MUD Mired in time...

Nature does not like THAT! Also, the bigger the angular arc of the circle used, the more upward and then following downward the travel. More up and down engages gravity? Noooooooooooooooo. That is not efficient. Skateboard UP a hill? Better have extreme inertia. What is best, theoretically? A========================>B A dead straight horizontal line at uniform speed. Without wheels, this is nearly impossible and actually impractical. Wheels without roads are not so good. Wheels are a one trick pony. Jointed limbs have contour options. Legs win. But the laboratory is flat and so this huge distinction gets little mention. The yellow arrows might be a wheel solution. But sine waves are what legs can do. A big sine wave (green line) uses much more energy than a low amplitude sine wave (red).

The biologic target is a nearly flat low amplitude sine wave travel of our center of mass.

Legs are designed to do exactly that. They can allow, on the fly, alterations to offset ground irregularities. The coordinated tricks to attain the flattest uniform travel are called the ‘determinants of gait’. This was a great advance in thinking, but keep in mind that, as good as this was for amputees, it had no allowance for neurologic abnormality. The 6 movement tricks (‘determinants’) allow compensation for missing parts or rigid ankles when replaced by prosthetics. [Psst...You can’t say ‘tricks’ in medicine!!!]