PMC

Following movement initiation, the COP translates posterior and lateral towards the initial swing limb (S1 or APA phase). As the heel of the initial swing limb leaves the ground, the COP translates laterally towards the initial stance limb (S2 or Transitional phase). Finally, as the initial stance limb leaves the ground to complete the initial step, the COP translates anteriorly (S3 or Locomotor phase).

The COP point at each instant is transformed to the local xyz coordinate system (see ), where the mean of these points are used to define the heel point H. The progression of the COP points as a function of time is indicated by the arrow. A point Q is defined in order to perform a parameter sensitivity analysis. This point lies 1 cm away from H in lateral (x), posterior (−y) and inferior (−z) direction. The gray areas are drawn to roughly indicate the boundaries of the undeformed heel.

Anterior-posterior (AP) displacement of the center of pressure (CoP) and vertical displacement of the leading heel in a representative subject. Thin traces represent single trials, which are time aligned to the heel-off (vertical green line). Red thick trace in the upper plot represents the average CoP displacement. Notably, the high trial-by-trial variability of CoP makes the automatic identification of the CoP onset difficult and error-prone in each single trial. The vertical red line marks the CoP shift onset as identified on the average CoP trace.

The agreement between net vertical force and COP recorded by the insole and forceplate during the preferred walking trial (a) and running trial (b) for one subject. Good agreement in the COP is seen between the insole and forceplate data from 10 to 80% of the gait cycle. However, the insole COP tends to be anterior to the forceplate COP during heel contact and then posterior to the forceplate COP approaching toe-off (the last 20% of stance).