Mechanical muscle element

A mechanical muscle element, comprising an axially flexible convoluted circular tube having axially clustered pluralities of convolutions of first cross-sectional area between axially spaced convolutions of second cross-sectional area larger than said first area, first category rings in the spaces between first-area convolutions and radially inwardly confining the involved cluster of convolutions, second category rings in the spaces between each second-area convolution and the adjacent first-area convolution and radially inwardly confining the tube in each such space, first axially stiff interconnections between those second-category rings which enable said first interconnections to span at least two second-area convolutions and the cluster of first-area convolutions therebetween, and second axially stiff interconnections between those second-category rings which enable said second interconnections to span at least two second-area convolutions and the cluster of first-area convolutions therebetween, said first and second interconnections being in axial overlapping relation with opposite axial sides of the same second-area convolution, the effective sectional area of second-area convolutions being other than twice the effective sectional area of first-area convolutions, whereby changes in internal fluid pressure within said tube will induce related differential forces in a predetermined direction of change in the relative axial positioning of said first and second interconnections.