At the start of the chase, the cheetah propells its self by pushing down on its hind legs. The cheetah exponetially gains speed and only uses one side of its body at first, then uses the other side. Within the 2 first second the cheetah can accelerate to 45mph. This is when the hind leg muscles start to work in unison. The hind legs push down to thrust forward while the forelegs step alternately.