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