the left hand on the left side of the body and the right hand on the right side of the body, then both hands will tend to get equal practice at developing fine motor skills, and the child’s true handedness may be apparently delayed. This may affect future handwriting skills.
Some children may struggle to easily cross the body midline. When a child shows hesitancy in reaching, stepping or looking across the midline of the body, this is known as midline crossing inhibition.
Sometimes this delay can be seen when a child hesitates or is clumsy during gross motor tasks which require the arm or leg to cross over to the other side.
Some children with delayed midline crossing skills may display some “compensatory mechanisms” in school that make writing really awkward for them. Have a look at the kids pictured below:
This girl has turned the paper sideways so she can write from bottom to top, instead of reaching over to her left side with her right hand to write from left to right.
This boy has shifted his body all the way over to the left, so his right hand does not have to reach over to work on his left side.
These girls have shifted their work over to the side to avoid crossing their midline while they work.
Kids who avoid crossing their midline just seem to take up more desk space as they shift their bodies, their chairs and their work to keep their writing hand on the same side of the body!
There are so many easy ways that you can help your child developing midline crossing skills:
These suggestions are completely free:
These suggestions are really affordable (the price of a couple of coffees) and soooo worth it if you are looking for LOTS of activities:
By popular request, I have made a Spanish handout of some of the information on my midline crossing pages.
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For those who like to dig deeper, this section below is for you!
The brain is divided into two sides, called the left and right hemispheres.
There is a mass of tissue between the two hemispheres, called the corpus callosum. The corpus callosum contains nerve fibers that allow the two hemispheres to communicate with each other in order to coordinate learning and movement.
A lack of midline crossing may indicate that the left and right sides of the brain (the left and right hemispheres) are not communicating well across the corpus callosum.
When a hand works in the space on the same side of the body (the ipsilateral space), only one brain hemisphere is used. When the hand or leg crosses over to complete a task on the opposite side of the body (the contralateral space), then both hemispheres of the brain are used. This requires more processing time owing to the communication/interaction between the hemispheres. These movements into contralateral space may also greater neurological organization than movements that don’t cross the midline.
Smits-Engelsman et al (2004) found that when doing activities that require midline crossing, younger children were found to make more errors and usually needed more time to complete the task than older children did.
It was suggested that the reason for the errors was the additional processing and neurological organization required to complete the tasks – the more mature brains were able to process and carry out the contralateral tasks more efficiently than the younger brains.
Cermak, S. and Ayres, J.A. (1984). Crossing the Body Midline in Learning-Disabled and Normal Children. The American Journal of Occupational Therapy. 38. 35-9. https://dx.doi.org/10.5014/ajot.38.1.35
Cermak, S.; Quintero, E.J. and Cohen, P.M. (1980). Developmental Age Trends in Crossing the Body Midline in Normal Children. The American Journal of Occupational Therapy. 34. 313-9. https://dx.doi.org/10.5014/ajot.34.5.313
Lombardi, J.A.; Surburg, P.; Eklund, S. and Koceja, D. (2000). Age Differences and Changes in Midline-Crossing Inhibition in the Lower Extremities. The Journals of Gerontology. Series A, Biological sciences and medical sciences. 55. M293-8. https://dx.doi.org/10.1093/gerona/55.5.M293
Provine, R. and Westerman, J.A. (1979). Crossing the Midline: Limits of Early Eye-Hand Behavior. Child Development. 50. 437-41. https://doi.org/10.1111/j.1467-8624.1979.tb04126.x
Smits-Engelsman, B.; Swinnen, S. and Duysens, Jacques. (2004). Are Graphomotor Tasks Affected By Working in the Contralateral Hemispace in 6- to 10-year-old Children?. Motor control. 8. 521-33. https://dx.doi.org/10.1123/mcj.8.4.521
van Hof, R.; van der Kamp, J. and Savelsbergh, G. (2002). The Relation of Unimanual and Bimanual Reaching to Crossing the Midline. Child Development. 73. 1353-62. https://dx.doi.org/10.1111/1467-8624.00476
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