{HEAD ~ A second leg ZMP position} representing {TAIL ~ a ZMP position} in the second single leg grounded period is then calculated 
representing
{ HEAD ~ A second leg ZMP position } representing { TAIL ~ a ZMP position } in the second single leg grounded period is then calculated
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH