September 19, 2012
The Land of Oz
I’ve had quite a few questions in the past couple of months with regards to postural control. And it’s no wonder. Our collective experience reflects that this subject is not well covered in educational or professional development programs. And second, most of the research reads as if it comes from the Land of Oz – “Pay no attention to the lack of clinical relevance behind the curtain – the great Oz has spoken!” It’s confusing for many of us to interpret and not immediately applicable to clinical practice. So here’s hoping we can follow the yellow brick road and arrive at a clinically relevant understanding of balance – what is it, how it develops and how we can address it in our clients.
First let’s begin with the definition:
“Postural control involves controlling the body’s position in space for the purposes of stability and orientation and emerges from the interaction of multiple systems that are organized around a task.” (Shumway-Cook, Woollacott, 2007)
For the record, I am a huge fan of Shumway-Cook and Woollacott’s research. It’s both understandable and clinically useful – not an easy combination. The important part of this definition, I think, is the realization that postural control serves 2 purposes, stability and orientation to the task. As therapists we may naturally think of stability but considering orientation to a task as part of postural control may be a new piece of the puzzle for us. Both these components depend on processing sensory input from visual, proprioceptive and vestibular systems as well as the output of the motor system. As we will see, the road to mature postural control is a long journey.
Let’s follow along and look at the steps involved in the development of postural control……
Step #1: Postural control actually begins before birth. Many primitive movement patterns (=reflexes) are present in utero. These patterns provide the sensorimotor wiring required for postural control.
Step #2: The birth process itself prepares a tonal base that the baby can use against gravity. By virtue of pushing against resistance through the birth canal, the muscles on both sides of the body (the flexors and extensors) are activated.
Step #3: Physiological flexion in the newborn also allows the baby to maintain a level of organization and security in the face of that new entity called gravity.
Step #4: As the primitive movement patterns are triggered again, the muscles are now activated by the forces of gravity, creating the strength and coordination necessary to “hold and stay put” with a stable posture. Examples include the Moro, Tonic Labyrinthine, ATNR, STNR and Galant reflexes. The influence of most of these movement patterns is present between birth and 8 months.
Step #5: Soon physiological flexion and these primitive patterns are no longer enough to support the more complex tasks the baby is attempting. With the support of the tonal base and the wiring set up by the primitive movement patterns, righting, protective and equilibrium reactions begin to take their place. These reactions are still phasic and fairly stereotypical in nature, but they represent the brain’s quest to maintain head and trunk alignment in relation to gravity, and to keep the center of gravity within the base of support, thereby maintaining balance and a stable visual field. These reactions begin to be present in prone and supine at 1 – 2 months. They continue to develop in sitting and then in standing/walking until 2 years of age.
Step #6: The inner core muscle team gradually comes online during the first 2 – 3 years of life. The adult research tells us that this team works in the same way, every time we move, preparing a stable spine and pelvis before the actual movement. Optimal activity of the inner core is dependent on alignment of rib cage and pelvis. This alignment is crucial for the development of the postural reactions noted above and the postural adjustments to come. As the pediatric research progresses from measuring distal muscles to measuring trunk muscle activity in balance tasks, hopefully we’ll discover exactly where this preparatory pattern fits in the development of postural control.
Step #7: As development progresses again, we encounter the situation that the postural reactions are no longer enough to support the complex tasks the baby is attempting. So our brain develops further strategies to support movement: the anticipatory and reactive postural adjustments. These are multi-joint, variable postural adjustments that serve to efficiently control the center of gravity within the base of support in a manner that recruits and grades the motor response in relation to the anticipated/registered movement of the body. Ankle strategies and hip strategies are parts of anticipatory and reactive postural adjustments. The brain uses every level of processing of sensory and motor information to predict an appropriate response and adjust it throughout the task so that stability and orientation are achieved. These complex postural adjustments gradually develop and replace the postural reactions in different positions (sitting, standing, walking) between 6 months and 8 years of age. If conditions are complex (a sensory mismatch, for example), they are mastered even later at 12 years and into adolescence.
So there we have it, the yellow brick road of typical postural control. It may involve unexpected twists and turns as we develop new skills but just as in Oz, we end up where we’re supposed to be.
In our sequel, we’ll discuss children with movement challenges and where their postural control of veers off the road. We’ll also look at recent research regarding the development of balance in children with Cerebral Palsy and principles that we can incorporate directly into our treatment.