There does not currently exist a well-defined method for characterizing prosthetic stiffness. Even the best prosthetic vendors simply base their stiffness recommendations on the reactions of a few ‘model users’ of various weights.

If we could combine a finely-tuned prosthetic stiffness with gait analysis, amputees could potentially function far better and with much less effort.

That was Biomechatronics grad student Emily Rogers’s guiding principle as she designed an adjustable-stiffness blade architecture, and my job was to develop a machine to describe the stiffness of blade prosthetics generally.

Drawing inspiration from the literature, particularly Shepherd (paper, paper), I designed an add-on to an Instron which would measure angular and horizontal displacements of the prosthetic tip. Combined with the vertical displacement measurement of the Instron, these can completely define the 2D stiffness of the prosthetic.