December 9, 2014
Any rocket needs a great deal of force to push off the surface of the earth. And when I think about the spectrum of my clinical practice, all my kids with movement challenges have difficulty has difficulty accomplishing this same task. They are like a rocket without enough fuel – they have difficulty pushing off the surface in any position. We call this a generating a ground reaction force. And without this force, compensations will be required to keep from crashing back to earth. In sitting, I see my clients collapsed into a slumped posture, holding their head up with their hands, wrapping their feet around the legs of the desk, constantly changing position looking for a new stabilization strategy. Even if I ask them to place their feet on the ground, they can only manage it for a very short time. In standing they hyperextend their knees, collapse into hip and knee flexion, internally rotate at their hips and collapse at the medial arches of their feet. I’m sure you can identify more biomechanical compensations you see when your clients are trying to stay upright against gravity.
But what might be the difficulty with the generation of a ground reaction force? Well as usual, there may be more than one system involved.
The vestibular component: The powerful vestibular system serves to stabilize our gaze but it also a large impact on our postural control, by virtue of its input to the postural tone of the anti-gravity extensors of the trunk, it’s impact on the development of anti-gravity flexion and its involvement in our postural adjustments. Dysfunction in registration or processing of vestibular input can manifest in decreased vestibular input to anti-gravity muscle tone, central stability and/or postural adjustments (1).
The proprioceptive component: This system allows us to make sense of our own body, its position and our movement in space (2). When it is working well we sense the resistance from the floor in our joints and muscles and we “push back” against it. And yes, it’s intimately connected with the vestibular system (3).
The musculoskeletal component: Our muscles clearly create output for pushing against the surface. Alignment affects how available the muscles are for activation. Keep in mind however, that they are an output and outputs are organized only after sensory input gives us enough information so our brain can figure out what should happen.
The central stability component: The pressure that is generated in our trunk in coordination with the inner core muscles contributes to the stability of our spine and pelvis and has a great deal to do with staying upright against gravity and stable in midline (4). It also positively influences the output of distal muscles (5). (You can observe this in children with low tone. As their central stability improves, there is a definite decrease in knee hyperextension and collapse of the arches of the feet.)
The next time you see a child who seems to be struggling to push off the surface, take time to assess each of these components and see where the child might benefit from input. That input could be crucial to their ability to develop ground control.
Here is a favourite preparatory treatment activity of mine. It combines alignment and activation of the inner core team using breathing with heavy resistance at both the upper and lower extremities. Lots of layers incorporated here.
This post was written for PediStaff, a great resource for therapists. You can find them at www.pediastaff.com.
1. Christy JB, Payne J, Azuero A, Formby C. Reliability and diagnostic accuracy of clinical tests of vestibular function for children. Ped Phys Ther. 2014; 26:180-190.
2. Yack E, Sutton S, Aquilla P. Building Bridges Through Sensory Integration. Future Horizons Inc. Arlington, Texas. 2002.
3. Barthel K. Evidence and Art. Merging Forces in Pediatric Therapy. Labyrinth Journeys. Victoria, BC. 2004.
4. Evidence Based Core Stability For Children With Challenges: Part 1 and 2. Mannell S, Wiebe JW. Section on Pediatrics Education Session, APTA Combined Sections Meeting, San Diego, CA. Feb 2013.
5. Hodges PW, Gandevia SC. Changes in intra-abdominal pressure during postural and respiratory actions of the diaphragm. J of App Physiol. 2000; 89(3); 967-76.