Comparison of forces developed by the leg of the rock lobster when walking free or on a treadmill

Summary In the free walking rock lobster the forces developed by legs 4 and 5 were investigated during the power stroke. Two orthogonal force components lying in the horizontal plane were measured. Based on these results the diffent tasks of the two legs during walking are discussed. The forces developed by leg 4 were compared when the animal walked freely and on a treadmill. In these two situations the results differ qualitatively as in driven walking the forces are nearly identical in a long series of consecutive steps whereas in free walking the forces can vary greatly from step to step. However, similar mean values of force were measured with those on the treadmill being somewhat higher. This shows that, although the treadmill is driven by a motor, the animal does perform active walking movements. In the treadmill situation the forces increase as the speed of treadmill motor is decreased.Supported by DAAD and DFG (Cr 58) for H. Cruse and by ATP (80 119.112) INSERM for F. Clarac