In this tutorial you have an opportunity to see how a toddler uses visual information to plan and adapt his actions to allow successful completion of a task. You also see how he adapts the alignment of the trunk and limb segments to maintain balance.
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