Shift happens………..



Therapists often talk about weight shift – where it happens and why it happens in the way that it does.  One of the hallmarks of typical development is a child’s ability to begin to initiate weight shift from the pelvis in sitting at 10-12 months of age.  Prior to this initiation of weight shift occurred through upper trunk movement.  The significance of this change is not lost on us: if the upper trunk is initiating weight shift, then the arms are not free to participate in other functions during the movement.  I see this most clearly when children with movement challenges shift their weight by flexing their trunk sideways during walking rather than shifting their weight at the pelvis.  But how does this “shift” in the shift come about?

As usual, it has to do with central stability.  We need to have a stable spine and pelvis in order to create a mature weight shift.  Our four inner core muscles, the anticipatory core as we call it (for more information visit previous posts, here and here) create a developing central stability over the first years of life through their contributions to IAP (= intra-abdominal pressure).  You will note that the first responders of the anticipatory core team are the respiratory diaphragm and the pelvic floor muscles.  That’s right people, activation of the pelvic floor is an important component in development of babies’ postural control – who knew?

However, these anticipatory core muscles can’t go it alone, they need help from other muscles in the trunk: the reactive core.  Almost as soon as movement begins, 2 sets of reactive core muscles start to work together.  Tummy time begins to activate the Posterior Oblique Synergist and the Anterior Oblique Synergist ** (for more information visit here).  As babies breathe deeper, rotate their body over their hips and begin to crawl on hands and knees, these activities promote the participation of the pelvic floor, which improves that crucial stability of the pelvis from the inside out.  In addition, 2 more sets of reactive core synergists, the Lateral and Rotational Synergists**, ramp up their activity around the hip and stabilize the femur.  Activation of the diaphragm and pelvic floor for central stability and subsequent recruitment of the synergists set the child up to be able to initiate weight shift from the pelvis rather than the upper trunk.

When our clients display lateral flexion for weight shift rather than initiation from the pelvis, this demonstrates the continued use of an earlier developmental pattern to compensate for inadequate anticipatory and reactive core activation and inside-out recruitment pattern.  This use of lateral flexion prevents the development of mature balance and the independence of the upper extremities from the trunk.



Watch babies as they learn to crawl.  Do you see their bottom “waving” back and forth? This is a clue that they are not stabilizing their pelvis during movement.

Observe your clients carefully as they crawl or walk.  Do they laterally flex to shift their weight instead of weight shifting at their pelvis and rotating their trunk?  If they are laterally flexing, they lack adequate stability of the pelvis for weight shift.


Posterior Oblique Synergist (POS) = contralateral gluteus maximus and  latissimus dorsi   (Dianne Lee)   Anterior Oblique Synergist (AOS) = contralateral abdominal obliques and hip adductors   (Dianne Lee) Lateral Synergist =  Gluteus medius/minimus and contralateral hip adductors   (Dianne Lee)   Rotational Synergist = Gluteus maximus, deep hip rotators (obturator internus), ipsilateral hip adductors and psoas  (Julie Wiebe)


Additional reading:

Bizzi E, Cheung VCK. The neural origin of muscle synergies.  Frontiers in computational neuroscience.  2013; 7: article 51.


This blog was written for PediaStaff, a great resource for therapists.  You can find them at 


5 thoughts on “Shift happens………..

  1. Thank you very much for available information to indicate treatment for children with cerebral palsy. Especially we can know that spastic diplegia chilren have instability trunk and show us lateral weight shifting throug walkikng or crawling. But I think we really consider that Is children’s waving of bottome clue of poor core stability? We have to check a fixed pattern of upper trunk. Some physical therapis may say that mobility can make a stability. I agree their opinion. What do you think of this opinion? I’m sorry my english was poor.

    • Hello and thanks for your note, you did wonderfully in english! I totally agree that for some children there may be limited upper trunk mobility when they are in 4 point but most often I see a non-reciprocal pattern of crawling (i.e. bunny hopping) with these children rather than the side flexion pattern I noted in the blog. Stability and mobility go together in my mind; we actually don’t develop quality stability without mobility nor can we have quality mobility without stability. Thanks for your insight.

  2. Hello,
    How would you work on pelvis stability specifically as compared to trunk stability, in babies, and in older children? Thank you very much for your blog, it is very helpful.

    • Hi Melanie, that’s a great question! Pelvic stability was always a piece that challenged me before I understood the anticipatory core and how to treat it. With babies, alignment and timing when handling are the key. The pelvis should be slightly forward of 90° and the rib cage should be “stacked” over top of that pelvis, with the ribs in a horizontal alignment; this allows for better activation of the diaphragm. Since pelvic stability develops from the inside out, the pelvic floor muscles need to be active in order to develop good pelvic stability. Your handling of movement facilitates weight shift initiation from the pelvis, rather than the upper trunk, and is timed such that the child is moving on an exhale, allowing improved activation of pelvic floor muscles in response to diaphragm loading on the inhale.
      With older children who are more involved the approach is the same as young ones. With older children who are more cognitively aware you can train umbrella breathing (= improved excursion of diaphragm), teach them to control their alignment and then always move with an exhale (not breath holding). When we restore the anticipatory to reactive core recruitment, we improve pelvic stability.
      Hope that provides some assistance with your question. The approach to training the anticipatory core and reactive muscle synergists is our Dynamic Core for Kids course. We’re teaching online Oct 3-4, 2015 and may have an on-demand course available after that.