The study compares the relative validity of the data obtained from two experimental situations, i.e. free walking and driven walking, in relation to leg coordination in Jasus lalandii (Milne-Edwards).

The relationship between ipsilateral and contralateral legs during the forward as well as the backward walking sequences has been analysed in the two situations. They operate roughly in opposition. Although little difference in the mean phase values has been observed in the two experimental situations, the strength of coupling is greater in the driven walking animals.

The power stroke (PS) duration correlates well with the period, but the return stroke (RS) is more variable and varies according to the leg considered. The phase does not appear to be correlated with the step period during free walking, but is correlated in the treadmill situation.

Initially, several of the properties of the single motor unit discharges correlated with movement have identical mean values in both free and driven walking. However, several significant differences have been observed in the intra-burst organization. These differences indicate that the constraint of the treadmill decreases the variability of all parameters and produces a stable and more stereotyped walking pattern.

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