MUD Mired in time...

For functional purposes we measure the trajectory (path) of the center of mass. Our favorite video analysis programs can select points directly [click] or use an average of two or more points by pulling a line out [click press- pull-release]. So, pulling a line across the body at the c of g level uses the line's center point. You can do the same thing with knees etc. We can easily get useful measurements from emailed home videos by grabbing stature from the video and (if actual height is known) typing in the known metric size of one stature. Here we are shown the 5 'wheels' that generate the single knee angle graph. The upper green one actually from the side would be seen more squished because it is actually leaning away from us and thus foreshortened as seen from the side. This is the center of mass to hip as radius of a wheel nearly the same size as the forefoot to ankle wheel. For this reason you cannot immobilize BOTH at the same time without adding jarring momentum epicycles to take their place. These smaller wheels adapt to the irregularities of ground surface and are driven by movement about their centers of inertia. An untethered talus allows inertial accommodation to ground driven foot postures as the talus moves within an envelope of tension and resistance created by the musculature forces that surround it.