My mantra: motor learning is specific to the task and context
Anyone following the TOMT 0-3 blog will know that I promote a task and context oriented approach to intervention because it is the only way to address the complex interactions between different aspects of task performance including visual pickup for motor planning, task dependent balance control, and learning through exploration, among other things.
I am busy working on an article covering the assessment and training of stepping up and down in toddlers. To this end I was doing a frame by frame analysis of stepping up onto steps of different heights and was thrilled to find a wonderful example of how a toddler adapts the motor plan to suit the context of the task.
Stepping up onto a low step
First we see Max stepping up onto a 5 cm step made of a high density compressed foam.
When stepping up onto a low step Max translates the COM forwards over the stance LE while at the same times flexing the hip and knee of the swing LE.
Notice that Max still lifts the foot higher than is necessary to clear the step.
Weight is then smoothly transferred forwards onto the left LE.
Once the weight is fully on the left, now stance LE, the COM is moved forwards by extending the left hip, in a smooth continuous movement.
Stepping up onto a 15 cm high step
However when faced with a 15 cm high step, the stepping-up action proceeds in a series of linked postural adjustments followed by LE movements.
Max first moves the left foot forwards, closer to the step and transfers weight laterally over the LE - the COM is translated to the left.
You also see how carefully Max visually monitors his actions.
The right hip and knee are flexed to lift the foot up, then the knee is extended to move the foot forwards over the step.
The COM remains centered over the right LE as he balances on the right LE.
Next Max plants the left foot on the step and shifts the weight forwards and laterally onto this new stance LE.
Notice how Max carefully balances on the stance limb as he moves the right foot up and forwards. This is associated with knee extension rather than hip extension.
Lastly he takes a small step forwards with the left foot - this small forwards step help the absorb the momentum created by moving the COM forwards.
Video clip: Max stepping up