A leg's motion has four
phases, beginning with the foot on the ground. Then the foot lifts,
moves through the air, and returns to the ground again.
this motion into four phases, as follows:
at the leg keyframe where the leg's foot first touches the ground
and always corresponds with the start frame of a footstep in Track View
— Dope Sheet.
after touching, and before lifting. It is always in between the start
and end frames of a footstep in Track View — Dope Sheet.
at the keyframe where the leg's foot lifts off the ground, and always
corresponds to the end frame of each footstep in Track View — Dope
while the foot is in the air and is always in the intervals in between
steps in Track View — Dope Sheet. In walking, while one foot moves,
the body is supported by the other leg. In running or jumping, while
a foot moves there is a period where the body is not supported,
and moves in midair.