I on both sides of the body at the same time, it is said to be moving in-phase, and the opposite phase difference would be 0. Successive phase difference is the relative time difference between moving legs on the same side of the body. If one step cycle takes 0.5 seconds, and leg II is 0.1 seconds behind leg III in its movement, the successive phase difference is 0.2. The three gait parameters are used to define a particular walking techinque. As well as the gait ratio, an arthropod's walking style is defined by its opposite and successive phase differences, or the time difference between moving legs on opposite and the same sides of the body.
Arthropods walking in phase move the same leg on each side of the body at the same time.
This has been interpreted as the animal changing from a swimming to a walking style of locomotion as it emerged from shallow water. As a consequence of this kind of interpretation, the appearance of out of phase trackways in the fossil record is taken as good evidence for the terrestrialisation of land by arthropods 4 .