Balance control during gait initiation: State-of-the-art and research perspectives

Figure 6 Vertical braking of center of mass during gait initiation. This figure shows, from top to bottom, the timelines of the COM vertical acceleration (z’’), COM vertical velocity (z’), COM vertical position (z) as well as the electromyographical activity of stance leg triceps surae activity, i.e., soleus (Sol), gastrocnemius medialis (GM) and gastrocnemius lateralis (GL) of a single recording during gait initiation. The dashed lines indicate the instants of initiation (t0), foot off (FO) and foot contact (FC). As can be seen in the figure, step execution is accompanied by a downward (negative) COM acceleration. During mid-single stance, triceps surae activity counteracts gravity and brakes the vertical fall of COM. The braking action of COM is observable as a positive acceleration (top panel) which causes the vertical absolute velocity at foot contact to be lower than the peak absolute velocity measured in mid-single stance. COM: Center of mass.